Functional characteristics of peritubular capillary membrane in rat kidney

1987 ◽  
Vol 253 (1) ◽  
pp. F180-F187 ◽  
Author(s):  
M. Larson ◽  
K. Nygren ◽  
M. Sjoquist ◽  
M. Wolgast
Keyword(s):  
Pore Radius ◽  
Rat Kidney ◽  
Molecular Probes ◽  
Peritubular Capillary ◽  
Equivalent Radius ◽  
Fluid Reabsorption ◽  
Pore Length ◽  
Capillary Membrane ◽  
Small Pore ◽  
Pore Area

The permeability characteristics of the peritubular capillary membrane in the rat kidney were investigated on the basis of the transport of hippuran, inulin, myoglobin, horseradish peroxidase, albumin, and gamma-globulin from peritubular capillary blood to renal hilar lymph. Data obtained in a previous investigation on single-nephron plasma flow, filtration fraction, net driving force, and fluid reabsorption along the peritubular capillary were also used. The data were analyzed in a computer-based model taking into account the transport both by diffusion and by convection. The results show that the membrane contains a few large pores through which the plasma proteins leak out into the renal interstitium and a system of several smaller pores responsible for the fluid reabsorption. The mean equivalent radius of the large pores was estimated from the larger molecular probes to be approximately 180 A (range 150-225 A), and the corresponding total pore area over pore length was estimated at 3 X 10(-4) cm (range 6 X 10(-4) to 1 X 10(-4) cm). The small-pore system was analyzed from the transport of hippuran, inulin, and myoglobin and from fluid reabsorption and showed a pore radius of somewhat below 20 A and pore areas over pore length of 50 cm. Here, the fluid reabsorption and the transport of hippuran turned out to be a sensitive marker of the pore area and the transport of inulin and myoglobin of the pore radius.

Renal cortical interstitium and fluid absorption by peritubular capillaries

1994 ◽  
Vol 266 (2) ◽  
pp. F175-F184 ◽  
Author(s):  
K. Aukland ◽  
R. T. Bogusky ◽  
E. M. Renkin
Keyword(s):  
Rat Kidney ◽  
Colloid Osmotic Pressure ◽  
Capillary Wall ◽  
Peritubular Capillary ◽  
Fluid Reabsorption ◽  
Fluid Uptake ◽  
Peritubular Capillaries ◽  
Capillary Fluid ◽  
Renal Cortical Interstitium ◽  
Relative Retardation

Every minute, the cortical peritubular capillaries in a 1-g rat kidney take up more than 0.5 ml tubular reabsorbate. Studies of renal lymph and measurements of pressure in capillaries (Pc) and interstitium (Pi) indicate that normally the protein colloid osmotic pressure of peritubular capillary plasma (COPp) provides the necessary absorptive force, keeping Pi at 2-4 mmHg, i.e., 8-10 mmHg lower than Pc. At reduced COPp, continued delivery of fluid from the tubules automatically raises Pi to maintain capillary fluid uptake. The transient Pi response to sudden exposure of the kidney to subatmospheric pressure shows that such adjustment of forces may take place in only 5 s. Most remarkable, adjustment of forces may take place in only 5 s. Most remarkable, reabsorption continues during protein-free perfusion of the isolated rat kidney, apparently effected by a Pi exceeding Pc. A relative retardation of interstitial uptake of ferritin from plasma in this case suggests fluid reabsorption through both small and large pores in the capillary wall. Collapse of the capillaries is presumably prevented by tight tethering to the capillary wall, giving the narrow interstitium a very low compliance.

A distributed two-pore model: theoretical implications and practical application to the glomerular sieving of Ficoll

2014 ◽  
Vol 306 (8) ◽  
pp. F844-F854 ◽  
Author(s):  
Carl M. Öberg ◽  
Bengt Rippe
Keyword(s):  
Pore Radius ◽  
Diffusion Length ◽  
Wide Distribution ◽  
Analytic Solutions ◽  
Length Ratio ◽  
Pore Sizes ◽  
Filtration Barrier ◽  
Large Pore ◽  
Small Pore ◽  
Pore Area

In the present study, an extended two-pore theory is presented where the porous pathways are continuously distributed according to small- and large-pore mean radii and SDs. Experimental glomerular sieving data for Ficoll were analyzed using the model. In addition, several theoretical findings are presented along with analytic solutions to many of the equations used in distributed pore modeling. The results of the data analysis revealed a small-pore population in the glomerular capillary wall with a mean radius of 36.6 Å having a wide arithmetic SD of ∼5 Å and a large-pore radius of 98.6 Å with an even wider SD of ∼44 Å. The small-pore radius obtained in the analysis was close to that of human serum albumin (35.5 Å). By reanalyzing the data and setting the distribution spread of the model constant, we discovered that a narrow distribution is compensated by an increased mean pore radius and a decreased pore area-to-diffusion length ratio. The wide distribution of pore sizes obtained in the present analysis, even when considering electrostatic hindrance due to the negatively charged barrier, is inconsistent with the high selectivity to proteins typically characterizing the glomerular filtration barrier. We therefore hypothesize that a large portion of the variance in the distribution of pore sizes obtained is due to the molecular “flexibility” of Ficoll, implying that the true variance of the pore system is lower than that obtained using flexible probes. This would also, in part, explain the commonly noted discrepancy between the pore area-to-diffusion length ratio and the filtration coefficient.

Role of luminal hydrostatic pressure in proximal tubular fluid reabsorption in the rat

1975 ◽  
Vol 229 (3) ◽  
pp. 813-819 ◽  
Author(s):  
A Grandchamp ◽  
Scherrer ◽  
D Scholer ◽  
J Bornand
Keyword(s):  
Hydrostatic Pressure ◽  
Proximal Tubule ◽  
Pressure Difference ◽  
Unit Area ◽  
Rat Kidney ◽  
Fluid Reabsorption ◽  
Proximal Tubular ◽  
Tubular Fluid Reabsorption ◽  
Selective Change

The effect of small changes in intraluminal hydrostatic pressure (P) on the tubular radius (r) and the net fluid reabsorption per unit of surface area of the tubular wall (Js) has been studied in the proximal tubule of the rat kidney. The split-drop method was used to simultaneously determine Js and r. Two standardized split-drop techniques A and B allow selective change in P. P was 31.6 +/- 1.3 mmHg in technique A and 15.5 +/- 1.5 in technique B. The pressure difference significantly affected the tubular radius; r was 21.9 +/- 0.4 and 18.6 +/- 0.5 mum in the split drop A and B, respectively. In contrast, net transepithelial fluid reabsorption Js was unchanged. Js amounted to 2.72 +/- 0.20, and 2.78 +/- 0.33 10(-5) cm3 cm-2 s-1 in split drop A and B. The absence of variations in Js could result from two opposite effects of pressure. P might enhance Js by increased ultrafiltration. However, the rise in r might decrease the density of the intraepithelial transport paths per unit area of tubular wall and therefore might decrease Js.

Hydrophilic solute transport across rat alveolar epithelium

1989 ◽  
Vol 66 (5) ◽  
pp. 2320-2327 ◽  
Author(s):  
M. M. Berg ◽  
K. J. Kim ◽  
R. L. Lubman ◽  
E. D. Crandall
Keyword(s):  
Water Flow ◽  
Alveolar Epithelium ◽  
Lavage Fluid ◽  
Alveolar Space ◽  
Apparent Permeability ◽  
Diffusive Flow ◽  
Permeability Surface ◽  
Small Pore ◽  
Pore Area ◽  
Flow Through

Diffusional fluxes of a series of hydrophilic nonelectrolytes (molecular radii ranging from 0.15 to 0.57 nm) were measured across the alveolocapillary barrier in the isolated perfused fluid-filled rat lung. Radiolabeled solutes were lavaged into the distal air spaces of isolated Ringer-perfused lungs, and apparent permeability-surface area products were calculated from the rates of isotope appearance in the recirculating perfusate. These data were used to estimate theoretical equivalent pore radii in the alveolar epithelium, with the assumption of diffusive flow through water-filled cylindrical pores. The alveolar epithelium is best characterized by two pore populations, with small pores (radius 0.5 nm) occupying 98.7% of total pore area and larger pores (radius 3.4 nm) occupying 1.3% of total pore area. Net water flow out of the alveolar space was measured by including an impermeant solute (dextran) in the lavage fluid and measuring its concentration in the alveolar space as a function of time. Under control conditions, net water flow averaged 167 nl/s. When 24 microM terbutaline was added to the perfusate, net water flow increased significantly to 350 nl/s (P less than 0.001). Terbutaline had no effect on the fluxes of either glycerol (which traverses the small pore pathway) or sucrose (which traverses the large pore pathway). These findings indicate that the intact mammalian alveolar epithelium is complex and highly resistant to the flow of solutes and water.

Macromolecular transport in canine coronary microvasculature

1990 ◽  
Vol 258 (3) ◽  
pp. H748-H753 ◽  
Author(s):  
C. F. Pilati
Keyword(s):  
Total Protein ◽  
Filtration Rate ◽  
Volume Flow ◽  
Solute Flux ◽  
Base Line ◽  
Pore System ◽  
Plasma Protein Concentration ◽  
Equivalent Radius ◽  
Macromolecular Transport ◽  
Small Pore

Coronary vascular osmotic reflection coefficients (sigma dS) for total protein, albumin (Alb), immunoglobulin (Ig)G, and IgM were determined in the anesthetized dog. Myocardial lymph was collected from the anterior interventricular lymphatic trunk, and the sigma dS estimated from filtration rate-independent lymph-to-plasma protein concentration ratios (CL/CPS). Lymph flows of at least 12 times base line were needed to produce filtration rate-independent CL/CPS, and these were achieved in 9 of 12 experiments. In these nine experiments, sigma dS for total protein, Alb, IgG, and IgM were, respectively, 0.67 +/- 0.02 (SE), 0.59 +/- 0.05, 0.70 +/- 0.03, and 0.87 +/- 0.01. The data were fitted to a model that showed that transvascular fluid and solute flux could be described by two populations of pores. A large pore system with an equivalent radius of 235 A was responsible for 39% of the transvascular volume flow. A small pore system less than 53 A accounted for the remaining flow. In a second group of experiments (n = 8), 60 min of ischemia decreased the sigma dS to 0.27 +/- 0.03, 0.07 +/- 0.05, 0.22 +/- 0.03, and 0.69 +/- 0.04 for total protein, Alb, IgG, and IgM, respectively. A single population of pores of 220 A could describe the entire transvascular volume flow. These results indicate that coronary vascular protein permeability is moderately high and can be increased significantly by ischemia.

scholarly journals Measurement of the Permeability of Biological Membranes Application to the glomerular wall

1973 ◽  
Vol 62 (4) ◽  
pp. 489-507 ◽  
Author(s):  
A. Verniory ◽  
R. Du Bois ◽  
P. Decoodt ◽  
J. P. Gassee ◽  
P. P. Lambert
Keyword(s):  
Poiseuille Flow ◽  
Path Length ◽  
Pore Radius ◽  
Frictional Resistance ◽  
Theoretical Studies ◽  
Equivalent Radius ◽  
A Value ◽  
Anesthetized Dogs ◽  
The Mean ◽  
Diffusion And Convection

The transport equation describing the flow of solute across a membrane has been modified on the basis of theoretical studies calculating the drag of a sphere moving in a viscous liquid undergoing Poiseuille flow inside a cylinder. It is shown that different frictional resistance terms should be introduced to calculate the contributions of diffusion and convection. New sieving equations are derived to calculate r and Ap/Δx (respectively, the pore radius and the total area of the pores per unit of path length). These equations provide a better agreement than the older formulas between the calculated and the experimental glomerular sieving coefficients for [125I]polyvinylpyrrolidone (PVP) fractions with a mean equivalent radius between 19 and 37 Å. From r and Ap/Δx, the mean effective glomerular filtration pressure has been calculated, applying Poiseuille's law. A value of 15.4 mm Hg has been derived from the mean sieving curve obtained from 23 experiments performed on normal anesthetized dogs.

A Study in Vivo of Peritubular Oncotic Pressure and Proximal Tubular Reabsorption in the Rat

1976 ◽  
Vol 51 (4) ◽  
pp. 379-392 ◽  
Author(s):  
J. D. Conger ◽  
E. Bartoli ◽  
L. E. Earley
Keyword(s):  
Tubular Reabsorption ◽  
Detectable Effect ◽  
Oncotic Pressure ◽  
Peritubular Capillary ◽  
Fluid Reabsorption ◽  
Proximal Tubular ◽  
Convoluted Tubules ◽  
Proximal Tubular Reabsorption ◽  
Tubule Fluid

1. Peritubular capillary microperfusion was used to examine the effects of protein-free and hyperoncotic homologous plasma on fluid reabsorption by proximal convoluted tubules in the hydropenic rat. 3H-labelled p-aminohippurate was added to perfusates for the purpose of estimating the extent to which tubules under study were bathed by the perfusates. [14C]Mannitol was added to perfusates in order to detect contamination of collected tubular fluid by perfusates. 2. Hydrostatic pressures were monitored in the peritubular microvasculature and adjacent proximal tubules during perfusion. Evidence for secretion of p-aminohippurate from perfusate into tubules under study was determined by collecting tubular fluid from both early and late puncture sites. Fractional and absolute reabsorption were not affected by either the protein-free or the hyperoncotic plasma. 3. When acetazolamide was added to the perfusate both fractional and absolute reabsorptive rates decreased by an average of 36%, indicating that the techniques were capable of detecting a decrease in proximal tubular reabsorption. 4. It is concluded that under the conditions of this study changes in peritubular capillary protein concentrations have no detectable effect on the rate of proximal convoluted tubule fluid reabsorption.

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