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At least 1,153 records · Page 64Linked to original sources
PubMed1974

Osmotic extraction of hypotonic fluid from the lungs.

After injections of sucrose, NaCl, and urea solutions, the flow of tissue fluid from the lungs amounted to 0.182, 0.216, and 0.152 x 10(-3) ml/s per mosmol/kg of concentration difference between plasma and tissues in each gram of wet tissue weight. The extracted fluid contained less than 20% of the Na(+), K(+) and urea concentrations of the plasma. It was concluded that this fluid was distinctly hypotonic in comparision with the fluids of the plasma and tissue compartments both before and after the injection of hypertonic solutions. The presence of low solute concentrations in the extracted fluid is attributed to the passage of this fluid across cellular membranes, which are relatively impermeable to small hydrophilic solutes. Movement of fluid out of the junctions appears to be less than that through the endothelial cells. It is suggested that the injected solutes rapidly leak into the junctions and consequently induce relatively little movement of water or tissue solutes out of the junctions. Concentrations of tritiated water and [(14)C]antipyrine in the extracted fluid are essentially the same as base-line plasma concentrations when the animals have been primed with these tracers. It is therefore likely that these tracers can readily traverse cellular membranes. Red cell transit through the lungs is impaired by hypertonic solutions of sucrose and NaCl with transient increases in pulmonary arterial hemoglobin concentrations of as much as 35% of base-line values.

Animals↗
PubMed1986

Transepithelial water flow regulates apical membrane retrieval in antidiuretic hormone-stimulated toad urinary bladder.

Antidiuretic hormone (ADH) increases the osmotic water permeability (Posm) of toad urinary bladder. This increase is believed to be produced by fusion of intracellular vesicles called aggrephores with the granular cell apical plasma membrane. Aggrephores contain intramembrane particle aggregates postulated to be water channels. ADH-stimulated Posm is decreased by osmotic gradient exposure, which is termed flux inhibition. We studied flux inhibition by exposing ADH-stimulated bladders to various osmotic gradients. Osmotic water flow was initially proportional to the applied osmotic gradient, but Posm decreased with time. Ultrastructural and quantitative studies of endocytosis demonstrate that apical membrane retrieval was a direct function of the transepithelial osmotic gradient. Posm remained unchanged when apical membrane retrieval was blocked by incubation of bladders at 2 degrees C, or under low water-flow conditions. These effects were reversed by increases in temperature or the applied osmotic gradient. We conclude that apical membrane retrieval causes the phenomenon of flux inhibition.

Animals↗
PubMed2003

[Vasopressin-dependent water permeability of the basolateral membrane of the kidney outer medullary collecting duct in postnatal ontogenesis in rats].

Kidneys of new-born animals are resistant to arginine vasopressin (AVP). The ability of the hormone to regulate water permeability of the collecting duct can be seen from weaning period, probably due to the maturation of the intracellular signaling pathway. The purpose of the present work was to investigate the effect of V2 receptor agonist dDAVP on the water permeability of OMCD basolateral membrane in 10-, 22- and 60-day old Wistar rats. We also estimated ontogenetic gene expression of AQP2, AQP3, AQP4 and V2 receptor. Osmotic water permeability (Pf) of the basolateral membrane of microdissected OMCD was measured under control conditions and after incubation with the agonist V2 receptor desmopressin (dDAVP; 10(-7) M). Water permeability in 10- and 22-day old rats under control conditions were significantly higher than in adults. Desmopressin stimulated significant increase of this parameter in 22-day old pups (Pf = = 125 +/- 4.85; Pf = 174 +/- 8.2 microns/s, p < 0.001) and adult rats (Pf = 100.5 +/- 7.38; Pf = 178.8 +/- 9.54 microns/s, p < 0.001). Osmotic water permeability of the OMCD basolateral membrane in 10-day old rats does not depend on dDAVP (Pf = 172.5 +/- 23.8; Pf = 164.8 +/- 34 microns/s). With the RT-PCR, we observed a gradual increase of AQP2 and V2 receptor genes expression during postnatal ontogenesis. The gene expression of AQP3 and AQP4 remained unchanged during postnatal ontogenesis. In general, the water permeability of the OMCD basolateral membrane of rats can be stimulated by AVP since the 22nd day of postnatal life. The water permeability of the OMCD basolateral membrane under control conditions gradually decreased during postnatal development, while gene expression of AQP3 and AQP4 was unchanged. The mechanism of this decrease remains to be established.

Aging↗
PubMed1990

Reversible inactivation of water and sodium transport systems in frog urinary bladder and skin in the presence of detergents.

Detergents (Triton X-100, dodecyl sulphate, saponin) added in concentrations of 0.1-10 mg/ml to solution at the outer frog skin surface reversibly reduced potential difference (PD) and short-circuit current (Isc); when added at the inner surface. Triton X-100 initially induced a short increase in the PD and Isc followed by a pronounced decrease similarly as after the application of any of the detergents used. When added to either serosal or mucosal surface of frog urinary bladder, the detergents reversibly abolished the reactivity to vasopressin. Triton X-100 blocked foskolin and cAMP-induced effects on membrane water permeability. The results suggest that hydrophobic elements of membrane play a crucial role in the regulation of membrane permeability for ions and water and of the responsiveness of the cells to vasopressin. Differences in sensitivity to detergents could be observed between the apical and the basolateral cell membrane.

Animals↗
PubMed2004

Removal of endocrine disrupting compounds with membrane processes in wastewater treatment and reuse.

Endocrine disrupting compounds can affect the hormone system in organisms and are the subject of environmental and human health concerns. The effluents of wastewater treatment plants contribute to the emission of estrogenically active substances into the environment. Membrane technology, which is an advanced wastewater treatment option, is the subject of this research. The removal techniques under investigation are membrane bioreactors, reverse osmosis, and nanofiltration. Eleven different nanofiltration membranes were tested in the laboratory set-up. The observed retention of NP and BPA ranged between 70% and 100%. The contact angle is an indicator for the hydrophobicity of a membrane, whose influence on the permeability and retention of NP was evident. Regarding the retention of BPA no dependency on the contact angle was observed. Results of the investigation of a full-scale landfill leachate treatment plant indicate a bisphenol A (BPA) removal of more than 98% with membrane bioreactors and reverse osmosis. The mass balance indicates that biological degradation is the most important removal process in the membrane bioreactor configuration.

Benzhydryl Compounds↗
PubMed1977

Permeability of the cell envelope and osmotic behavior in Saccharomyces cerevisiae.

Bakers' yeast (Saccharomyces cerevisiae) was equilibrated with distilled water and then packed into standardized pellets by centrifugation. The fractional space (S value) that was accessible to passive permeation was probed with a variety of mono- and divalent salts, mono- and disaccharides, polyols, substrates and products of beta-fructofuranosidase (EC 3.2.1.26) and acid phosphatase (EC 3.1.3.2), and a cross-linked polymer of sucrose (Ficoll 400). A simple but very reproducible method was developed to measure pellet volume. At the limit of zero osmolality for bathing medium, the interstitial space was 0.223 ml/ml of pellet, and the aqueous volume of cell envelopes was 0.117 ml/ml of pellet. Thus the cell envelope for this yeast, under these conditions, was approximately 15% of the total cell volume. At a finite osmolality, the space in a yeast pellet that was accessible to salt was accounted for by the sum of initial interstitial space, the volume of the cell envelopes, and the volume of water abstracted from the cells by osmosis. Plots of S value versus osmolality were linear for uncharged probes and curvilinear for all salts. When Ficoll and potassium thiocyanate were presented to the yeast in admixture, the S values for the salt increased continuously over the range of osmolality studied. However, the S values for Ficoll 400 (which did not penetrate the cell wall) were lower by an amount equilivalent to the cell envelopes; they increased in parallel with the S curve for salt up to 1.15 osmol/kg and then plateaued. The results support the concept of incipient plasmolysis at 1.15 osmol/kg, and the separation of protoplasm from the cell wall is indicated with more concentrated solutions. Such cells were still viable if slowly diluted in distilled water, but they were injured by the shock of rapid dilution. However, shocking the cells did not release beta-fructofuranosidase into the medium. The complete accessibility of salts toward killed cells was demonstrated with yeast that had been pretreated with heat, organic solvents, or glutaraldehyde.

Acid Phosphatase↗
PubMed2006

Water transport by GLUT2 expressed in Xenopus laevis oocytes.

The glucose transporter GLUT2 has been shown to also transport water. In the present paper we investigated the relation between sugar and water transport in human GLUT2 expressed in Xenopus oocytes. Sugar transport was determined from uptakes of non-metabolizable glucose analogues, primarily 3-O-methyl-D-glucopyranoside; key experimental results were confirmed using D(+)-glucose. Water transport was derived from changes in oocyte volume monitored at a high resolution (20 pl, 1 s). Expression of GLUT2 induced a sugar permeability, P(S), of about 5 x 10(-6) cm s(-1) and a passive water permeability, L(p), of 5.5 x 10(-5) cm s(-1). Accordingly, the passive water permeability of a GLUT2 protein is about 10 times higher than its sugar permeability. Both permeabilities were abolished by phloretin. Isosmotic addition of sugar to the bathing solution (replacing mannitol) induced two parallel components of water influx in GLUT2, one by osmosis and one by cotransport. The osmotic driving force arose from sugar accumulation at the intracellular side of the membrane and was given by an intracellular diffusion coefficient for sugar of 10(-6) cm(2) s(-1), one-fifth of the free solution value. The diffusion coefficient was determined in oocytes coexpressing GLUT2 and the water channel AQP1 where water transport was predominantly osmotic. By the cotransport mechanism about 35 water molecules were transported for each sugar molecule by a mechanism within the GLUT2. These water molecules could be transported uphill, against an osmotic gradient, energized by the flux of sugar. This capacity for cotransport is 10 times smaller than that of the Na(+)-coupled glucose transporters (SGLT1). The physiological role of GLUT2 for intestinal transport under conditions of high luminal sugar concentrations is discussed.

Animals↗
PubMed1998

Urea transporter UT3 functions as an efficient water channel. Direct evidence for a common water/urea pathway.

A family of molecular urea transporters (UTs) has been identified whose members appear to have an exceptionally high transport turnover rate. To test the hypothesis that urea transport involves passage through an aqueous channel, osmotic water permeability was measured in Xenopus oocytes expressing UTs. The UT3 class of urea transporters functioned as efficient water channels. Quantitative measurement of single channel water permeability (pf) using epitope-tagged rat UTs gave pf (in cm3/s x 10(-14)) of 0.14 +/- 0.11 (UT2) and 1.4 +/- 0.2 (UT3), compared with 6.0 and 2.3 for water channels AQP1 and AQP3, respectively. Relative single channel urea permeabilities (purea) were 1.0 (UT2), 0.44 (UT3), and 0.0 (AQP1). UT3-mediated water and urea transport were weakly temperature-dependent (activation energy <4 kcal/mol), inhibited > 75% by the urea transport inhibitor 1,3-dimethylthiourea, but not inhibited by the water transport inhibitor HgCl2. To test for a common water/urea pore, the urea reflection coefficient (sigmaurea) was measured by independent induced osmosis and solvent drag methods. In UT3-expressing oocytes, the time course of oocyte volume in response to different urea gradients (induced osmosis) gave sigmaurea approximately 0.3 for the UT3 pathway, in agreement with sigmaurea determined by the increase in uptake of [14C]urea during osmotic gradient-induced oocyte swelling (solvent drag). In oocytes of comparable water and urea permeability coexpressing AQP1 (permeable to water, not urea) and UT2 (permeable to urea, not water), sigmaurea = 1. These results indicate that UT3 functions as a urea/water channel utilizing a common aqueous pathway. The water transporting function and low urea reflection coefficient of UT3 in vasa recta may be important for the formation of a concentrated urine by countercurrent exchange in the kidney.

Animals↗
PubMed2003

Quantitative analysis of hyperosmotic and hypothermic blood-brain barrier opening.

Hyperosmotic opening of the blood-brain barrier (BBB) by mannitol is being used to enhance drug transport in human brains. Recently, cooling of the solution has been reported to have potential to open the BBB. However, the mechanism in barrier opening and closure remains elusive. We studied the rapid changes in cerebrovascular permeability after hyperosmotic and hypothermic BBB opening in rats, and then demonstrated that the Na+/Ca++ exchange blocker (KB-R7943) prolongs opening. BBB opening was attained by using intra-arterial infusion of hyperosmotic mannitol (1.6 M) and 1.1 M mannitol (which is less hyperosmotic than commonly used mannitol) at 4 degrees in Sprague-Dawley (SD) rats. To measure the changes in cerebrovascular permeability, perfusate-containing [14C]-sucrose was infused intra-arterially at different time points following hyperosmotic and hypothermic stress. Cerebrovascular permeability was then measured with the in situ brain perfusion technique. 1.6 M Mannitol produced opening of the BBB but the duration of the opening was less than 30 minutes. Use of 1.1 M Mannitol at 4 degrees indicated the same results. We then investigated the effect of a Na/Ca ion exchange blocker (KB-R7943) in both hyperosmotic and hypothermic BBB opening. KB-R7943 extended BBB opening up to 30 min without affecting the peak level of BBB permeability at 5 minutes. Our findings represent important experimental information regarding pharmacological manipulation of BBB opening. The possibility of prolonging the transient opening of the BBB has major clinical implications.

Animals↗
PubMed1988

Modulation of water transport in human red cells: effect of urea.

We have studied the effect of urea on water flux in the human red cell and have found that 500 mosmolal urea inhibits osmotic water transport by 39%. The Ki for urea inhibition of water flux is 550 +/- 80 mosmolal, higher than, but comparable with, the Km of urea transport into the red cell of 220-330 mM given by Mayrand and Levitt (J. Gen. Physiol. 55 (1983) 427) and Brahm (J. Gen. Physiol. 82 (1983) 1). Other amides, such as propionamide and valeramide, as well as methyl-substituted ureas, have similar effects, although an indifferent molecule, such as 0.5 M creatinine, has no effect. Urea can be washed off the inhibition site with buffer, and the effects of urea concentrations as high as 1.2 osmolal are entirely reversible. 500 mosmolal urea also significantly increases the reflection coefficient for ethylene glycol, sigma eth gly, from 0.71 +/- 0.03 in control experiments to 0.86 +/- 0.04 (P less than 0.0005, t-test), and propionamide has a similar effect on sigma eth gly. These results show that urea can modulate ethylene glycol transport through the red cell membrane, and are consistent with, but not proof of, the presence of a single class of aqueous channels through which both ethylene glycol and urea enter the red cell. It is suggested that the physiological purpose of these low-affinity urea sites is to modulate water flow out of the red cell during passage through the regions of 0.5-0.6 M urea in the kidney.

Amides↗