Biomedical subjects

L W Welling

Publications and source records attributed to L W Welling.

At least 19 recordsLinked to original sources

PubMed1991

Role of cytoskeleton in isotonic cell volume control of rabbit proximal tubules.

Stability of mammalian cell volume depends primarily on the sodium pump. When active cation transport of rabbit renal proximal tubules is blocked by ouabain, cells swell, but their size is limited by residual volume control mechanisms. This "ouabain-resistant" volume control is not an active process, as it operates in the presence of cyanide and dinitrophenol and in the absence of exogenous energy. Nevertheless, it remains incompletely explained by known transmembrane oncotic and hydrostatic forces. We tested the hypothesis that the cytoskeleton contributes to isotonic cell volume control. Isolated, collapsed rabbit proximal convoluted tubules (PCT) were crimped at both ends with micropipettes and had their volume assessed optically. PCT in ouabain (1 mM) swelled to 1.40 above control with protein, 1.62 without protein, and 1.89 with the cytoskeleton inhibitors vincristine (5 microM) and cytochalasin B (50 microM) and without protein. Tubulozole-C and cytochalasin D gave similar results. A hydrostatic pressure of 50 cmH2O increased tubule volume to 1.93 before the tubule basement membrane (TBM) prevented further volume increase. We conclude that volume of renal tubule cells in ouabain is limited partly by external protein, but primarily by the cytoskeleton. The TBM prevents massive swelling and tubule disaggregation.

Animals↗

PubMed1991

Arginine vasopressin stimulates net fluid secretion in a polarized subculture of cyst-forming MDCK cells.

Transepithelial fluid secretion is an important process in the progressive enlargement of certain types of renal cysts. Arginine vasopressin (AVP) increases the rate of cyst formation and expansion in an in vitro model of renal cysts that uses Madin-Darby canine kidney (MDCK) cells grown in a gelled matrix of Type 1 collagen. In this study, it was determined if AVP promoted net fluid secretion by MDCK cells. The rate of volumetric fluid secretion was determined from the net movement of water across epithelial layers of MDCK cells grown on permeable, collagen-coated membranes. AVP in the basolateral medium (but not in apical medium) at concentrations exceeding 10(-9) M caused sustained basolateral to apical transepithelial fluid secretion (approximately 0.6 microL/cm2/h). 1-Desamino-8-D-AVP, a V2 receptor agonist, had a similar effect. The secreted fluid was hyperosmotic compared with the bath (5.7 to 9.7 mosM). Chloride was consistently secreted, but the absolute level in the secreted fluid was variable. Intracellular cAMP content was increased 187% by a 2-h exposure to AVP and 10(-4) M methylisobutylxanthine. Net fluid secretion was augmented by methylisobutylxanthine and theophylline and was inhibited by ouabain, bumetanide, and a sodium-dependent Cl-/HCO3- exchange inhibitor (L-645,695) but was not altered by clonidine, guanabenz, or indomethacin. AVP-induced fluid secretion was not accompanied by a change in transepithelial hydraulic conductivity. It is suggested that AVP stimulates fluid secretion of MDCK epithelial monolayers by activating V2 receptor-mediated adenylate cyclase. The regulation of net fluid secretion by AVP would appear to depend on modulation of solute transport, rather than on water permeability.

Animals↗

PubMed1990

Relative osmotic effects of raffinose, KCl, and NaCl across basolateral cell membrane.

Lumen-collapsed segments of rabbit S2 proximal tubule were bathed in isotonic medium and then exposed acutely to a medium made hypertonic by the addition of raffinose, NaCl, KCl, Na gluconate, K gluconate, or choline Cl. The result was a rapid efflux of water and a shrinking of the tubule, which could be measured by video techniques within the first 0.1 s. After reequilibration in isotonic medium, each tubule was then exposed to a second hypertonic medium to provide a direct comparison between two different solutes, either NaCl vs. KCl or raffinose vs. any one of the other solutes. Because raffinose is impermeant across the basolateral cell membrane, the ratio of its effect to that of another solute is a measure of the reflection coefficient (sigma) of that other solute. The following results were obtained: sigma KCl = 0.70 +/- 0.02, sigma K gluconate = 0.97 +/- 0.07, sigma Na gluconate = 0.84 +/- 0.06, and sigma choline Cl = 0.75 +/- 0.06. We previously have reported sigma NaCl = 0.56 +/- 0.07. If sigma of each salt is considered to be the arithmetic average of its component parts, and if gluconate and choline are considered to be impermeant, we also obtain sigma Na+ = 0.68, sigma K+ = 0.94, and sigma Cl- = 0.50.

Animals↗

PubMed1990

Prediction of carcinoma in acquired cystic disease as a function of kidney weight.

Acquired renal cystic disease occurs in up to 80% of patients on chronic dialysis and is complicated by renal adenocarcinoma in about 6% of cases. This report suggests that acquired cystic kidneys weighing more than 150 g are six times more likely to contain carcinoma than are kidneys of smaller size. This relationship is true whether or not the large kidney contains a radiologically detectable tumor. Therefore, even in the absence of demonstrable tumor mass, strong consideration should be given to the removal of large acquired cystic kidneys.

Carcinoma, Renal Cell↗

PubMed1989

Renal tubular differentiation in mouse and mouse metanephric culture. I. Ultrastructural studies.

We studied the morphologic features of renal tubular differentiation in transfilter metanephric culture. Differentiation of portions of the S-shaped loop into proximal convoluted tubule was detected shortly after 72 h of culture by the appearance of microvilli, coated membrane invaginations, and an apical vacuolar-microtubular network. These features developed synchronously, and the microvilli became progressively more numerous and more compact to form a brush border. Computer-assisted morphometric analysis showed only minor differences between proximal tubular cells from 18-day embryos and tubular cells from 7-day cultures of blastema taken from 11-day embryos. Segments of tubule corresponding to distal convoluted tubules were lined with relatively simple cells that contained few differentiating characteristics. Morphometric modeling of the tubular cells indicated a simple shape consistent with an inherent transport function.

Animals↗

PubMed1989

Renal tubular differentiation in mouse and mouse metanephric culture. II. Na-K-ATPase activity.

Sodium-potassium adenosine triphosphatase (Na-K-ATPase) activity was measured by microassay, and the surface density of basolateral membranes was measured morphometrically in postglomerular segments of single tubules isolated from normally developing, intact mouse kidneys and from transfilter metanephric cultures. Proximal tubule Na-K-ATPase activity was 1092 +/- 480 pmol/mm per hour in newborn mice, increasing to 2462 +/- 258 in 1-week-old and 3470 +/- 578 pmol/mm per hour in adult mice. The Na-K-ATPase activity in newborn mice was approximately one-third of the activity in adult mice. Tubular Na-K-ATPase in transfilter metanephric culture was 972 +/- 536 pmol/mm per hour, a mean value almost identical to that in newborn mice. The surface density of basolateral cell membranes was 1.36 +/- 0.60 microns2/microns3 in newborn mice and 1.34 +/- 0.45 microns2/microns3 in 1-week-old mice, increasing to 2.70 +/- 0.98 microns2/microns3 in 4-week-old mice and 2.89 +/- 0.51 microns2/microns3 in adult mice. The surface density of tubular basolateral cell membranes in transfilter metanephric culture was 1.13 +/- 0.51 microns2/microns3, not significantly different from the surface density in newborn mice. The calculated mean surface area of basolateral membranes per unit tubular length was greater in cultures than in newborns, however, because total epithelial volume per unit length was significantly larger in the cultured tubules. Membrane surface area in intact mice increased with age, the surface area per unit length of tubule in adults being 4.6 times the area in newborn animals.(ABSTRACT TRUNCATED AT 250 WORDS)

Aging↗

PubMed1989

Intestinal transport in megacolonic mice. Alterations in sugar absorption.

This study examined jejunal sugar absorption in piebald mice with congenital megacolon and in normal littermates. Transmural potential difference, short-circuit current, and tissue conductance of flat sheets of jejunum set up in flux chambers were significantly greater in the diseased mice compared to normal siblings. In piebald mice, net absorption of 3-o-methylglucose was enhanced due to a significant increase in mucosal-to-serosal flux compared with normal littermates. Stimulation of electrogenic sodium absorption by alanine (10 mM) increased basal short-circuit currents more in piebald tissues than in tissues from normal mice, whereas stimulation of ion transport by carbachol (10 microM) evoked an increase in short-circuit current that was similar in the two groups. Alterations in intestinal mass, morphology, or Na+, K+-ATPase activity could not account for the increase in absorptive function characteristic of piebald mice.

3-O-Methylglucose↗

PubMed1989

Correlation of structure and function in developing proximal tubule of guinea pig.

Unlike the case in rat, rabbit, and other species in which nephron formation continues into the newborn period, nephrogenesis in the guinea pig is completed well before the time of birth. Therefore, the marked increase in proximal tubule reabsorption that occurs during the postnatal period in that species can be attributed entirely to an increase in the absorptive capacity of existing nephron units. The purpose of the present morphometric studies was to correlate that change in proximal tubule function with changes in the apical and basolateral cell membrane surface areas. The apical and basolateral membrane surface densities were found to be approximately equal to each other and to remain constant throughout development. Because of increasing tubule volume, however, both membranes doubled in size between 1 and 3 wk of age and eventually increased by a factor of 3.5 in the adult. At the same time, there was little change in the length of tight function complexes measured in the plane of the luminal surface. Using previously published functional data and tubule length data, a good correlation was found between absolute absorption and total basolateral membrane surface area throughout the entire period of development in proximal tubules. Absorption per unit area of basolateral membrane was approximately 0.55, 0.41, 0.56, and 0.42 X 10(-6) nl.min-1.micron-2 in the 1st, 2nd, and 3rd wk, and in adult animals, respectively, and thus was similar to that reported for proximal tubule segments of adult rabbit and juvenile to adult rat.

Absorption↗

PubMed1988

Relationship between structure and function in renal proximal tubule.

Epithelia which support large transepithelial fluid movements are generally found to have histologic specializations which increase the surface areas of the cell membranes across which flows occur. A relationship between structure and function seems obvious in those cases. On the other hand, the area increasing specializations may also result in complicated shapes for the cells and their adjacent intercellular channels. In this paper we review the means for examining cell shape by quantitative stereologic techniques and the results obtained for the epithelium of the proximal renal tubule. We conclude that cell shape not only is a critical ingredient in any structure-function correlation for that tissue but also a "fingerprint" and a powerful tool with which one can predict and study epithelial absorptive flows and their driving forces.

Animals↗

PubMed1988

Structural and functional development of outer versus inner cortical proximal tubules.

The concept of centrifugal renal development is based on renal embryogenesis. It implies a relationship between nephron age and nephron position along a cortical to medullary axis. In common usage, however, it often also implies a relationship between nephron age or position and nephron maturity. We consider here whether the ideas of centrifugal development and centrifugal maturation should in fact be considered as separate and distinct concepts. That is, we consider the possibility that nephron maturity does not necessarily correlate with nephron age. Unfortunately, pertinent reported data give no clear answer. We conclude only that further study will be required before definitive conclusions about renal developmental stages can be stated with certainty.

Animals↗

PubMed1988

Model of renal cell volume regulation without active transport: role of a heteroporous membrane.

Isolated proximal renal tubules of rabbit reach a passive steady-state volume in isotonic medium after active transport is inhibited by ouabain or by inhibition of cellular metabolism or lack of metabolic substrates. If the tubules are then placed in a hypotonic NaCl medium they swell rapidly and then exhibit a volume regulatory decrease (VRD) similar to that seen when active transport is present. We have mathematically modeled these transient events by assuming that the basolateral cell membrane is permeated by pores having at least two distinct reflection coefficients with respect to sodium, potassium, and chloride. VRD depends on the difference of the values of the reflection coefficients of the pore types. As hydrostatic pressure is exerted by the stretching basement membrane, water and ions can be expelled from the cells across the lower reflection coefficient pores and cause VRD. When the hydrostatic pressure compliance is removed, the cells fail to volume decrease unless sufficient extracellular impermeant solute is present to provide an osmotic force for water and ion exit. We conclude that a heteroporous membrane may be an essential feature for cell volume regulation and maintenance.

Animals↗

PubMed1988

Theoretical models of cyst formation and growth.

Although the formation of fluid-filled, epithelial-lined cysts is a common event in a variety of tissues, the mechanisms involved are not well understood. Discussed here are means by which those mechanisms might be elucidated. In general, there are too few data available for complete analysis of in vivo disease processes. It can be suggested only that epithelial proliferation and basement membrane growth are probably absolute requirements. Whether the forces for fluid accumulation precede or follow the stimuli for cell growth cannot be stated with certainty. On the other hand, in certain in vitro model systems the forces required to keep cyst cavities filled with fluid may be so small that cell growth, rather than fluid accumulation, seems the more likely primary event.

Animals↗

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↗