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PubMedDate not supplied

Chondrocyte hypertrophy in the growth plate: a short communication on probable mechanism.

The process by which chondrocytes hypertrophy has been deduced from observations on standard histology sections of the rabbit growth plate is reported. Features suggestive of an osmotic process were observed, namely a hierarchy of cell sizes, cell rupture, an adjoining 'open' microcirculation and a permeable partition between cells and blood.

Animals↗
PubMed2006

[Calciumdependent mechanisms in vasopressin regulation of osmotic water permeability in the mouse kidney collecting duct cells].

In the study, the role of PKC and Ca++ in vasopressin regulation of the plasma membrane water permeability was studied in the cells of the mouse kidney collecting duct. Coefficient of osmotic water permeability of total cell surface (Pf) was calculated from the initial rate of cell swelling following the osmotic shock caused by changing the medium osmolarity from isotonic to hypotonic (300 mOsm to 200 mOsm). Desmopressin (dDAVP 1 nM) increased the Pf in hydrated mice from 168.4 +/- 11.8 microm/s up to 231.3 +/- 14.7 microm/s. The Ca++ chelator BAPTA prevented the desmopressin-induced increase in water permeability. Inhibition of PKC (Ro-31-8220 0.1 microM) also abolished the desmopressin-stimulated increase of plasma membrane water permeability, whereas inhibitor of PKC alone did not suppress the stimulation of the water permeability by db-cAMP. The PKC activity and calciumdependent second messengers seem to be important for regulation of water permeability by vasopressin.

Animals↗
PubMedDate not supplied

[Comparative study of the role of cAMP, cGMP and Ca2+ in the action of the antidiuretic hormone on bladder cells of the frog].

Vasopressin (ADH), forskolin and cAMP raise osmotic pressure of the frog bladder; cGMP does not change the response of cells to cAMP and forskolin action but it increases the ADH effect. Being added from the mucous or serous membranes, Ca channel blocker (fendiline) and calmodulin antagonist (thioridazine) inhibit the water effect of ADH. The results obtained indicate a number of loci where Ca2+ is in ADH-dependent reactions which cause an increase in osmotic permeability.

Animals↗
PubMed2005

Asymmetry in the osmotic response of a rat cortical collecting duct cell line: role of aquaporin-2.

Transition from antidiuresis to diuresis exposes cortical collecting duct cells (CCD) to asymmetrical changes in environment osmolality, inducing an osmotic stress, which activates numerous membrane-associated events. The aim of the present work was to investigate, either in the presence or not of AQP2, the transepithelial osmotic water permeability (P(osm)) following cell exposure to asymmetrical hyper- or hypotonic gradients. For this purpose, transepithelial net volume fluxes were recorded every minute in two CCD cell lines: one not expressing AQPs (WT-RCCD(1)) and another stably transfected with AQP2 (AQP2-RCCD(1)). Our results demonstrated that the rate of osmosis produced by a given hypotonic shock depends on the gradient direction (osmotic rectification) only in the presence of apical AQP2. In contrast, hypertonic shocks elicit P(osm) rectification independently of AQP2 expression, and this phenomenon may be linked to modulation of basolateral membrane permeability. No asymmetry in transepithelial resistance was observed under hypo- or hypertonicity, indicating that rectification cannot be attributed to a shunt through the tight junction path. We conclude that osmotic rectification may be explained in terms of dynamical changes in membrane permeability probably due to activation/incorporation of AQPs or transporters to the plasma membrane via some mechanism triggered by osmolality.

Animals↗
PubMed1996

Permeability of intact and dechorionated eggs of the Anopheles mosquito to water vapor and liquid water: a comparison with Drosophila.

As an initial step in the development of cryopreservation methods for Anopheles gambiae embryos, we determined the permeability of intact and dechorionated A. gambiae embryos to water and ethylene glycol and compared those permeabilities with those of Drosophila melanogaster embryos. Most studies were conducted on embryos allowed to develop for 8 h at 26 degrees C or 15 h at 17 degrees C. Intact A. gambiae embryos are some 50 times more permeable to water vapor than are D. melanogaster embryos; e.g., when air dried, half of 15 h/17 degrees C A. gambiae embryos become severely dehydrated in 3. 5-4.0 min, whereas comparably aged D. melanogaster embryos require approximately 4 h or more. Comparable differences between the two species exist with respect to the loss of liquid water under an osmotic driving force. After 90 min in 0.75 M sucrose in 0.26 osmolal D-20 Drosophila medium, 25-40% of intact A. gambiae embryos underwent extensive shrinkage, whereas D. melanogaster embryos showed no shrinkage. The chorion of both species can be removed by a 2.5-min exposure to 50% household bleach (Clorox). Dechorionation increases the rate of water loss two- to sixfold during air drying in both species and during exposure to hyperosmotic sucrose in A. gambiae. Dechorionated D. melanogaster embryos, however, show no shrinkage in hyperosmotic sucrose even after 6 h. The water permeability of dechorionated A. gambiae embryos thus remains many-fold higher than that of dechorionated D. melanogaster embryos. Although moderately permeable to water, neither intact nor dechorionated A. gambiae embryos are permeable to ethylene glycol, as evidenced by the failure of dehydrated embryos to reexpand in 120-180 min in that solution.

Animals↗
PubMed2002

Transmembrane water influx via aquaporin-1 is inhibited by barbiturates and propofol in red blood cells.

Aquaporin-1 (AQP1) is known to be expressed at a high level in endothelial cell membranes and participates in water transfer into or across these cells. To evaluate possible effects of anesthetics on AQP1, a model assessing water permeability of erythrocytes was used, AQP1 being the exclusive water channel in red blood cells (RBC). RBC were suspended in hypertonic (1.35%) or hypotonic (0.45%) phosphate-buffered saline (PBS). Optical density was measured continuously in an aggregometer before and during subsequent addition of hypotonic (0.45%) or hypertonic (9%) PBS, respectively. Rates of change of optical density corresponded to the rate of volume change due to osmotic effects on net water flux across the RBC membrane. We compared actions of mercuric chloride (HgCl(2), definitive AQP1-blocker, 0.2 microM), and different anesthetic drugs, such as thiopental (50-200 microg/ml), phenobarbital (30-220 microg/ml), propofol (15-25 microg/ml), ketamine (3.5-11 microg/ml), midazolam (0.2-32.5 microg/ml), halothane (1.5 vol%), and isoflurane (2.3 vol%); the concentrations being in the one- to threefold range of clinically relevant plasma levels. Water transport into RBC (swelling) was inhibited by HgCl(2), thiopental, phenobarbital and propofol while ketamine, midazolam, halothane, and isoflurane had no effect. Efflux of water (shrinking) was also inhibited by HgCl(2), confirming a significant role of AQP1 in this model. In contrast, none of the tested anesthetic substances had any influence on water efflux. Comparison to chemically related drugs suggested oxidation of a strategic SH-group to be the mode of action. The anesthetics thiopental, phenobarbital, and propofol significantly inhibited influx of water into RBC, while water efflux remained unaffected in distinction to HgCl(2). These anesthetics thus acted as vectorial inhibitors, a hitherto undescribed phenomenon. Accordingly, some anesthetics may indeed affect transport of water via aquaporins.

Anesthetics, Intravenous↗
PubMed1985

Target analysis studies of red cell water and urea transport.

Radiation inactivation was used to determine the nature and molecular weight of water and urea transporters in the human red cell. Red cells were frozen to -50 degrees C in a cryoprotectant solution, irradiated with 1.5 MeV electrons, thawed, washed and assayed for osmotic water and urea permeability by stopped-flow light scattering. The freezing and thawing process did not affect the rates of water or urea transport or the inhibitory potency of p-chloromercuribenzenesulfonate (pCMBS) on water transport and of phloretin on urea transport. Red cell urea transport inactivated with radiation (0-4 Mrad) with a single target size of 469 +/- 36 kDa. 40 microM phloretin inhibited urea flux by approx. 50% at each radiation dose, indicating that urea transporters surviving radiation were inhibitable. Water transport did not inactivate with radiation; however, the inhibitory potency of 2.5 mM pCMBS decreased from 86 +/- 1% to 4 +/- 9% over a 0-2 Mrad dose range. These studies suggest that red cell water transport either required one or more low-molecular-weight proteins, or is lipid-mediated, and that the pCMBS-binding site which regulates water flow inactivates with radiation. These results also suggest that red cell urea transport is mediated by a specific, high-molecular-weight protein. These results do not support the hypothesis that a band 3 dimer (190 kDa) mediates red cell osmotic water and urea transport.

4-Chloromercuribenzenesulfonate↗
PubMed1985

Binding of DTNB to band 3 in the human red cell membrane.

Inhibition of red cell water transport by the sulfhydryl reagent 5,5'-dithiobis(2-nitrobenzoic acid) (DTNB) has been reported by Naccache and Sha'afi ((1974) J. Cell Physiol. 84, 449-456) but other investigators have not been able to confirm this observation. Brown et al. ((1975) Nature 254, 523-525) have shown that, under appropriate conditions, DTNB binds only to band 3 in the red cell membrane. We have made a detailed investigation of DTNB binding to red cell membranes that had been treated with the sulfhydryl reagent N-ethylmaleimide (NEM), and our results confirm the observation of Brown et al. Since this covalent binding site does not react with either N-ethylmaleimide or the sulfhydryl reagent pCMBS (p-chloromercuribenzenesulfonate), its presence has not previously been reported. This covalent site does not inhibit water transport nor does it affect any transport process we have studied. There is an additional low-affinity (non-covalent) DTNB site that Reithmeier ((1983) Biochim. Biophys. Acta 732, 122-125) has shown to inhibit anion transport. In N-ethylmaleimide-treated red cells, we have found that this binding site inhibits water transport and that the inhibition can be partially reversed by the specific stilbene anion exchange transport inhibitor 4,4'-diisothiocyanostilbene-2,2'-disulfonate (DIDS), thus linking water transport to anion exchange. DTNB binding to this low-affinity site also inhibits ethylene glycol and methyl urea transport with the same KI as that for water inhibition, thus linking these transport systems to that for water and anions. These results support the view that band 3 is a principal constituent of the red cell aqueous channel, through which urea and ethylene glycol also enter the cell.

4-Chloromercuribenzenesulfonate↗