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Biomedical subjects

D J Welling

Publications and source records attributed to D J Welling.

13 recordsLinked to original sources
PubMed1992

Measurement of albumin reflection coefficient with isolated rat glomeruli.

Macromolecular permeability of the glomerular capillary has been inferred from the clearance of endogenous protein or infused macromolecules. Permeability is increased after treatment with polycations as well as after renal injury. It has previously been shown that the capillaries of glomeruli isolated from normal mammals expand or collapse in response to transcapillary albumin gradients and that the magnitude of the changes in capillary volume and in total glomerular volume are directly proportional to the applied oncotic gradients. In the experiments presented here, the volume responses of control glomeruli and of glomeruli treated with protamine (100 to 600 micrograms/mL for up to 60 min) were used to calculate the albumin reflection coefficient, sigma albumin, and the convectional permeability, P convectional albumin = (1 - sigma albumin), of the capillary wall. Sigma albumin for normal glomeruli was about 1 (P convectional albumin = 0); sigma albumin fell to a minimum of 0.2 +/- 0.1 (P convectional albumin = 0.8 +/- 0.1) after incubation with protamine sulfate (600 micrograms/mL) for 30 min. Retraction and fusion of podocyte foot processes and denudation of the underlying matrix was seen on scanning electron micrographs of protamine-treated glomeruli. These results confirm that it is possible to study macromolecular permeability of the glomerular capillary in vitro and to calculate sigma albumin independent of hemodynamic and systemic humoral influences. This method will permit the assessment of the effects of individual mediators of glomerular injury and the study of glomeruli from kidneys affected by experimentally induced or naturally occurring renal diseases.

Albumins↗
PubMed1979

Effects of ouabain on potassium transport in the perfused bullfrog kidney.

We studied the effect of ouabain on transepithelial and cellular potassium transport in the isolated perfused bullfrog kidney. We used recently developed techniques for estimating the unidirectional reabsorptive and secretory K fluxes (Jr and Js) and measuring the kinetics of cellular K transport. Two hours of perfusion with 1 X 10(-6) M ouabain did not affect GFR, reduced fractional Na reabsorption 57%, increased K excretion 41%, and inhibited Jr 34%. Js rose 68% at 60 min and then returned to the control level. Ninety minutes of perfusion with 5 X 10(-6) M ouabain reduced GFR 28% and fractional Na reabsorption 76%. K excretion rapidly increased 71% within 30 min and then fell to 60% of the control level, while Jr fell 64%. Js rose 42% in 30 min and then fell to 23% of the control level. Both doses reduced K uptake into cellular pools from the circulation and increased the rate coefficients for efflux into tubular fluid. The data indicate that ouabain inhibited reabsorption and transiently accelerated the rate of loss of K from the cells into the tubular fluid. This initially masked the ultimate inhibition of K secretion from the circulation into the tubular fluid.

Animals↗
PubMed1979

Computer-assisted morphometric analysis for three-dimensional cell shape.

Quantitative, morphometric analysis of 3-dimensional cell shape may prove to be a valuable adjunct to scanning electron microscopy and to the evaluation of epithelial transport phenomena. Therefore, to facilitate the wider use of cell shape analysis, a computer-assisted technique has been developed to supplement or replace the usually tedious and otherwise limited manual techniques previously available. The computer programs described here have been designed to run in a small laboratory computer, do not require a large amount of operator time, and are shown to provide an accuracy and efficiency not practical with manual procedures.

Animals↗
PubMed1979

Cell shape as an indicator of volume reabsorption in proximal nephron.

If the complex shape of cells and intercellular channels in the renal proximal tubule is determined in part by the forces of large transepithelial water flow, the cell and channel shapes might serve as indicators of the type and magnitude of the forces required for water flow and the routes of that flow. We review here the known morphologic and functional data from the convoluted and straight portions of the rabbit proximal tubule and test the hypothesis of structure-function correlation in that tissue by means of a mass balance equation. If the lateral cell walls are sufficiently deformable to communicate small transmembrane differences in hydrostatic pressure, the resulting phenomenological model suggests an important new role for peritubular serum proteins and can be used to compute reasonable values for cell wall hydraulic conductivity, intercellular protein diffusion constant, and a channel fluid osmolality not more than 1% greater than that of luminal fluid. We conclude that quantitative morphologic studies may serve as a powerful means for evaluating and understanding transport phenomenons in the nephron.

Animals↗
PubMed1978

Shape of cells and intercellular channels in rabbit thick ascending limb of Henle.

Electron micrographs of cortical thick ascending limb of Henle (TALH) were studied using morphometric techniques. The apical cell surface and the tubule basement membrane have identical areas of 0.8 x 10(5) mu2/mm of tubule length in a typical tubule (I.D. = 15 mu, O.D. = 25 mu). The total area of lateral cell walls bordering intercellular channels in 7.9 x 10(5) mu2/mm of typical tubule, and the ratio of apical cell surface to lateral surface in 0.10 +/- 0.01. When the photographed tubule mass was divided into five concentric zones of equal thickness, the lateral wall areas per zone were found to increase more rapidly than exponential, from 0.63 x 10(5) mu2/mm in that zone nearest the lumen to 3.6 c 10(5) mu2/mm in that zone adjacent to basement membrane. From these data and the estimated number of cells per mm of tubule length (764 cells), the circumferences of individual cells could be calculated for each zone, and quantative three-dimensional cell model could be constructed. The shape of intercellular channels is similar to that of the space between concentric, truncated, and plated horns. TALH cells are compared to previously described cells of rabbit proximal convoluted and straight tubules.

Animals↗
PubMed1978

Physical properties of isolated perfused basement membranes from rabbit loop of Henle.

Isolated, perfused segments of late proximal straight tubule, descending thin limb of Henle, and ascending thick limb of Henle from the rabbit were studied before and after removal of the epithelium with sodium deoxycholate. The relationship between transmural hydrostatic pressure and outer tubule diameter was similar in paired intact tubules and basement membranes, indicating that basement membrane is the principal determinent of tubule distensibility. As calculated from teh measured perfusate flow at several different transmembrane hydrostatic pressures, the hydraulic conductivity of the basement membranes was 6-8 X 10(-3) cm3/cm2.min.cmH2O. With use of these LP values and the calculated oncotic pressure required experimentally to reduce transmembrane hydrostatic pressure transiently to zero, the apparent reflection coefficient of the basement membranes for serum albumin was estimated to be 0.05-0.16. It is concluded that basement membranes of the loop and of other previously studied segments of rabbit nephron provide very strong and elastic mechanical support to the epithelium while having minimal resistance to flow of water and of solutes as large as serum albumin.

Animals↗
PubMed1978

Phenomenological model relating cell shape to water reabsorption in proximal nephron.

If the complex pattern of intercellular channels in proximal tubule is determined in part by the forces of large transepithelial water flow, the shape of the cells is an indicator of the type and magnitude of the forces required for water movement and the routes of that flow. To test this thesis, morphologic data and volume flow parameters for rabbit proximal tubule are related generally by a mass balance equation. If the intercellular boundaries are assumed to be highly deformable and to respond to changes in hydrostatic pressure, the solution to that equation is a simple relationship between cell shape and the forces required for water movement. The resulting phenomenological model suggests an important new role for peritubular serum proteins and can be used to compute reasonable values for cell wall hydraulic conductivity, intercellular protein diffusion constant, and a channel fluid osmolality not more than 1% greater than that of luminal fluid. It is concluded that quantitative morphologic studies may serve as a powerful means for evaluating and understanding transport phenomena in the nephron.

Biological Transport↗
PubMed1978

Potassium reabsorption and secretion in the perfused bullfrog kidney.

Techniques have been developed for obtaining comparative estimates of the rates of K secretion and reabsorption in the artificially perfused bullfrog kidney and the use of 42K infused into the portal circulation. In control experiments in which Kexc/Kfilt averaged 0.65, approximately 30% of filtered K escaped reabsorption and excreted K was composed of roughly equal parts of filtered K and secreted K. Fractional reabsorption of K was constant at 70% over a wide range of filtration rates. The rate of K secretion correlated significantly with the rate of Na reabsorption and with the urine flow rate. Acetazolamide stimulated secretion and inhibited reabsorption.

Acetazolamide↗
PubMed1977

Kinetic analysis of potassium transport in bullfrog kidney.

Techniques have been developed for studying the distribution and the rates of exchange of K among urine, the tubular cells, and the circulation in the isolated, pump-perfused, bullfrog kidney. Tubular cells were loaded with 42K via the portal circulation, and the subsequent washout of the tracer into the vena cava and into urine was measured. Analysis of the data indicated the existence of at least three cellular pools of K. Pools a and b have half times of exchange of 1.1 and 4.1 min and contain about 25 and 40% of tissue K, respectively. The remainder of cellular K is contained in one or more very slowly exchanging pools. The rate of exchange of K at the basolateral surface of tubular cells is 50-fold greater than at the luminal surface. A pulse-washout method was also devised to permit control and experimental measurements to be made in the same kidney. With this technique, we found that portal perfusion with 10 mM K increased the rate of uptake into pools a and b from the circulation and the rate constants for efflux into the urine from both pools, Acetazolamide increased uptake into pool a and the rate constants for efflux into the urine from both pools.

Acetazolamide↗
PubMed1976

Shape of epithelial cells and intercellular channels in the rabbit proximal nephron.

In electron micrographs of proximal convoluted (PCT) and proximal straight tubules (PST), epithelial height was divided into five zones of equal thickness. Morphometric techniques were used to calculate surface area of cell wall bordering intercellular channels in each zone. Surface concentration of total lateral cell surface is 3.85 mu2/mu3 of PCT and 2.90 mu2/mu3 of PST. For tubules normalized to outer diameter = 40mu and inner diameter = 25mu, total lateral area is 29 X 10(5) mu2/mm of PCT and 22 X 10(5) mu2/mm of PST. Zone 5 adjacent to basement membrane has similar area (congruent to 17 X 10(5) mu2/mm) and fine structure in PCT and PST. However, the luminal four-fifths of the two cells differ markedly. Lateral area in PCT zones 1 through 4 increases approximately exponentially (from 1.1 X 10(5) to 6.4 X 10(5) mu2/mm) and constitutes 44% of total area. Respective areas in PST increase at a rate greater than exponential (from 0.7 X 10(5) to 2.6 X 10(5) mu2/mm) but constitute only 23% of total. From these data and the estimated number of cells per millimeter of tubule (825), circumferences of individual cells were estimated and quantitative three-dimensional cell models were constructed. The shape of intercellular channels is similar to that of the space between concentric, truncated and pleated horns.

Animals↗
PubMed1975

Surface areas of brush border and lateral cell walls in the rabbit proximal nephron.

A morphometric technique is used to estimate the absolute and relative surface areas of the brush border microvilli and cell walls bordering lateral intercellular spaces. In isolated, perfused proximal tubule from rabbit, the luminal and lateral surfaces are equal in area. For proximal convoluted tubules (PCT) each surface is 4.1 +/- 0.3 mu2/mu3 of epithelial cell volume or approximately 2.9 X 10(6) mu2/mm of tubule length. In proximal straight tubules (PST) the areas are 2.6 +/- 0.2 mu2/mu3 or 1.2 X 10(6) mu2/mm. Brush border enlarges the apical cell surface 36-fold in PCT and 15-fold in PST. The luminal and lateral cell surfaces each are approximately 20-fold (in PCT) and 10-fold (in PST) greater than the areas of the basal cell surface and tubule basement membrane. These data may be important in the context of an intercellular transport model.

Animals↗
PubMed1975

Pressure-flow-diameter relationships in isolated perfused thin limb of Henle.

To measure directly the relationships between flow rate, tubule diameter, and flow resistance in thin descending limbs of Henle, isolated tubule segments from the rabbit were studied by in vitro microperfusion. Small increases in pressure and flow cause rapid enlargement of the tubule. Flow resistance is inversely related to tubule diameter and, by its effect on transmural pressure, indirectly limits the extent of tubule dilation. In a range of transmural pressures comparable to that in vivo, the tubule is capable of radial dilations as great as 35% and does not reach its structural limit of distensibility. Flow resistance may be approximately by a Poiseuille equation for cylindrical tubules. The effective luminal diameter is approximately a constant fraction of outer tubule diameter and is defined approximately by the innermost projection of semirigid epithelial nuclei.

Animals↗