The Physiology of Transport Substances in the Blood (Sodium)


By Professor Marcel Uluitu, M.D. Ph.D.

Spiru Haret University

Bucharest, Romania


Co-Authored by Diana Popa (Uluitu), M.D.

Department of Microbiology, Immunology and Molecular Genetics

University of Kentucky, Lexington, Kentucky, USA


[Editor’s Note: This paper is presented as Part III of a series of chapters from the new book “The Physiology of Transport Substances in the Blood (Sodium)”; subsequent chapters will be featured in upcoming issues of this Journal. This segment features Section III (of three sections) of Chapter Two, Chapter Three and Chapter 4 (of six chapters)]



Chapter 2 (Section III):


The Blood-Vascular Space



2.8. Na transport in the blood.

Na chemical activity in the blood is conditioned by its interaction with local components.
It is carried mostly in a bound state. In the method presented one describes the interaction of heparin anionic sites with Na and serotonin (5HT) cations. The interaction occurs with different energy, according to the equations (217, 218)

         Na + heparin (H) = H-Na with an energy of interaction = E

          5HT + H = H-5HT interaction with energy E
     Initially, E Eand in the mixture there are 
          5HT+ Na + H  = H-Na + 5HT. If Na is involved in interactions with other substances, E will decrease until  EE, and the equation will become
          5HT + Na + H  = H-5HT + Na . In this case Na chemical activity is lower.
  So the serum Na chemical activity refers to the interaction of 5HT with H  which is the reference for estimating the activity of Na.

The determinations show that the chemical activity of Na is lower than the reference value. This is consistent with normal nervous excitability. The increase of the Na chemical activity is accompanied by increased neuromuscular excitability: in rats by audiogenic seizures, hypermotility, etc.In humans, they are expressed by behavior disorders of constitutional type, EEG abnormalities, attention deficit disorders, disorders of hemodynamic (see chapters of physiopathology). The interaction of Na with proteins in the blood represents a barrier of energy in the way of Na motion as a result of decrease of its chemical activity (218).

Na – proteins interaction in the blood has a regulatory role for cation transport and also for mass transfer to endocellular space of the excitable structure (218).
The chemical nature of the bonds discussed above, between Na with proteins and the intensity of interaction are dependent on the variation of molecular parameters of substances and of solvent. Na ligandation depends first on the anionic and cationic composition of the solution (183) (Table 11), not only on the concentration of ligand.
The ligandation depends also on extraprotein factors (solvent, Na) on molecular protein factors(density and nature of anionic and cationic sites (Tb.11), conformation, hydration, etc. Water, structured by hydrogen bond, is fixed on the lateral, polarizable radicals and on the covalent bond (208, 160),it stabilizes the protein molecule. Breking of the hydrogen bonds of water induces protein denaturation and loss of Na (218).


Unpolarizable Na induces protein conformational changes, increases the strength of anionic sites field (208, 166) and interacts with the water dipole. The intensity of these influences is reduced in the presence of other anions in solution and depends on the strength of the cationic field  of hydrated Na.The loss of water molecules shortens ionic radius (Tab.9) (173, 126) and thus increases the energy of interaction. The energy of interaction is thus variable, it falls asymptotic to "0" from the center of ions towards periphery, defining in this manner a number of crystalline rays (120) of the ions.The charge of Na ions induces the increase of the energy of anionic sites of proteins and  diminishing rays of interaction of the cation field. It interacts with all kinds of anions in blood (tb.11). The degree of interaction depends on the polarizability anions. The Na interaction with protein sites anion has decreased as a result of its chemical activity and its capacity to react with other anions. Proteins are the most important substances for the transport of Na. Proteins are amfoteric substances,  have great plasticity and thereby enable the accommodation of various other ligands (191). Their capacity of transport depends on their nativity (Table 17). Interacting with metals they  modify their charge by  transferring  electrons from the metal. The intensity of interaction of  anionic sites  of proteins with cations depends on other factors as well , such as  (10) the number of coordination, the amino acid composition, polarizability of anino groups (Ling cit.16).

Strength sites is also influenced by internal neighboring groups, with variable polarity interacting through inductive forces, with intensity dependent on the square of the distance between them (120). The activity of proteins depends on the degree of dissociation of anionic sites, according to the theory of multiple equilibrium (112): it increases with the length of the polypeptide chain, with the pH of the solution and the intensity of the electrostatic forces (4, 20, 191). The affinity of proteins decreases by denaturation (233), the interest of coordination involving prototropic groups of the aminoacids residue aspartame, glutamic, histidine, treonine, cysteine, arginine. The charge density of the proteins , decisively  influences the interaction with CATIONS. Its decrease diminishes the  afinity for cations(166). The density of the charge of anionic sites  induces the formation of a cationic cloud around them causing an unequal distribution of cations in the neighborhood (161). The selection for monovalent cations (20) depends on the charge density of the anionic electrostatic field and their degree of hydration (20,181,170). The amount of the charge density of the proteins influences inversely proportional the activity in solution of sodium (165.62).


The main issue is to decipher the mechanisms of Na transport in the blood. The data presented so far do not suggest an individualized transporter but present a general process in which  blood proteins  , or a multitude of anionic groups with which Na can interact , are involved. The type of binding, as well  , is not identified, being represented by interactions that have been discussed at length. These are weak interactions that have an influence mainly by their number and type , rather than by their strength. Therefore the equilibrium of the three compartments does not  depend only upon the gradient of the cation but also on the  distribution of anionic groups between compartments. On the other hand the existence of olygoenergetic bonds ( weaker  than between 5HT and heparin, taken as a reference value in the method used by us in this research ) enables us to underline some physicochemical properties of Na-proteins interaction. Sodium involved in various complex interactions, is in equilibrium with its free form, chemically active, as demonstrated by the method of competition and it is compatible with the functional manifestations of the excitable tissues. Increased chemical activity in humans and rats is accompanied by cerebral hyperexcitability .There are no data available to explain, among other things, the transfer mechanism of Na to the level of  the excitable membranes, or the blocking of ionic channels by using toxins.


Na interacts with any kind of anions from the blood ( table 11 )




        2.9. Method of determining the Na activity in blood serum. (Method of competition 5HT / Na for anionic sites of heparin)



        2.9.1. Principle of method.



For dynamic dialysis  the competition is determined between  Na cations and serotonin (5HT) for the anionic sites of polyanion heparin (H).

Their affinity for heparin is different and can be described by equations:

       Eq. 1: Na (mM)+ H(mg) Na-H     with interaction energy = E 

       Eq. 2: 5HT (g)+H(mg ) HT-H   with interaction energy = E 

       Since EE we have:

       Eq 3: 5HT + Na + H  Na-H + 5HT  Eq.3 is valid for any solution that contains the active chemical Na, and interacts with other substances with    EE. In the presence of blood serum, the above equations are written as follows:
       Eq.4: Native serum (sn) + H + 5HT  5HT-H + sn.

       Eq.5: sn + Na + H + 5HT Na -H + 5HT + sn. Na is of exogenous origin.

       Eq.6: denatured serum (sd)+ 5HT + H Na-H + 5HT. Na has endogenous blood origin. Dialysis allows to obtain the necessary values to calculate and to identify the heparin anionic sites.



     2.9.2. Equipment.
Spectrofluorometer sensitive to ultraviolet, with double monochromator for the separation of excitation radiation (= 295 m) of fluorescence radiation (= 340 m) for establishing the serotonin.
 Dialysis cell. (Figure 4).

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The dialysis cell is made of a balloon with round bottom (1), with a polished  neck in which a glass tube is mounted(4), polished as well  (3), with the outer end open , where reactants are being introduced into the cellophane bag(2). This may be replaced by a rubber stopper pierced by a glass tube.  The neck of the balloon has an orifice (5) where the solution of 0.25 M sucrose is inserted in which the cellophane bag is immersed. The system is equipped with a device for  fixation on the agitator (6).



 Preparation of the equipment.


A prerequisite is to avoid contact with  ions of other  source or ion exchangers, detergents. For this purpose glassware is abundantly flushed with double distilled water, dried  and siliconed . Ion exchangers  will not be used because fine particles of them can remain in water and modify the reactivity of proteins and the interaction with Na. The same steps  are required in the preparation of cellophane bags. Solutions are to be prepared only with distilled water.



        2.9.3. Reagents: heparin, serotonin, sucrose, NaCl, water.
(1) heparin powder, G.M. = 10,000 - 20,000. It has anionic groups as SO H, active at pH close to neutrality.
(2), serotonin (5-hydroxi-tryptamine = 5HT) as a serotonin-creatine-sulfate solution of 1g active substance in one  milliliter of sucrose solution of 0.25 M
(3) Sucrose p.a. 0.25 M as a medium of isotonic reaction.
(4) NaCl p.a.
(5) bi-distilled water.


           2.9.4. Technical procedure.

Calculations are carried out with the dialysis cell thermostatically controlled and stirred  with a speed  of 80 cycles / min. The characteristics of  the 5HT dialysis in the bag is determined both in the absence and in the  presence of different concentrations of heparin (Figure 5, Table 14). The rate of the liquid volumes : there are 2 ml reactants in the solution of 0.25 M sucrose in the bag and outside the bag there are 58 ml 0.25 M sucrose solution in which the 5HT from the bag dialyzes , thus expressing the processes that take place before dialyzation.   


   Characterization of the dialysis bags

The permeability of bags against heparin is to be checked. A spectrophotometric measurement is to be made in the dialysis fluid outside the bag, in order to see the color resulting from heparin with toluidine blue. Should heparin pass through the pores of the cellophane bag, alteration of results can be avoided  by acetylating the bags by dipping them into a mixture of acetic anhydride and pyridine until the reaction with blue toluidine becomes negative, or else other bags can be tested.



   Measurement of the dialysis coefficient

0.1704 M (60 g) serotonin active substance in 2 ml final volume of sucrose solution 0.25 M are to be introduced in the cellophane bag. At the end of the dialysis, outside the bag there will be a concentration of 5HT of 1 g /ml, the increase of which is measured every  5 min. (tables 14, 15). Passing of  5HT outside the bag takes place under the law of diffusion of Fick (103) described as :

          Eq. 7    (C - C) / (C- C = e       where :

C - C = concentration rate at 5HT EVRY "t" = 5 min.
C - C = concentration 5HT rate at "t" = "0"
"D" = coefficient of diffusion.
"T" = time in minutes.
  = constant characteristics that include bag: thickness, porosity, etc.
  = 1 / v x 1 / v

One  bag can be used several times after washing with  bidistiled water  for 10 -15 minutes, using the same "D". Comparative measurements allow the  and to be automatically included  into the  "D" value .

The calculation of diffusion coefficient "D" depending on the concentration of heparin (Table 15, Fig 5) and under the influence of Na (Table 16 and Figure 6).

          Eq. 8  (C-C) / (C - C) =e of Ficks law leads to the conclusion that  the process


of diffusion depends only on the nature and  physical-chemical status of the diffusible substance, 5HT (18). "D" is used to calculate 5HT-free running , diffusible in the mixture of reactances in the bag.

   Figure 5.  Dynamics of the 5HT dialys in the  bag , in the presence of variable quantities of heparin and in the absence of it (232)





 Figure 6. Dynamics of the 5HT dialysis in the bag , in the presence of 0,5 mg of heparin and of variable quantities of  Na and in the  absence of it(232).



2.9.5. Determination Na/5HT competition for anionic sites of heparin. Determination of anionic sites of heparin.

  Table 14. Diffusion coefficient (D) depending on the concentration of heparin (232)

heparin     0     1.25     0.25     0.375       0,5        0 75
  "D"    0 0624  0,0725   0,065    0,0593    0,06085      0,0561

   Table 15. Diffusion coefficient (D) in the presence of variable amounts of Na (232).
Na mEq/ml         0       4,5      9       18      32
    D          0.0609   0,0608   0,063   0,0608  0,0614


    Table 16. M anionic sites depending on the concentration of heparin(232)

heparin mg/ml    0.175     0.25    0.375     0.5     0.75     1,o 

M anionic      0,0136   0, 02  0 041 0,0603 0,0747 0,0899
   sites         0,004      0,0021   0,002  0.00505  0 012    0,009


1 mg heparin, 60 g serotonin, complex salt in 0.25 M sucrose, the final amount of 2.0 ml , are being introduced into the dialysis bag. The bag is immersed  in the 58 ml dialysis solution, sucrose 0.25 M. The  dialysis cell thus prepared is fixed on the stirring device (Fig 4) and  introduced into the bath with a temperature of 200,1 C and stirred with a frequency of 80 cycle / min. At baseline in the bag there are two forms of serotonin: one free, dialyzable and other bonded, in interaction with the anionic sites of heparin. While 5HT free running is difusing outside the bag , the  equilibrium between the bonded and the free forms left in the bag is disturbed ,  initiating thus  defixation processes  (Fig. 6) which  maintains the concentration rate  of the free form. The reaction continues until  an equilibrium is reached between the interaction energy  5HT-heparin and the strength of dialysis induced by  the concentration rate (Fig 6). To determine the parameters of interaction ligand - heparin (number of anionic sites of heparin and the association constant  ligand - heparin) the free and bonded  serotonin quantity is determined during dialysis, at intervals of 5 minutes, until the equilibrium dialysis is reached . The calculation of the two forms of 5HT is by Eq.9.

       Eq.9: dC/dt = - DC that:

C = total concentration of the ligand (free + bound) of the bag every "t" = 5 min.
C = concentration of the free ligand every t = 5 min.
D  = coefficient of diffusion of 5HT.


     This equation is not satisfactory because the time interval of 5 minutes  is very short and gives large errors especially when the absolute diffusion and the variation of concentrations outside the bag are small (120) close to the equilibrium of dialysis, when processes of defixation are small as compared to those of diffusion of ligand. Therefore the form of successive approximation of eq. 9 is recommended.

       Eq. 10: C = (v + v) /vx C/1 –e     in which


C = concentration of the free ligand  from the bag at "t" = 0 corresponding to each point of determination.
C = 5HT concentration of dialysate every "t" = 5 min
v = volume of liquid in the bag
v = volume of liquid outside the bag
D  = coefficient of diffusion.
   The value of C (the amount of serotonin fixed at t = 0)results from the value of C.
C = amount of free 5HT every "t" with the equations:

      Eq. 11:  C = C - C

       Eq. 12:   C = C - C

C : is the initial amount of serotonine. Eq 10 allows highlighting decomplexation processes that characterize multiple equilibriums  of the polyanion with small ions by the graphical representation of the equation 13:


       Eq.13 v + v / vx C = f(1-e) (Fig 7)

Non linear graph indicates the presence of defixation processes.

Figure 7. The dependence of the number of anionic sites with high affinity for serotonin (μM) upon the concentration of heparin (mg) (232)

  The calculation of the association constant 5HT / heparin and of the number of anionic sites


The equation of multiple equilibriums is used for this purpose . (Eq 14).

     Eq.14 :  C= (nK-Ce / 1+KC + e) which for a small number of sites can be written as  Scatchard’s Eg (181),(Eq. 15)

     Eq.15 :  C/C = nK -KC       where 

n = number (M) anionic sites
K = constant association of complex heparin-5HT.


   Information is thus obtained about the influence of small cations that compete for 5HT anionic sites of heparin, when they are free in solution and about the interaction energy equal  or bigger than E2 (Fig. 7). (Tb.16) shows the number of anionic sites at different concentrations of heparin and the existence of defixation processes.



 Determination of the 5HT – Na competition.


Heparin (0.5 mg / ml) 5 HT (30 g / ml) and variable amounts of NaCl in sucrose 0.25 M are introduced into the dislysis bag. Further the above mentioned  protocol is to be observed. Fig. (6, 7 and GT 17) show the displacement of 5HT by Na+ in the heparin complex , the curves getting closer to those obtained for determination of diffusion coefficient (Fig.5). In Figure 11 the semi logarithmic strait line represents  a constant of exchange. The dependence of competitiveness processes  Na+ / 5HT depending on the amount of active chemical Na+ can be noticed.

       Figure 8. 5HT loss from the dialysis bag under various influences (- ○ - the  reactant couple alone; x the reactant couple in the presence of native serum; - ● - native serum with no other addition; - 5HT single reactant in the bag) (232)



  The influence of native blood serum on the 5HT/heparin complex.



Collecting blood serum has to be made under the conditions necessary to preserve the native state of macromolecular components of the plasma. The blood is collected in tubes prepared as above. The blood is collected through free flowing to avoid foaming. To store 15-20 minutes at room temperature. Avoid low temperatures between 0 and 8C because they induce severe changes to serum reactivity macromolecules. It is centrifuged for 10 minutes at 2000 rpm. Blood serum is separated in an other tube by free flowing, and the clot is discarded. The content of protein, total electrolytes (by flam photometry) and chemical activity of serum cations , of which 95% is Na+ , are determined in the serum.

To determine the chemical activity of Na+ , 0.15 ml serum, heparin and serotonin in the quantities mentioned above are to be introduced into the cellophane bag. The data obtained from  the dialysis of the  serotonin in the bag are represented graphically (fig.9)

         Table 17. Scatchard’ Eg. parameters as: n =M sites / ml solution and the PK of the sites in each group (232)


reactants present        n      n     n     pK      pK       pK

0.5 mg heparin (H)       -       -      0 06    -        -        6,06
0, 15 ml native serum(SN)  0,256  0 07    0,0393 4,047    4,89      6,113
0, 15 ml (sn)+(H)        0,246  0103    0,0664 4,285    5,033     6,15
0, 15 ml (sn)+(H)+ 
Eq Na              0,205  0,066    -     4,129    5,35       -
0, 15 ml (sn)+(H)+
Eq Na              -       -       -      -        -         -
0, 15ml ser denatur.    
-       -       -      -        -         -


       Figure 9. - The influence of denaturizing upon the reaction 5HT-protein, as compared with native blood serum ( native serum ● 0.15 ml; ○  denatured serum 0.15 ml, "x" 0.15 ml native serum, and Na 37 μEq) (232)





     The influence of denatured blood serum upon the interaction 5HT/heparine.


The denaturizing of the serum is made by vigorously shaking the tube , thus avoiding the addition of other chemicals.  0.15 ml of this serum is used instead of native serum. Further , the above steps will be followed. The results of dialysis 5HT (Fig.9) show that serotonin values are similar to those obtained when the ligand is the only reagent in the bag, not interacting  with heparin.


         Figure 10. Representation of the number of sets of sites with high affinity for serotonin. Every set is identified by pK under the  image of each set in various combinations, including native and denaturized blood serum (232).



   influence of exogenous Na on 5HT/heparină interaction in the presence of native serum.
Variable amounts of NaCl solution are added into the bag containing native serum . The curve of 5HT dialysis outside the bag is similar to that obtained only with serotonin and to that where only denatured blood serum has been used. (Fig.8, 9).
 Determination and identification of the number of anionic sites of heparin in the presence of blood serum.


This is done by graphical representation of Eq. (15) by Scatchard (Fig 11, Tab 17).In the presence of denatured serum , heparin does  not interact with 5HT and a straight line, parallel to the abscise ,is obtained(Fig.12). The subtraction point by point of the two curves (Fig.12) can also be used.

Figure 11.The graphic calculation of the number of anionic sites in the native and denatured  blood serum (232).


         Figure12.Direct and semi logarithmic representation of decrease in the number of anionic sites with affinity for 5Ht under the influence of variable quantities of Na (232)

        Figure 13.Quantitative binding of 5 HT ( Scatchard’s meth.) upon anionic sites in a mixture of serum and heparin (○ couple reactant heparin + 5HT; ● couple reactant + native serum 0.15 ml ; CF = mM bound serotonin / l solution; CL = mM free serotonin / l solution) (232)


       Figure 14. Graph equation CF = f(CL), where CF = 5HT bonded  on sites anionics; CL = free 5HT  (1) = native serum  containing 10 mg% protein + serotonin (2) = native serum containing 10 mg% proteins +  0.5 mg heparin+  5HT (3) = native serum with 10 mg% proteins + 0.5mg heparin + serotonin + 0.15 M NaCl (4) = difference point by point between curve 2 and curve 1 representing μM serotonin fixed on the anionic sites in the environment. (232).



      In conclusion, the method allows the determination of plasma Na+ activity and its interaction with proteins , as related to the reference value of the interaction of 5HT with the heparin polyanion.




Chapter 3:

  Extra Cellular Matrix (ECM)

          3.1. General.

The cells of any tissue are held together by occlusive junctions, which anchor the cytoskeleton on  the fundamental substance , the extra cellular matrix. The distribution of the fundamental substance is uneven. In some tissues it is hard to identify , like in epithelial tissues, poorly represented in the brain and spinal cord and in very large quantities in bone and connective tissue (33, 66, 73, 111). The matrix is composed of a variety of proteins and polysaccharides  locally secreted and assembled into a network in close contact with the surface of the producing cells. With all this variety of distribution and structure, there is communication between all its departments and they, remarkably maintain the essential aspects of the tissue of origin (92, 171). Quantitative and structural variations of the  matrix satisfy the requirements of the function of each tissue ( calcified forms in bones, transparent ones in the cornea, etc.). The pericellular matrix , rich in carbohydrates , is organized as a network.


The matrix and the cytoskeleton are intimately associated (116). Macromolecules from the matrix, in their turn , orientate the cytoskeleton. In the area of separation between an epithelium and the connective tissue (5),the matrix structures intself  as a thin and hard baseline membrane , which plays an important role in controlling the cellular compartment, in the development , proliferation, shape and function  of the cell (55).



         3.2. The role of ECM.

First of all , it  physically stabilizes the parenchyma tissue, which it is part of .It has multiple biochemical , informational , physical-chemical , metabolical etc. influences. It maintains a constant character of cellular environment and protects the parenchyma from variations in the blood  composition , temporarily stores substances until they are eliminated or included into the cell function. It mediates and modulates exchanges of substance between the vascular and endocelular spaces : electrolytes, fatty acids, oxygen, carbon dioxide, etc. It modulates the activity of (140) of the compounds from cell environment, optimizing the intake of substances in the cell. It has structures which analyze the composition of intercellular matrix and of the  endocellular medium. It participates in the direct intercellular communication. The matrix releases soluble factors under cell influences, with response from the cells themselves. There are complex relations of interdependence between the parenchyma cells and ECM : mechanical, biochemical, information embryo genetic, immunological, transportation, etc. Between the cells and the components of ECM there are connections of adherence and molecular interaction.


3.3. The chemical composition of ECM. (156).

ECM macromolecules belong to two classes of substances: (1) glycozaminoglycans (gag), which are made of free polysaccharide chains and (2) Proteoglycans, composed of five groups: glycoproteins, collagen, elastin, fibronectine and integrins.
(1) Glycozaminoglycans (mucopolyzaharid) consist of unbranched chains of repeated units of aminosugers: -acetylglucozamin, acetylgalactozamin mostly sulfated and associated with other types of sugar, uronic acids (iduronate and glicuroni). The sulphate, carboxylic and hydroxyl groups in their composition confer upon them an important electronegative charge with an important functional role. They occupy large spaces and are very hydrophilic; they define hydrated and porous gels in which the cells are enclavated. Their negative charges attract clouds of osmotically active Na+ and large quantities of water. The matrix (140) has great inflation pressure. The porous gels allow the diffusion of hydro soluble molecules according to their size and electrical charge, such as hormones, ions, catabolites, etc. There are four groups of special gags by the composition of sugars, type of connection between them, place and number of sulfate groups: hialuronan, condroitin, dermatan sulfate, heparan sulfate cheratan sulfate, heparin. Hialuronan, hialuronic acid locally synthesized conditions tissue swelling especially in saline medium (62).


Collagen and hialuronan are structural, abundant components of the connective tissue. These are counterbalanced by the network of collagen(162). Hialuronan surrounds the neuron leaving a  perineuronal space. Glycosaminoglycan controls bivalent ions (238). So does  heparansulfat (209, 210). Glucuronic acid combined with condroitinsulfate is also a good absorber of shocks. Condroitinsulfate is very rich in negative groups and works as an ions exchanger. (2) Proteoglicans (glycosylate glycoprotein) are constituted of multi sulphurated gags (68), as covalently connected chains on which many gag chains are fixed like proteins on a  protein core , usually a glycoprotein (156). They are extremely heterogeneous. They have negative electrical charge given by fragments of sulfated sugars (162). Glycoproteins from the proteoglicans structure are components of matrix, in interaction with cells. When they have hialuronan in their structure, they induce the cell membrane. For many types of cells they act as real receptors (116). They are able to transmit  biochemical, hormonal, metabolic, etc signals which influence the intracellular processes. They are connected to the  cytoskeleton. They are the so-called "mosaic proteins” , spread in the body, some very specialized when they are included in the constitution of the base membrane. Due to the ability of gelatin extra cell pericellular matrix,  cavities  of various sizes and with different charges are formed  serving to select the cells and molecules. They play a role in chemical intercell signaling.


They regulate the activity of other proteins such as protease inhibitors and proteolytic inhibitors by immobilizing  protease in the production place, limiting the sphere of action by steric blocking  or by creating reserves of proteins, by protection  against proteolize. They may increase or decrease the concentration of proteins by presentation of receptors on the surface of the cell. They may be associated with the fibrous matrix proteins (collagen or protein from the network of basal lamina). They interact with other proteins in ECM as elastin, collagen, fibronectin, laminin, etc.. As polyanions , they are in interaction with cations and cationic groups. It is hydrophilic and permits the turgescence of tissues.They are components of plasmatic  membranes. They participate in cell adhesion and intercellular relationships. The fibronectin binds the cell with the matrix (5). At the ends there are carboxylic groups. It is also present in blood plasma, where it participates in the process of blood clotting.

From the electronomicroscopic point of view there have been shown physical connections - head to head between filaments of fibronectin in the ECM and the intracell  actin filaments . The molecule has three fields on the α chains: cellular, membrane and extracellular having aspartic acid residues of which compete in the binding of bivalent intracellular cations.  Collagen is the  major protein of ECM, secreted by the cells of connective tissue.


They are fibrous proteins, twisted in the triple helix rich in proline and glycine. The triple helix (25) originates in the hydrogen bondings between OH groups of hydroxylizin and hydroxyprolin. In the brain ECM there  is the type IV collagen . The type IV molecule  forms a network included in the composition of lamina base.

    ECM relationship with neurons.


The characteristics of matrix molecules suggest that they control the function of tissues in which they are located. In the excitable tissues, proteins have intensely negative charge and interact with cations.


The ECM interactions are mediated by some matrix receptors (molecules on the cell surface which bind themselves to the matrix components). In fact it is not possible to specify the place where the membrane component ends and where the membrane matrix starts. The last binding between them is made through a transmembrane protein which binds the matrix to the citoskeleton. The most important receptors on the cell membrane are very specialized integrins (laminine, entactine, tensine, etc...), which are binding to the matrix proteins (collagen) (116).


The integrins binding is weak but their value is given by their number. Integrins are composed of two subunits and bind themselves to transmembrane protein matrix. Their intracellular domains are NH2- terminals, while the matrix ends are COOH-terminals.The extracellular domain matrix interacts with bivalent cations. On a cell there are several types of integrines. Their function is very diverse. In order to have the cell to bind to the  matrix, integrines interact with the cytoskeleton through protein intracell, actine and fibronectine (162).



        3.4. Cerebral matrix.

         3.4.1. General

The organization and the chemical composition show features that ensure optimal environment for the neuron. It is composed of the capillary space, the cellular neuron and the glia and by the extracellular matrix with varying sizes (73). The neurons of the central nervous system are multipolar, excitable cells. They respond to chemical stimuli, transmiting excitation to other neurons and to the effectors. At the level of the synapses, the stimulus is transmitted by means of chemical mediators. Stimuli are encoded and stored as memory or used by conjugation with other stimuli in mental processes, etc.. Neurons are constituted of the  pericarion and of extensions (dendrites and axon). The neurons in the brain are associated in nuclei. Association neurons are entirely situated  (including the processes) in the brain tissue.


         3.4.2. Nevroglia.
Derives, like neurons, from the ectoderm (182). There are six types of  glial cells.
(1) Schwann cells, forming the myelin sheath around nerve receptors.
(2) oligodendroglia form the myelin sheath around the axon of nerve centres.
(3) microglia consists of phagocytes, migratory cells in the brain. It removes cell debris.
(4) the astrocyte  regulates the transition of molecules from blood to the brain.
(5) ependymal cells coat the cerebral ventricle and channel ependima.
(6) satellite cells, which support neurons in the peripheral nervous system. The astrocyte is a glial cell, great, stellated with many branching extensions which end as "feet" (187). They represent from 50% in the cerebral cortex to 90% in many other areas of the total brain volume (73). It is a polarized cell (128), the extension  being in contact with a cell of mesodermic origin (microvascular endothelial cell) which it covers (187) and by another extension it is in contact with the structures of ectodermic origin –neuronal synapse,  which it covers . They are ideally positioned to maintain synaptic activity and energy metabolism of the local environment of the neuron (126). The astrocyte mediates interaction vessel - neuron,  which stabilises them.It has strucural and molecular characteristics (115). The cytoskeleton of the astrocytes has three types of proteins (143, 177): Actin microfilaments of 6 nm in diameter, microtubule of 29 nm diameter microfilaments and intermediate (IF = Intermediate filaments) with a diameter between 8 -12 nm. Glial IF proteins are fibrillar, acidic (glial fibrillary acidic proteins = GFAP). GFAP is the most specific marker for astrocytes in both normal and pathological conditions. The role of GFAP is given by the large number of anionic groups which is stabilizing the cytoskeleton, astrocytes maintain shape through interaction between glial filaments with nuclear and plasma membranes. The ratio of neurons and  noneuronic cells vary by species,depending on the brain area, on age (128). An astrocyte / neuron ration = 10 / 1 is specific for most regions of the brain (128). Astrocytes come into contact with the surface ablumen of the capillary endothelial cells and their terminal feet capillaries cover the capillary almost entirely (187). The astrocyte functions are multiple and condition the neuron activity. The astrocyte is interposed between capillary and neuron and thereby plays an unspecific role of filter between the capillary and the neuron (Fig.15).


The exchange between these two areas is done through various mechanisms: diffusion, active transport, electrostatic interaction,  endocitosis, exocytosis, selective transport imposed by that barrier. Astrocytes play key roles in the energy distribution of substances in the blood, (128) mediate glucose intake as a first barrier to nerve cells. Perisynaptic processes incorporate glutamate during synaptic activity in  somato-sensorial areas. Glutamate is incorporated by astrocites through a mechanism dependent on Na in the proportion of three cations for a molecule of glutamate / 128).


Na in the extracellular medium achieves an electrochemical gradient, so that glutamate is recycled within the glia. The astrocyte participating in the synapse function  and reincorporation of the neurotransmitter, vesicle fusion ,as well as its local catabolization. The astrocyte also has  a secretory activity. The products secreted by astrocytes together with the secretion of the endothelial cells are constituents of the blood-brain barrier. The secretion of the astrocyte maintains the  characteristic of the blood-brain barrier and of intercell junction . In culture, the astrocyte secretes laminine, fibronectine, chondroitinsulphate, collagen.  The collagen stimulates endothelial cells maturation. They in turn stimulate the growth of astrocytes. So, with the mixed secretion of the two cell types the functionality of the blood-brain barrier is ensured.  The network formed by the " vascular astrocyte processes" also plays a mechanic role by absorbtion of vascular pulsations, which are no longer transmitted to the neuron.


       Figure nr.15. The diagram represents the astrocyte role in angiogenesis and functional hyperaemia. Glutamate release (1) of neuronal presynaptic that binds to receptors on astrocyte, activating phospholipase and diglycerol lipase (2) to release  arahidonic acid from astrocytes (3). The conversion of arahidonic acid to epoxygenase under the influence of cytochrome C450 2C11 (4). This increases output K + ,which prevents hyperpolarisation (5) and vascular dilatation. At the same time it increases Ca2 + intracellularly and stimulates both mitogenesis and angiogenesis. (187)


3.4.3. Cerebrospinal fluid (CSF) (174).
The brain contains 80% water, of which 20% is extracellular water, blood and CSF, main component of the extracellular fluid. It is secreted by the plexus ventricular choroid, whose walls are directly permeable for plasma components. The active transport of plasma solvates has a barrier of the epithelial cells of the choroid plexus, which regulates the osmotic balance produced by the passage of water through the existing gradient. Choroid plexuses secrete about 2 / 3 of CSF,the  rest being produced by endothelial capillary (174). The rate of secretion is of 0, 35 ml / min., i.e. 500 ml / day. CSF flows from the lateral ventricles,through Monroe's foramen, into ventricle III, and through the Sylvian aqueduct into ventricle IV. Through Magendie's foramens it passes into the subarahnoidian space, between the three meninges membranes. Then it passes into the spinal canal. In the subarachnoid space, it irrigates the cerebral cortex . Solvates with small sizes diffuse freely in the extracellular fluid and CSF through the perivascular spaces, cross the ependymal system to the ventricle and from there, through a valve system,it goes into the venous blood of the subarahnoidian space.


                        Table 18

Chemical composition ,by comparison to blood - CSF (78).

                                         CSF                  blood


      Water % 99 93                      99                    93
      protein mg / ml                    35                  7000   
      glucose                            60                    90
      Na mEq %o                         138                   138
      K  mEq %o                           2.8                  4.5
      Ca                                  2.1                  4.8
      pH                                  7,33                 7,41
      osmolarity                       2950                 2950


3.4.4. Lymphatic system

The lymphatic system is one of the ways of communication between the three areas: Intravascular,interstitial and endocelular. Lymphatic capillaries begin in the interstitial space, and through lymphatic vessels carry to the interstitial fluid vessels the result of capillary filtration, secreted and  enriched with compounds produced at cellular level and metabolytes.It is absent at brain level.




Chapter 4:


Exchanges Between Capillaries and Interstices


        4.1. Capillary.
        The capillary function is regulated by chemical and physical factors. The first act in intercellular signaling ways,by specific transcription factors, proteins, etc.. The  capillary wall consists generally of an endothelial cell layer as a central element programmer (164), situated on the baseline membrane (174). Endothelial cells form a selective permeability barrier, secrete some specific compounds involved in metabolic local processes and regulate contractility of smooth muscle fibers (32). The luminal surface of the endothelium is covered with proteoglicans, glycoproteins and glycocalyx composed of fibers. This layer has a thickness of 20 nm and is rich in negative electric charges (102) with variable density. This layer is covered in turn by a layer of absorbed plasma proteins forming a 1m thick net, rich in carboxylic groups, sulfate, sugars (acid N-acetyl neuraminic, mannosil, galactosil, N-acetylglucosamine, sialil residue) protein glycoconjugat represented by integrine selectine, immunoglobulins. To endothelial cells are associated proteoglican heparansulphate , glycosoaminoglicans. The chemical composition and physical properties are influenced by local differential adsorption of plasma proteins: albumin, fibrinogen, orosomucoid. Serum albumin stabilizes endothelium-blood interface, influences the function of barrier against macromolecules occupying anionic sites on glycocalyx and endothelium.The perfusion with   solution without albumin increases the permeability of capillaries in muscle and mesenter. Orosomucoide reduces permeability to macromolecules anionic capillaries in the muscles of rats. Glycocalyx is a dynamic structure as a barrier to macromolecules. Its structure and its reactivity vary depending on different vascular territories of change. The structure of glycocalyx includes the sialic acid and acid glycoproteins (162). It controls the exchanges cell-capillaries, increases the permeability for small hydrophilic solvates(33). Therefore the structure and chemical composition of the wall of the capillary tissue irrigated is important for the transport in the extravascular space.



           4.1.1. Endothelial capillary.
Endothelial cells united by strong junctions constitute a barrier in the transport blood - neuron for many compounds including ions (137). Endothelial cells in the brain are different from those of other territories (21, 22),have electrical resistance 1.000 ohm between them, while on other territories the resistance is only 10 ohm / cm (174), are impermeable to macromolecules (50, 249 ), have different mechanisms of transport (22). At this level, the crossing is by specific processes of endocytosis, mediated by the receptors which bind the ligand in the beginning and transfer it by internalization in vesicules to the opposite side, where it is released by exocytosis, and the transfer to neurons is selected by the blood-brain barrier. The system controls extravasation cerebral capillary blood components and expansion of extracellular matrix liquid. There participates in this process also the polyanionic component of extracellular matrix to maintain the cationic composition of the neuronal environment (73, 25, 157) and blood component that controls the activity of Na (231, 233, 236). This protects the neuron against large variations of the Na gradient. There is therefore a complex control of transepitelial transport of substance (77). Cell adhesion proteins of brain capillaries grow by ischemisation which promotes activity in the focal leucocytes (79). Endothelial cells do not communicate between them.Their matrix surface is covered by astrocytes with their processes. Another surface of membrane adheres to the baseline. Through another surface  they are in large contact with the blood and its components. This luminal cell surface is covered, regardless of the vascular territory, by layers of mobile plasma 1 m thick (see above). It covers a layer of macromolecules made up of  by proteoglicans, glycoproteins and by glycocalyx, to which plasma proteins areattached. On this surface there are to be found Integrines, which provide cell adhesion to the transmembrane receivers and binds extracellular cell protein. Major vascular Integrines interact with specific vitronectine and fibronectine, which fixes the cells of extracellular matrix. Laminine binds the membrane epithelium to the baseline membrane. The nature of Glycocalyx and the number of anionic sites of the endothelial cells in the brain differ from that of other vascular beds. A protein of  astrocyte origin induces the synthesis of proteoglicans in the cell endothelia and increases the selectivity df blood brain barrier. Due to the negative charge of glycocalyx (98) and endothelium, anionic molecules  penetrate the brain with more difficulty  than neutral or cationic molecules of equal sizes. On the baseline membrane anionic sites are less abundant and are part of a mixture of proteoglicans, hydrophilic amino acids, glycopeptides, sialic acid residues, heparansulphate. In the same area there are other molecules bound by the membrane: selectine, Integrine, immunoglobulins, glycolipids, glycoproteins, and proteoglicans, with role in the inflammatory processes and coagulation. From the reactive composition of this segment mention should be made of the richness in negative charges of the carboxylic groups, sulphates, hydroxilic, N- acetil glucosaminic and of monosacharides: manosil, galactose, fucose. Proteoglicans with long branched  chain are associated to endothelial cells in a  50 - 90%ration . Plasma proteins (albumin, fibrinogen, orosomucoid) adsorbed by the capillary wall, change the properties of chemical and physical-chemical molecular layer of endothelial cells .The cationisation of serum albumin, immunoglobulin and antibodies considerably increases the passage of substances in the brain (Triguero, 1989 , Partridge, 1991). There are no data however to support any  role of plasma proteins in the blood-brain barrier. The arrier is affected by injection in the brain of  hypertone solutions in experimental cerebral hypertension in infections, etc. This process occurs through redistribution or the loss of anionic sites on the cerebral endothelium. The layer of extracellular substances, bound to the endothelial cell membrane, covers the intercellular spaces as a network of plasma proteins adsorbed on the strongly acid membrane, which binds cations. During the ripening process there takes place the remodeling on both sides of the endothelium, the development and maturation of baseline membranes can be a mechanism of differentiation of the brain microvascular system.



              4.2. The blood-brain barrier (BBB).
BBB is made up of endothelial cells which limit the intraluminal portion of the brain capillaries, a layer composed of the feet juxtaposition of astrocyte processes and baseline subepithelial membrane(50, 74). Endothelial cells present (41, 98) specialized regions by the help of which they form close contacts (intercellular junction), have high electrical resistance, have no fenestration, and minor pinocytose activity. In the BBB structure there are also described both the luminal and abluminal plasma membranes (74).

The endothelium has the role of endothelial barrier to substances in the blood, the selective membrane for substances in both spaces ,through  transcellular mechanisms.The basement lamina itself forms a barrier between capillary and neuron, is located between astrocyte and endothelium, acting as a filter . Thickness : 40 -120 nm. By means of electronic microscopy it is possible to see that it is made up of 2 distinct layers: (5): lamina lucida (lamina rara) adjacent to the plasma portion of the endothelial cells and of lamina densa, an electrono – dense layer. A third layer is further described, lamina fibroreticulata, binding the basement lamina to connective tissue. Basement lamina is a filtrable structure, polarizes the cell, influences the endothelial cell metabolism, organizes proteins on the adjacent plasma membrane etc.  It plays a role in synaptic reconstruction, guided nerve regeneration in time, etc. In the constitution of BBB there is found collagen type IV, heparansulphate laminine, fibronectin. Between neurons and astrocyte, the barrier is richer in proteoglicans. Collagen type IV is flexible and forms networks, stabilized by disulphuric bridges . The  membrane also contains agricans secreted by neurons surrounding the  synapsis. Maintaining the  brain function requires a certain extracellular ionic strength, especially metabolic conditions, neurotransmitters, growth factors, etc. between certain limits of variation maintained by the BBB. It accumulates (174) catabolites, ions (specialy K) for their removal, into the membrane endothelia there is found a large amount of Na,K-ATPaze. In the astrocyte endings  there is a  high density of channels K (73). At the level of synapsis there are accumulated , during the nervous  pathways activity (sensory, and of multiple neural circuits ), neurotransmitters which are inactivated by removal  or local metabolisation. From among these, (128) for example , glutamate that is inactivated by reuptake in astrocytes perisynapsis with the help of transporters and glial electrochemical gradients of Na (172).The thus enabled transportation represents a key signal for coupling neuronal activity with activation of glycolysis in the astrocyte. The transport of solvates from the  blood into the brain is done either by specific transporters, or in a transendothelial way , by plexus choroides. BBB provides the necessary amino acids in the extraneuronal environment and protects neurons by large fluctuations in the content of Na (174).The change of BBB permeability allows brain penetration of the same substances that are not transporters, (5) such as lipophilic molecules, hydrophobic , according to the partition coefficient and they reach the brain extra cellular space. The barrier allows the passage of substances also due to the concentration gradient. The size of molecules and their steric configuration together with the above mentioned factors conditions the BBB function.



       4.2.1. Adjusting the BBB function.

For the proper functioning of the brain, the energy and plastic substances requirement makes BBB to respond to cellular signals and to monitor the transport of substances and ions (74, 28, 99). From the studies on transport processes it results that strongly polarized substances like glucose, some amino acids, etc. are crossing with difficulty the  lipid membrane of BBB and are transported by  transcellular saturable systems, on the endothelial cell membranes. The Na+-dependent transport of amino acids is made by abluminal membrane, and neutral amino acid transport, by gradient of concentration. In contrast, the transport of neutral aminoacids , independent of Na+ is made by both membranes. It is difficult to quantify transport routes , as their number is very large (87) and they overlap. BBB is penetrated by cations and cationized antibodies. The function is dependent of Na.K.ATP and of the saturable transport system operating in parallel. It is a complex system of incorporation of Na23,  when the concentration of Na+ or H+ in the cell increases . It is inhibited by cations Na+, H+, Li+, NH+ extracellular.



4.2.2. Cerebral territories without BBB.

Circulating hormones influence the central nervous system with access to neurons in certain areas where the barrier is permeable because of the endothelial fenestration (187): the posterior hyophysis , medial eminence and the pineal gland which releases neurohormons from nervous endings. In capillaries without fenestrations there are many vesicles in cellular cytoplasm carrying in a transcellular way various substances. In the hypophysis , the absence of the barrier allows the passing of neurosecretion into the  blood. In the subfornix body there is a chemoreceptor area. The transcellular transport at this level enables balancing of water and of other homeostatic functions. The regions without BBB are isolated from the rest of the brain by specialized ependymal cells called tenocytest , localized along the surface III ventricle , near the median line. This is the sensory-circumventricular body which includes the vascular organ, lamina terminalis, subfornix organ, organ subcomisural area postrema, eminence median, neurohypophysis and plexus choroid. The tonicytes are associated by tight junctions and prevent the free exchange between circumventricular body and CSF. Badly bounded area and defined topographically , it also contains some heterogeneous structures which limit the internal walls of the cerebral ventricle. Terminalis lamina ending  on the median wall rostral ventricle III contains two circumventricular sensors , which control the hydrosalin balance. Ventral of organum vasculosum laminae terminalis is the recesus supraoptic where the osmoreceptor center is located . The target place  of angiotensin II is the subfornix organum  placed dorsally  and caudally from the above comisura, enabled by ADH.  Therefore it has a neuroendocrine function and has  highly variable receptors for steroids, angiotensin II, atrial natriuretic hormone  and somatostatin.



            4.3. Kidney territory.

        4.3.1. Renal functional unit.

The structural and functional support of the kidney is the nephron: vasculo-tubular structure. The vascular part is between the renal artery and vein including a mirabilis system : the afferent arteriol capillarises  first as vascular glomerule Malpighi. The efferent arteriol capilarises from here a  second time in the peritubular area. It continues as vasa recta to venula kidney. Nephron begin by Bowman's capsule, invagination of the tube surrounding vascular glomerulus. It continues through the proximal convoluted portion, loop of Henle, with a  distal convoluted portion having a segment descending and ascending the following constituted of a large portion and other thinner, filiform . It continues through the straight collecting tubules, with the opening to the renal pyramid . The adjoining vasculo-tubular structures are separated by an interstice of unequal size. The tubes  are made of a membrane baseline on which there are placed , in the proximal convoluted portion contort , irregular cuboidal cells, rich in cytoplasm, having  protoplasmic extensions  on the inner face - brush border. These cells present invaginations with mitochondria. In the Henle loop , the   cells are extremely thin, flattened, with clear cytoplasm. In the contort distal tubes , the epithelial cells are cuboidal , smaller , having clear cytoplasm and smooth surface.


      The structure of renal vessels. The glomerular capillaries are in large contact with the space encapsulation. In the cytoplasm of endothelial cells there are perforations of 0.1 on the internal face and perforations of 100 in the baseline membrane, through which the plasma passes into the capillary lumen, through filtration. The efferent glomerular vessels are relatively permeable and also for the molecules of albumin size. The blood circulation in the area of the thin loop of Henle is upwards, in counter current with the uriniferous tube. This vessel has a fenestrated epithelium up to the return of the vasa recta. The interstice between capillary and tubes consists of some wider and some narrow areas. At the level of the proximal contort tube , the space is represented by the merger of the membranes of the tubes and capillaries. Endothelial capillaries present fenestrations of 0.05, through which the tubular content passes directly into the blood vessels. Here  there take  place resorption processes for approx. 74% of the glomerular filtrate. Otherwise the space is wide. The size of the interstice is increasing toward the deep kidney regions. Interstice contains many mucopolisacharides rich in proteins and anionic sites with high basicity , which can be modified through changes in loading with water, Na+, or under hormonal influences. In rats with diabetes insipidus , the basicity of proteins is increased in the medulla. ADH increases the number of anionic charges, arresting more and more  Na+ , with or without water.  The interstice also contains some serum proteins , brought here by  vascular fenestration, mostly  albumins . These , together with the basic proteins , are important in Na+ reabsorption.



4.3.2. The mechanism of urine formation.

The fundamental theory was proposed by Cushing in 1917 and includes three processes: (1) glomerular filtration of plasma, (2) selective tubular resorption, (3) tubular secretion. Formation of urine is the result of a dynamic process of communication between  the three spaces: vascular, interstitial and tubular (222, 137). Ureogenesis function is done with the participation of hemodynamic factors (blood pressure, blood output, stroke volume, etc..) membrane factors (permeability, structure, chemical composition); intratubular speed of the ultrafiltered and the primary urine, components of the glomerular ultrafiltered.



Metabolic factors: general metabolism, acido-basic status, blood composition, energy dependent transport, simple diffusion (144), gradients of concentration, electrochemical gradients, molecular interactions. Physical and chemical factors like colloid-osmotic pressure, viscosity, protein content, electric charges and molecular polyelectrolyte, cations. Harmonization of activities of these factors and their adapting to conditions of the body is regulated nervous and humoral (221, 230) in the context of the theory of multifactorial urogenesis.

The endocrine factors have an important regulating role . Aldosterone acts at the level of the distal contort tube and of collector tubes. The inactivation of local protein synthesis and of Na.K.ATP is involved in the Na+ retention. DOCA acts in  the same way as aldosterone, but weaker. The atrial natriuretic hormone (206) increases the glomerular filtration rate, diuresis and natriuresis , reduces the movement of signals through the point of departure in the atrial area. It acts at the level of distal portion contort and of the papillary membrane. Quinine , dopamine, prostaglandins also have action in the loss of Na, while angiotensin acts directly and indirectly by stimulating secretion of aldosterone : catecholamines act at proximal and distal contort level. ADH keeps water by acting at the level of contort distal portion and collecting tubes on the interstice space. The electrochemical interaction factors between  Na - proteins act concurrently with oncotic factors, induced by proteins from the blood and the interstice, which control the tubular and peritubular reabsorbtion processes through their anionic groups.

  Glomerular filtration (primary secretion of urine).

At the level of the glomerule  there takes place the formation of the filtered plasma (1/5-1/3 of the  plasma volume) which passes from the glomerular capillaries into the Bowmann Encapsulation. The ultrafiltrate has the same composition as plasma, but without proteins having molecular weight greater than 69,000. Thus a process takes place concentrating proteins in the vascular postglomerular space, having two consequences: (1) exponential increase of colloid – osmotic pressure, (2) absolute increase of the number of anionic protein sites.


Increasing concentrations of protein in the efferent arteriole has a stabilizing role of blood flow. The glomerular flow decreases by clamping the aorta (97) and increases under experimental conditions, by increasing the concentration of protein (albumin) in the blood perfusion (5 - 7%) and intake of hypernatrium. The phenomenon is attributed to the increase of osmotic pressure over 55 mmHg. Protein increase above  10% leads to a non filtering  kidney.


Plasma proteins influence the overall kidney function depending on its status. The increase of concentration of proteins in perfusion of the vasodilatated kidney with acetylcholine changes the effect in the loss on Na  of the protein and decreases the elimination of Na+ and water. The non vasodilated kidney reacts in a variable mode to the increase of the proteic content of infused protein. Protein concentration level stabilizes the glomerular renal circulation and keeps under control the tubular level resorbtion . Patients with analbuminemy (177, 222), protein malnutrition (59, 141) and those with nefrotic syndrome, there is a simultaneous decrease of colloid-osmotic pressure and of fractional Na+ resorption. Increased protein keeps oxygen consumption response decay of glomerular filtration. Albumin increases from 2.5% to 5% and increases absolute resorption of Na+ and water. In the absence of albumin , the kidney eliminets however, 40 - 46% fraction of filtered water and Na+ , i.e  only the minimal regulated fraction of oncotic pressure . Postglomerular decrease in the proteins produces volume expansion and kidney proximal reabsorbtion inhibition of Na+. The mechanisms by which proteins interfere in the regulation of Na+ reabsorbtion can be deciphered taking into account how communication between the three compartments takes place, a process in which oncotic pressure plays an important role. The proteins control reabsorption especially  of Na+ (with their anionic charge). Between Na+ and polyanion protein there are interactions which also definie the  fundamental mechanism of transport of Na+ in the blood (231, 232, 236). In addition to doubling the concentration of proteins in efferent arteriola and peritubular capillaries mention should be made of the richness of anionic groups of interstitial  proteins: serum albumins passed through fenestration of capillaries , mucopolysaccharides rich in anionic groups.


Their numbers increases under the influence of increased quantities of Na+ crossing the interstice and from here into peritubular capillaries , through capillary baseline membrane. The increase of the number of substances removed, obtained by blood dilution, as well as the decrease of glomerular flow , diminishes excretion of sodium also because of the  decrease of concentration of proteins from postglomerular territory. In Henle loop , the Na+ arrested  by proteins, creates the hyperton enviromment necessary for water conservation.

 Tubular reabsorption. The role of proteins.

It is a selective process(248), certain substances being preserved,to keep their blood homeostasis, the so-called threshold substances: glucose, water, electrolytes, aminoacids, etc.. The tubular function is governed by the membranes that separate the three compartments and in particular the composition of proteins, of  vascular and interstitial space. Changes in the intake of any of the substances above are reflected in the composition of urine, fact that  shows that the threshold also depends on the balance


An increased intake of glucose (20%) and a null  intake of Na+ eliminates urine with a high volume, but with an extremely low content of Na+ (data unpublished). Resorption has two phases: the lumen of tubes with its interstition and the latter with the stroke. The exchange between the tubular lumen and interstices achieved in a  paracellular and transcellular mode.Na+, although an extracellular ion, at the level of proximal contorts portion there are  located 20mM/Kg of wet tissue, a content which grows in parallel to  the concentration of the intraluminal filtrate, up to 100m M / Kg , of which 60% is free and 40% held in the cells. Na+ is carried to the interstice on a transcellular route in a rate of 20-25%, endergonic. The paracellular transport is dominant at the Henle loop level, ascending portion, for Na+. The downward branch is impermeable to Na+ but permeable for water. Paracelular transport is made by diffusion. The peritubular environment is hyperosmotic, has a rich content in mucopolysaccharides and basic proteins , serum albumins, rich in anionic groups that interact with Na+.


Na+ resorption at this level is stopped  in the absence of albumins, of subslayers or accelerators with molecular weight between 14,000 and 50,000. In addition, these proteins create the  hyperosmotic environment together with sodium bicarbonate, passed on transcellular pathway, which directs the flow of water. The paracellular pathway of resorption is economical, consumes little energy, (reabsorbed  Na / consumed O2 = 48) for paracellular transportation and equal to 18 for the transcellular). Experimental changing of interstitial environment  decreases Na+ resorption.

        In conclusion, the ureogenetic and homeostasis function of Na+ is performed by special structures (compartiments) and with the variation of blood composition and of glomerular filtrate  along nephron and with an important  role of the proteins. These act by their concentration change , by which they control the colloid - osmotic pressure and also by the richness of anionic charges , interacting with sodium.





[Chapter 5 will be featured in the upcoming January-February 2010 issue of this Journal.]



Professor Marcel Uluitu, M.D. Ph.D. began his scientific activity in Physiology in 1953 at the Physiology School (Medical School) Cluj-Napoca, in Romania. He continued his scientific activity in Physiology in Bucharest at the Institute of Physiology and Pathophysiology Daniel Danielopolu until 2004, at which time he retired as Director of the Institute; he had held this position since 1990. His research work includes studies of the central nervous system physiology relating to the transmission of information in the nervous centers; cerebral excitability, using methods, in their evolution, from the determination on reactive isolated organ, to the most complex physical and chemical methods, in the present. In his research of chemical mediation he studied acetylcholine, serotonin, and their connection with the cerebral metabolism.

Professor Uluitu has also investigated cerebral tissue excitability, studying the structure modification of the protein macromolecules, and the physiological and pathopysiological processes in which are involved Sodium and Lithium. He implemented an original method for physical and chemical processes which involve the chemic active sodium, in normal processes and in the cerebral excitability dysfunctions, in human and in experimental model (animal). These results of this work gave him the chance to outline the chapter herein relating to the physiology of substances transport in the blood. This is based on the physical and chemical interaction between blood components.

His papers are included in the collections of the U.S. National Library of Medicine and the U.S. National Institute of Health. He is a member of the Romanian Academy of Medical Sciences.


Dr. Diana Popa (Uluitu) is a researcher in the Department of Microbiology, Immunology and Molecular Genetics at the University of Kentucky in Lexington, Kentucky, USA. She attended Medical School at Vasile Goldis University in Arad, Romania, and graduated in 1998; during summer breaks at medical school she volunteered at the Institute of Physiology D. Danielopopu in the physiology and microbiology laboratories as well as in the clinic. After completing medical school and a one year internship, she worked as a Research Assistant at the Danielopopu Institute for three years before coming to the University of Kentucky. In addition to her medical thesis, which focused on the actions of Lithium on the central nervous system, since coming to the United States she has published numerous additional papers relating to Lithium and other substances. In continuing her on-going studies, Dr. Popa is currently pursuing a Master’s degree in Public Health at the University of Kentucky. 




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