Biomedical subjects

L W Welling

Publications and source records attributed to L W Welling.

At least 37 records · Page 2Linked to original sources

PubMed1987

Structural and functional comparison of mesonephric and metanephric proximal tubules.

Mesonephric kidneys of the mid-gestation fetus and metanephric kidneys of the adult are known to differ in many gross features but to be qualitatively similar in their cellular morphology. In the present studies, quantitative morphometric and in vitro microperfusion procedures were used to examine further the physical and transport properties of mesonephric and metanephric (S2) proximal tubule segments from rabbit. In perfused mesonephric proximal tubules the volume transport rate was 0.91 +/- 0.08 nl/min per mm tubule length, 2.7 +/- 0.2 nl/min per mm2 basement membrane (outer tubule) surface area, and 0.19 +/- 0.03 nl/min per mm2 basolateral cell membrane surface areas. For comparison, the S2 portion of metanephric proximal tubules is reported to transport 0.33 +/- 0.02 to 0.53 +/- 0.01 nl/min per mm length or, based on the present findings, 2.8 +/- 0.2 to 4.4 +/- 0.8 nl/min per mm2 basement membrane area and 0.16 +/- 0.02 to 0.25 +/- 0.07 nl/min per mm2 basolateral membrane area. Thus, proximal mesonephric and S2 metanephric segments exhibit approximately the same transport per unit area of basement membrane and per unit area of the basolateral cell membranes across which active transport presumably occurs.

Animals↗

PubMed1987

Renal adenocarcinoma and acquired cystic disease in chronic hemodialysis patients.

Three chronic hemodialysis patients developed renal cell adenocarcinoma with evidence of acquired cystic disease in two. The incidence of renal cancer in this study population of 0.27% per year is 50 times greater than that expected in general. The cancers appeared to develop at different rates. In one patient examined by serial computed tomography (CT) over 2.5 years, the tumor progressed rapidly. In the other two patients, the process was more idolent. On the basis of our experience, we recommend that dialysis patients be screened for acquired cystic kidney disease (ACKD) and renal tumors by sonography or CT. Patients with ACKD should be observed at regular intervals by CT for the development of possible tumor.

Adult↗

PubMed1987

Morphometric analysis of distinct microanatomy near the base of proximal tubule cells.

Models of cell shape in the rabbit S2 proximal renal tubule were derived from transmission electron micrographs and compared with scanning micrographs. Standard morphometric procedures were used to measure basolateral cell membrane surface density (SVt) relative to total epithelial volume in numerous zones of cell height. In the basal 20% region we also measured the volume fraction (F) of intercellular spaces and calculated new surface densities in reference only to the intercellular volume, SVi = SVt/F, or to the cellular volume, SVc = SVt/(1-F). Combined use of these surface densities then enabled us to calculate the diameter, length, and separation of effectively cylindrical microvilli at the cell base. Assuming that lateral cell membranes are radially oriented in the apical region but disposed on microvillus like structures of arbitrary orientation at the cell base, an improved cell model was developed that agreed with the scanning picture throughout the entire cell height. Basal microvillar elements contain approximately 60% of the total basolateral cell membrane surface area and possibly constitute a hydrostatic resistive region for absorbate flow. These features have interesting physiological implications.

Animals↗

PubMed1987

Video measurement of basolateral NaCl reflection coefficient in proximal tubule.

Isolated, lumen-collapsed, proximal and distally occluded segments of rabbit S1 and S2 proximal tubule were equilibrated in isotonic NaCl or isosmotic raffinose medium and then exposed acutely to hypotonic or hypertonic raffinose or NaCl solution. The result was a water flux per millimeter tubule length, JVo, across the basolateral cell membranes and a consequent cell swelling or shrinkage that could be measured by a video technique in the initial 0.1 s or less after a change from steady state. The cell volume change was proportional to the applied osmolality difference, delta pi, and differed consistently with the solute employed. From the equation JVo/delta pi = sigma LpA, where sigma is the basolateral membrane reflection coefficient for the osmotic solute used and LpA is the membrane hydraulic conductivity per millimeter tubule length, and from the assumption that sigma raffinose = 1, sigma NaCl was obtained by dividing the JVo/delta pi values from the NaCl studies by those from the raffinose studies. For both S1 and S2 segments, sigma NaCl was found to be approximately 0.5. A similar value was obtained from the rate of cell shrinkage immediately after isosmolar exchange of raffinose for NaCl medium.

Animals↗

PubMed1986

Morphological changes with Na+-free fluid absorption in isolated perfused snake tubules.

Snake (Thamnophis spp.) proximal renal tubules were perfused and bathed in vitro either with medium containing sodium or with medium in which the sodium was replaced with choline. Net fluid absorption was measured by changes in volume marker concentration, and cell volumes and cell membrane surface areas were measured by ultrastructural morphometric methods. Net fluid absorption did not differ significantly in the presence or absence of sodium. However, during the 20-25-min perfusion in the absence of sodium, significant morphological changes took place. The volume of the cells, doubled and the volume of the intercellular spaces nearly quintupled. The areas of the lateral and apical cell membranes approximately doubled, but their surface densities remained essentially constant. Therefore the larger cells in the absence of sodium had proportionally enlarged surface areas, so that the volume-to-surface area ratio remained constant. These morphological changes occurred concomitantly with the maintenance of net fluid absorption and might play a permissive role in such maintenance in the absence of sodium.

Absorption↗

PubMed1986

Basolateral membrane properties of juxtamedullary proximal tubule in newborn rabbit.

We have evaluated the functional and morphological changes that occur in juxtamedullary proximal convoluted tubules before and after the completion of nephrogenesis at approximately 3 wk of age. Tubules were dissected in connection with glomeruli in the deep juxtamedullary zone, crimped at both ends, and induced to swell in isotonic medium by sequential exposure to ouabain, reduced bath protein concentration, and collagenase. Basolateral membrane surface areas were measured morphometrically in paired tubules if possible. The swelling rates and basolateral areas were the same in tubules from 2-7- and 14-17-day-old rabbits (during nephrogenesis), had increased in 28-42-day-old rabbits (after nephrogenesis), and increased further in adults. Because the surface areas and swelling rates increased proportionally, the nephrons "matured" only after nephrogenesis was complete and then only in basolateral surface area. The intrinsic membrane properties of hydraulic conductivity and ion permeability apparently remained constant.

Animals↗

PubMed1986

Use of trypan blue for identifying early proximal convoluted tubules.

Proximal convoluted renal tubules (PCT) are difficult to dissect for in vitro study, particularly in newborn animals, and are identified with certainty only when obtained in continuity with their parent glomeruli. We show here that the supravital colloidal dye trypan blue preferentially stains early PCT segments of rabbit in vivo and greatly facilitates their isolation. We also show that trypan blue administration does not adversely affect animal growth rate, kidney weight, or several general measures of kidney function. Using isolated PCT from newborn to adult rabbits, control (unstained) and trypan blue-stained tubules also are found not to differ in lateral membrane surface density, in their ability to maintain normal cell volume or to respond to hypotonic osmotic challenge, and in their swelling rate in isotonic medium after ouabain treatment. We conclude that trypan blue has no adverse effects on PCT cell function while greatly facilitating their isolation for physiological studies.

Animals↗

PubMed1983

Morphometric comparison of rabbit cortical connecting tubules and collecting ducts.

Connecting tubule (CNT) segments of the rabbit distal nephron were examined by scanning electron microscopy and computer-assisted morphometric analysis of transmission electron micrographs. CNT were very similar to the cortical collecting ducts (CCD) described previously. The epithelium of both segments contains two cell types, both of which can be modeled as simple cuboidal cells, and two distinct systems of extracellular channels. The lateral intercellular channels are comparable to the spaces between simple cuboidal cells but are modified by short projecting microvilli which produce a modest increase in lateral cell surface area. The basal infolded channels are best developed in the connecting tubule cells of CNT and contribute 63% of all channel-associated membranes in CNT. Total membrane areas are similar in CNT and CCD. The two segments differ only in the degree of extracellular channel dilation and the distribution of infolded membrane relative to cell height in the connecting tubule and principal cells. The relatively minor morphometric differences between CNT and CCD do not correlate well with the marked difference in transtubular volume flow induced in the two segments by ADH and an osmotic gradient.

Animals↗

PubMed1983

Basolateral membrane properties in proximal convoluted tubules of the newborn rabbit.

We examined the properties of basolateral cell membranes in "immature" and "mature" proximal tubules and evaluated the possibility that changes in those membranes might contribute to the reported maturation of tubule function. Proximal convoluted tubules were dissected in connection with superficial glomeruli, crimped at both ends, and induced to swell by use of ouabain, low protein bathing medium, and/or collagenase. Tubules from adult animals swelled faster than tubules from 2- to 5- or 14- to 17-day-old animals. However, the basolateral cell membranes of tubules from adult animals were three- to fourfold larger in surface area than those from 2- to 17-day animals, so that the ratio of the swelling rates to the measured basolateral membrane areas remained constant during the period from newborn to adult. We conclude that the basolateral membranes "mature" only in their surface areas and that little change occurs in their intrinsic properties such as hydraulic conductivity or ion permeability.

Aging↗

PubMed1983

Video measurement of basolateral membrane hydraulic conductivity in the proximal tubule.

Isolated, lumen-collapsed S1, S2, and S3 proximal tubule segments from the rabbit were exposed acutely to media made hypotonic or hypertonic by adjusting the concentration of the impermeant solute raffinose. The result was a water flux into or out of the cells across their basolateral cell membranes and a consequent swelling or shrinking of the cells. From tubule volume changes measured at 1/60-s intervals during the first 0.03-0.2 s of video recordings, the earliest water fluxes were found to be 0.76 +/- 0.04 nl X min-1 X mm-1 X mosM-1 in S1, 0.53 +/- 0.03 in S2, and 0.35 +/- 0.04 in S3. When normalized to outer tubule surface areas, these fluxes yield statistically different hydraulic conductivities of about 5,500, 4,000, and 3,000 microns X s-1 in the three segments. However, when normalized to the basolateral membrane surface areas, the basolateral membrane hydraulic conductivities are all approximately 300 microns X s-1 and not statistically different. If one assumes that the hydraulic conductivities of the basolateral and apical cell membranes are equal, the latter value agrees with reported transtubular measurements and is sufficient to allow nearly isotonic transcellular absorption to occur with driving forces of 2-3 mosM.

Animals↗

PubMed1983

Localization of tissue potassium pools in the amphibian kidney.

Techniques were developed to determine the location of exchangeable K pools that had been identified previously in kinetic studies of the intact perfused bullfrog kidney. Following perfusion of the kidneys with 42K, a washout of the isotope was begun and interrupted at various times; the kidneys were removed, frozen, dried at low pressure and temperature, and then microdissected. Glomerular capillary tufts, small segments of tissue containing early distal tubules (diluting segment), and other segments containing proximal tubular convolutions were removed and analyzed for total content of K and 42K. In the intact kidney 77% of tissue K exchanged in 60 min. The exchangeable K concentration was 95 mu eq/ml cell water. Correction for the K activity coefficient in Ringer solution yielded an activity of 72 mu eq/ml. Thirty-two percent of glomerular capillary K exchanged in 60 min; 7% exchanged with a half time of 3.5 min; and the remainder exchanged at a rate too slow to measure. The data from tissue containing proximal tubular segments were too scattered to permit analysis. In segments containing early distal tubules, 67% of tissue K was contained in two exchangeable pools: one pool exchanged at a rate 10-fold greater than did the other. The data for these two distal pools were analyzed in terms of a parallel model (two cell types?) and a nested model (cytoplasm and subcellular organelles?). Pool size and exchange rates were calculated for both models. Electron microscopic analysis revealed that early distal tubular segments contain only one cell type which has a large population of mitochondria. This suggests that the nested model is more plausible. The fast distal pool exchanged at the same rate as the fast-exchanging pool identified in kinetic studies of the intact functioning kidney and is considered to be the K secretory pool.

Animals↗

PubMed1981

Shape of cells and extracellular channels in rabbit cortical collecting ducts.

Superficial cortical collecting ducts of rabbits were examined by scanning electron microscopy and by computer-assisted morphometric analysis of transmission electron micrographs. The epithelium contains two cell types, principal and intercalated, which have similar surface concentrations for apical and basal cell membranes and which can be modeled as simple cuboidal cells. The epithelium also contains two distinct and markedly different systems of extracellular channels. One system, the lateral intercellular channels, is comparable to the spaces between simple cuboidal cells but is modified by laterally projecting microvilli and ridges that produce a 1.8-fold magnification of the lateral cell surfaces. Those surfaces are nearly identical in the two cell types and constitute 38% of all cell membranes facing extracellular channels. The other channel system, the basal infolded channels, is well developed only in the basal 40% of principal cells and constitutes 62% of all channel-associated membrane. Its unique feature is an exponential increase in surface area, which is reminiscent of all channel-associated membranes in proximal nephron segments and which can be modeled as the interdigitation of cellular leaflets entirely within the boundaries of single cells.

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↗

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↗