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PubMed1984

Epithelial cell volume regulation in hypotonic fluids: studies using a model tissue culture renal epithelial cell system.

The cultured renal epithelial cell line MDCK has been used in a study of cell volume regulation, emphasis being placed upon cell swelling in hypotonic media. MDCK cell volume was measured directly by electronic cell sizing using a Coulter counter in MDCK cell suspensions; this method gave comparable values for cell water when compared with those obtained using an intracellular space marker [14C]3-O-methyl glucose. MDCK cells behaved as perfect osmometers when suspended in hypertonic fluid (cell shrinkage). Cellular swelling in hypotonic media, in certain conditions, was found to be less than expected for an ideal osmometer. Non-ideal swelling was found to be the result of a substantial loss of intracellular K+ (Cl-) due to a specific increase in membrane K+ permeability. The membrane channel mediating the increased net K+ loss was separate, by pharmacological identity, from the Na+-K+ pump, the diuretic-sensitive co-transport system and a Gardos-type channel inhibited by quinine. A role for increased Ca2+ influx mediating the increased K+ permeability is suggested by results from hypotonic exposure in nominally Ca2+-free solutions.

Animals↗
PubMed1975

The stages of osmotic haemolysis.

The haemolysis of individual human erythrocytes has been observed using an inverted microscope and cine-camera. 2. With each permeant (glycerol, propylene glycol, ethylene glycol, urea and water) haemolysis is a multistage process. The stages are swelling, popping, reduction in volume possibly accompanied by ion leakage and, finally, haemoglobin leakage. 3. The classical haemolysis time (Th) is made up of a swelling time (Tsw) and a stress time (Tst). Tst is not negligible and with the faster permeants it may occupy more than 75% of the haemolysis time. 4. The stress time can also be divided into two parts: a K+ leak time (TK) during which the cell shrinks and a time (THb) during which haemoglobin is leaving the cell. THb occupies a substantial part of Th, from 25 to 65%, and is relatively longer in fast haemolysis. 5. There is a wide spread in the permeability coefficient to glycerol in a population of erythrocytes. The distribution is compatible with a Gaussian distribution. The mean permeability is 1-79 X 10(-6) cm/sec and the S.D. is +/0 0-45 X 10(-6) cm/sec. 6. The correlation between haemolysis time and swelling time for individual erythrocytes is poor, especially for fast haemolysis. Consequently, a measure of the distribution of haemolysis time does not give a related distribution of the swelling time or of the calculated permeability for individual erythrocytes.

Cell Membrane Permeability↗
PubMed1987

Absence of significant cellular dilution during ADH-stimulated water reabsorption.

Water reabsorption across many "tight" urinary epithelia is driven by large transepithelial osmotic gradients and is controlled by antidiuretic hormone (ADH). Numerous investigators have concluded that ADH-induced water reabsorption causes large apparent increases in cell volume with concomitant cytoplasmic dilution. A central question in renal physiology has been how cellular homeostasis is maintained in tight urinary epithelia during antidiuresis. Previous direct measurements of cell membrane permeability to water and the present direct measurements of cell volume in collecting tubules of rabbit kidney cortex by quantitative light microscopy show that cell volume does not change significantly during transcellular water flow. Fluid transported across the epithelium accumulated in lateral and basal intercellular spaces; the effect was an increase in cell height and tubule wall thickness accompanied by maintenance of nearly constant cell volume. The stability of cell volume is a consequence of the relatively high water permeability of the blood-facing cell membrane.

Absorption↗
PubMed1984

Responses of lymphocytes to anisotonic media: volume-regulating behavior.

The regulatory responses elicited in lymphoid cells suspended in anisotonic media are reviewed. The immediate response approximates osmometric behavior. In addition, in hypotonic media, the initial osmometric swelling is followed by a regulatory volume decrease (RVD), which is associated with KCl loss. The volume-induced effluxes of K+ and Cl- are mediated by two independent conductive pathways. Ca2+-depletion experiments and studies of inhibitor susceptibility suggest that Ca2+ may mediate the activation of the K+ pathway. The responses of the two main lymphocyte subpopulations to hypotonic challenge are different. RVD is much more rapid in T- than in B-cells, regardless of their tissue of origin. Under certain conditions, shrunken lymphocytes will regain their initial volume. This regulatory volume increase (RVI) is due to NaCl uptake, followed by a secondary exchange of Na+ for K+ via the Na+-K+ pump. Na+ is primarily taken up in exchange for H+ through an amiloride-sensitive pathway, whereas Cl- enters in exchange for HCO-3 (or OH-). Anion and cation fluxes responsible for RVI are electroneutral. Some of the volume-sensitive pathways can also be activated in isotonic cells. The conductive K+ pathway is activated by Ca2+ plus ionophore A23187, and the Na+-H+ exchanger can be activated by cytoplasmic acidification. The responses of lymphocytes to anisotonic challenge are compared with those of other cells, and the possible significance of the volume-induced fluxes is discussed.

Animals↗
PubMed1990

Microvascular permeability to endogenous plasma proteins in the jejunum.

Steady-state lymph flow and lymph (CL) and plasma (CP) protein concentrations were measured at venous outflow pressures of 0, 10, 20, and 30 mmHg in an autoperfused segment of cat jejunum. In addition to determining total protein concentrations in lymph and plasma, polyacrylamide gradient gel electrophoresis was used to determine lymph and plasma protein concentrations of albumin and nine other plasma proteins. The osmotic reflection coefficient (sigma d) for total proteins, albumin, and each of the nine protein fractions was estimated using CL/CP at a capillary filtration rate independent state, when 1 - CL/CP = sigma d. A sigma d of 0.83 was obtained for total proteins, a value similar to that reported for both dog jejunum and descending colon (0.85) but appreciably different from that reported for both cat stomach (0.78) and ileum (0.92). Additionally, sigma d for albumin and each of the nine plasma protein fractions (molecular radii ranging from 37 to 120 A) increased as molecular radius increased. A two-pore model composed of a ratio of 3,750 48-A radius small pores to one 250-A radius large pore describes the data obtained, with 82% of the total volume flow occurring through the small pores and 16% through the large pores.

Animals↗
PubMed2005

The transport barrier in intraperitoneal therapy.

The peritoneal cavity is important in clinical medicine because of its use as a portal of entry for drugs utilized in regional chemotherapy and as a means of dialysis for anephric patients. The barrier between the therapeutic solution in the cavity and the plasma does not correspond to the classic semipermeable membrane but instead is a complex structure of cells, extracellular matrix, and blood microvessels in the surrounding tissue. New research on the nature of the capillary barrier and on the orderly array of extracellular matrix molecules has provided insights into the physiological basis of osmosis and the alterations in transport that result from infusion of large volumes of fluid. The anatomic peritoneum is highly permeable to water, small solutes, and proteins and therefore is not a physical barrier. However, the cells of the mesothelium play an essential role in the immune response in the cavity and produce cytokines and chemokines in response to contact with noncompatible solutions. The process of inflammation, which depends on the interaction of mesothelial, interstitial, and endothelial cells, ultimately leads to angiogenesis and fibrosis and the functional alteration of the barrier. New animal models, such as the transgenic mouse, will accelerate the discovery of methods to preserve the functional peritoneal barrier.

Animals↗
PubMed1990

Water permeability of apical and basolateral cell membranes of rat inner medullary collecting duct.

To quantify the pathways for water permeation through the kidney medulla, knowledge of the water permeability (Posmol) of individual cell membranes in inner medullary collecting duct (IMCD) is required. Therefore IMCD segments from the inner two thirds of inner medulla of Sprague-Dawley rats were perfused in vitro using a setup devised for rapid bath and luminal fluid exchanges (half time, t1/2, of 55 and 41 ms). Differential interference contrast microscopy, coupled to video recording, was used to measure volume and approximate surface areas of single cells. Volume and volume-to-surface area ratio of IMCD cells were strongly correlated with their position along the inner medullary axis. Transmembrane water flow (Jv) was measured in response to a variety of osmotic gradients (delta II) presented on either basolateral or luminal side of the cells. The linear relation between Jv and delta II yielded the cell membrane Posmol, which was then corrected for membrane infoldings. Basolateral membrane Posmol was 126 +/- 3 microns/s. Apical membrane Posmol rose from a basal value of 26 +/- 3 microns/s to 99 +/- 5 microns/s in presence of antidiuretic hormone (ADH). Because of amplification of basolateral membrane, the ADH-stimulated apical membrane remained rate-limiting for transcellular osmotic water flow, and the IMCD cell did not swell significantly. Calculated transcellular Posmol, expressed in terms of smooth luminal surface, was 64 microns/s without ADH and 207 microns/s with ADH. IMCD cells in anisosmotic media displayed almost complete volume regulatory decrease but only partial volume regulatory increase.

Animals↗
PubMed1973

Effect of phloretin on water and solute movement in the toad bladder.

It is generally believed that urea crosses the cell membrane through aqueous channels, and that its movement across the membrane is accelerated in the direction of net water flow (solvent drag effect). The present report presents evidence for a vasopressin-sensitive pathway for the movement of urea, other amides, and certain non-amides, which is independent of water flow. Phloretin, when present at 10(-4) M concentration in the medium bathing the luminal surface of the toad bladder, strongly inhibits the movement of urea, acetamide, and propionamide across the toad bladder, both in the absence and presence of vasopressin. The vasopressin-stimulated movement of formaldehyde and thiourea is also reduced. Osmotic water flow, on the other hand, is not affected; nor is the movement of ethanol and ethylene glycol, or the net transport of sodium. On the basis of these studies we would conclude that the movement of many, if not all, solutes across the cell membrane is independent of water flow, and that a vasopressin-sensitive carrier may be involved in the transport of certain solutes across the cell membrane.

Acetamides↗
PubMed1990

Ultrastructural localization of blood-retinal barrier breakdown in diabetic and galactosemic rats.

Breakdown of the blood-retinal barrier (BRB) is an early event in diabetic and galactosemic rats, but the location and nature of the specific defect(s) are controversial. Using an electron microscopic immunocytochemical technique, the retinas of normal, diabetic, and galactosemic rats were immunostained for endogenous albumin. Normal rats showed little evidence of BRB breakdown at either the inner barrier (retinal vasculature) or the outer barrier (retinal pigment epithelium) (RPE). In diabetic and galactosemic rats, as was true in human diabetics, BRB breakdown occurred predominantly at the inner BRB, but in some cases at the outer barrier as well. Treatment with the aldose reductase inhibitor sorbinil largely prevented BRB failure in galactosemic rats. In the inner retina of diabetic and galactosemic rats, albumin was frequently demonstrated on the abluminal side of the retinal capillary endothelium (RCE) in intercellular spaces, basal laminae, pericytes, ganglion cells, astrocytes, and the perinuclear cytoplasm of cells in the inner nuclear layer. Albumin did not appear to cross RCE cell junctions; however, it was occasionally seen in RCE cytoplasm of galactosemic rats. In the outer retina, albumin was frequently detected in the subretinal space, in the intercellular space between photoreceptors, and in the perinuclear cytoplasm of photoreceptor cells, but was only infrequently found in the RPE cells constituting the barrier. Albumin derived from the choroidal vasculature did not appear to cross the tight junctions of the RPE. These findings suggest that specific sites of BRB compromise are infrequent but that once albumin has crossed the RCE or RPE it freely permeates the retinal tissue by filling intercellular spaces and permeating the membranes of cells not implicated in BRB formation. The diffuse cytoplasmic staining of some RCE and RPE cells suggests that the predominant means of BRB breakdown in diabetes and galactosemia involves increased focal permeability of the surface membranes of the RCE and RPE cells rather than defective tight junctions or vesicular transport.

Albumins↗
PubMed2000

Molecular identification of functional water channel protein in cultured human nonpigmented ciliary epithelial cells.

PURPOSE: Water channel proteins are important pathways for water movements across cell membranes, including those in the ciliary epithelium, which is the major site of aqueous humor secretion. In this study, we aimed to demonstrate the expression of functionally active aquaporin-1 (AQP1) water channels in cultured human ciliary epithelial cells. METHODS: Poly A(+) RNA was isolated from cell cultures of Simian Virus 40 (SV-40) transformed human nonpigmented ciliary epithelium (NPE) subjected to RT-PCR reaction using primers specific to AQP1. Northern analysis was used to define the expression of AQP1 in NPE cells. Western immunoblotting with polyclonal antibody raised against AQP1 was used to evaluate the AQP1 protein expression in the plasma membranes of human NPE cells. Light scattering method was used to determine the osmotic water permeability in the suspension of NPE cells. RESULTS: RT-PCR using specific primers for AQP1, Northern analysis and Western immunoblot using AQP1 specific antibody demonstrated the expression of AQP1 in the plasma membranes of NPE cells. Osmotic water permeability (P( f)) measurements confirmed that functional AQP1 water channels are expressed in human NPE cells and the P(f) for these cells was 9.8 x 10( -3) cm/s at 10 degrees C. CONCLUSIONS: The presence of AQP1 in human NPE cells suggests that it may have a role in the fluid flow across epithelial membranes. In addition, the existence of AQP1 in the human NPE cells provide an excellent in vivo model to study the regulation of aquaporins and their possible role in the aqueous humor secretion.

Animals↗
PubMedDate not supplied

Kinetics of osmotic water movement from rabbit patellar tendon and medial collateral ligament fibroblasts.

The present study is part of a program to optimize the cryopreservation ligament and tendon allografts for the biological remodeling that occurs following transplantation. The osmotic behavior of fibroblasts from the medial collateral ligament (MCL) and the patellar tendon (PT) of new zealand white rabbits was measured to obtain the hydraulic conductivity (and its temperature dependence) as well as the osmotically inactive volume. MCL fibroblasts were found to have an isotonic cell volume of 3800 (m(3), an osmotically inactive volume of 1300 (microm(3), and a hydraulic conductivity of 0.56 (microm/min/atm at 20 degrees C with an activation energy of 10.9 kcal/mol. PT fibroblasts were found to have an isotonic cell volume of 6300 (microm(3), an osmotically inactive volume of 2000 (microm(3), and a hydraulic conductivity of 0.71 (m/min/atm at 20 degrees C with an activation energy of 10.1 kcal/mol.

Animals↗
PubMed1991

Functional unit of 30 kDa for proximal tubule water channels as revealed by radiation inactivation.

The high water permeability of kidney proximal tubules is of paramount importance for isotonic reabsorption of 70% of the glomerular filtrate, and water channels have been postulated to account for the high water permeability. Target analysis following radiation inactivation was used to probe the molecular size of the water channel. Samples of brush border membranes from rat renal cortex were subjected to 3-MeV electron pulses from the Van de Graaff accelerator at a temperature of -130 degrees C. The inactivation of the renal brush border enzymes, alkaline phosphatase, and maltase was used for internal standardization of accumulated dose measurements in target analysis of the water channel. Osmotic water permeability was measured by following the change in scattered light intensity upon rapid mixing of vesicles with a hypertonic solution using stopped-flow spectrophotometry. The vesicle shrinkage response was biphasic and the rate of the fast phase decreased dose dependently by irradiation corresponding to a target size of 30 +/- 3.5 kDa. The total change in scattered light intensity was unaltered, indicating that irradiation did not destroy the lipid barrier. Our results provide strong support for the hypothesis that the high osmotic water permeability of renal proximal tubules results from a water channel-specific protein with a functional unit of 30 kDa.

Alkaline Phosphatase↗