PubMed Health⌕ Search

SEARCH · PubMed Health

Results for “OSMOSIS AND PERMEABILITY”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 973 records · Page 54Linked to original sources
PubMed1994

Stretch sensitivity of transmembrane mobility of hydrogen peroxide through voids in the bilayer. Role of cardiolipin.

Availability of voids for diffusion of quinone in the membrane was shown to be the rate-limiting step in electron transport in mitochondria and chloroplasts (Mathai, J. C., Sauna, Z. E., John, O., and Sitaramam, V (1993) J. Biol. Chem. 268, 15442-15454). The primary role of voids in these diffusion-controlled reactions required a more rigorous documentation of the role of diffusion in membranes by independent measurements. The transbilayer diffusion of hydrogen peroxide as monitored by occluded catalase activity was developed as a kinetically valid probe to specifically address this question. This in turn led to unique results on the mechanistic basis of stretch (= hypo-osmotic) activation of hydrogen peroxide permeation via such voids. The rate of peroxide permeation is shown to be markedly stretch sensitive in some cells/organelles (e.g. peroxisomes) and insensitive in others (e.g. erythrocytes); this was equally true of liposomes prepared from lipids extracted from the corresponding cells/organelles. The molecular basis of stretch sensitivity was uncovered using specific binary mixtures of lipids: while pure phosphatidyl choline liposomes were stretch insensitive, these became sensitive when doped only with specific lipids, viz. cardiolipin and cerebrosides. Cholesterol abolished this stretch sensitivity in ternary mixtures. Induction of stretch sensitivity by cardiolipin was marked by lowering of activation energy for peroxide diffusion, a negative temperature coefficient for glucose permeation while further addition of cholesterol reversed these phenomena. The steady state fluorescence polarization studies revealed intimate correlations between anisotropy, hydrogen peroxide diffusion, and stretch sensitivity consistent with presence of voids in these binary mixtures.

Animals↗
PubMed1973

Fluid shifts associated with gas-induced osmosis.

It has been proposed that equilibration of nitrous oxide with blood plasma increases osmotic pressure and thereby causes hemodilution. However, calculations show that the 250-torr osmotic gradient produced by 0.7 atmosphere of nitrous oxide dissolved in blood plasma (separated from the other body fluids by a membrane permeable only to water) would be eliminated by a water shift which would dilute the plasma by only 4 percent. Permeability of the membrane to nitrous oxide would further reduce the shift. In vivo measurements confirmed the smallness of any osmotically induced shifts by demonstrating no significant transient changes in hematocrit value when 0.7 atmosphere of nitrous oxide was added to or removed from an inhaled anesthetic mixture in man. These results cast doubt on the suggestions that gas-induced osmosis is an important factor in dysbarism or in clinical anesthesia.

Anesthesia, Inhalation↗
PubMed1984

Osmosis and intermolecular force.

A hypothesis concerning the molecular-dynamical basis of osmosis is presented. According to this hypothesis, osmosis results from the attractive force between solute and water molecules, and the exclusion of the solute from the water transport channels of the membrane. Based on this hypothesis, the osmotic process is predicted to involve a large number of short "spurts" of high magnitude force, with a spurt force per unit area of channel of RT/Vs, where R is the gas constant, T is absolute temperature, and Vs is solute molar volume.

Biological Transport↗
PubMedDate not supplied

[Regeneration of sanitaro-hygienic water during long space flights by reverse osmosis].

Experiments on the purification of wash water by means of reverse osmosis membranes MGA-100 were performed. The membrane selectivity with respect to the major components (catamine AB, amine oxide and sodium chloride) was close to 100% whereas membrane permeability was not lower than 70% that of distilled water. The results of a field study in which 330 1 of repeatedly used wash water were reclaimed showed that reverse osmosis can be effectively employed for that purpose.

Membranes, Artificial↗
PubMed1995

Fluid flow across the jejunal epithelia in vivo elicited by d-c current: effects of mesenteric nerve stimulation.

The aim of this study was twofold: (1) to investigate the effect of electrical gradients on fluid transport across the rat jejunal mucosa in vivo; and (2) to evaluate the effect of mesenteric nerve stimulation (MNS) on current-induced fluid flow. Segments of rat jejunum were mounted with intact blood circulation in an in vivo chamber, allowing parallel registration of net fluid transport rate (NFT) and electrical properties of the tissue. Directed currents (d-c) of varying densities were passed across the jejunal wall in both directions and the current-induced fluid flows were measured. D-c current elicited fluid flows across the jejunal mucosa towards the cathode in both directions in a 'dose-dependent' manner. The effect was markedly greater when the anode was placed on the serosal side (s-->m current) than when it was placed on the mucosal side (m-s current). MNS abolished m-->s current induced flow whereas the effect of s-->m current was not significantly changed. It was concluded that: (1) true electro-osmosis probably accounts for the major portion of current-induced fluid flow in this model; (2) current induced fluid flow is rectified in opposite directions in vivo and in vitro; and (3) MNS inhibits current-induced fluid flow m-->s, possibly via a sympathetic effect on epithelial permeability.

Adrenergic Fibers↗
PubMed1966

Non-linear osmosis.

1. The relation between osmotic gradient and rate of osmotic water flow has been measured in rabbit gall-bladder by a gravimetric procedure and by a rapid method based on streaming potentials. Streaming potentials were directly proportional to gravimetrically measured water fluxes.2. As in many other tissues, water flow was found to vary with gradient in a markedly non-linear fashion. There was no consistent relation between the water permeability and either the direction or the rate of water flow.3. Water flow in response to a given gradient decreased at higher osmolarities. The resistance to water flow increased linearly with osmolarity over the range 186-825 m-osM.4. The resistance to water flow was the same when the gall-bladder separated any two bathing solutions with the same average osmolarity, regardless of the magnitude of the gradient. In other words, the rate of water flow is given by the expression (O(m) - O(s))/[R(o)' + (1/2)k' (O(m) + O(s))], where R(o)' and k' are constants and O(m) and O(s) are the bathing solution osmolarities.5. Of the theories advanced to explain non-linear osmosis in other tissues, flow-induced membrane deformations, unstirred layers, asymmetrical series-membrane effects, and non-osmotic effects of solutes could not explain the results. However, experimental measurements of water permeability as a function of osmolarity permitted quantitative reconstruction of the observed water flow-osmotic gradient curves. Hence non-linear osmosis in rabbit gall-bladder is due to a decrease in water permeability with increasing osmolarity.6. The results suggest that aqueous channels in the cell membrane behave as osmometers, shrinking in concentrated solutions of impermeant molecules and thereby increasing membrane resistance to water flow. A mathematical formulation of such a membrane structure is offered.

Animals↗
PubMed1998

Effect of diffusion potential, osmosis and ion-exchange on transdermal drug delivery: theory and experiments.

Equations expressing the effect of the diffusion potential on the trace ion transfer across a porous charged membrane have been derived. These equations have been tested with experiments with human cadaver skin. The transfer of sotalol and salicylate was measured varying the salt (NaCl) concentration in the donor and receiver compartments. It appears that osmotic pressure and ion-exchange make a significant contribution to the flux enhancement by the diffusion potential.

Administration, Cutaneous↗
PubMed2005

Reversible permeabilization using high-intensity femtosecond laser pulses: applications to biopreservation.

Non-invasive manipulation of live cells is important for cell-based therapeutics. Herein we report on the uniqueness of using high-intensity femtosecond laser pulses for reversibly permeabilizing mammalian cells for biopreservation applications. When mammalian cells were suspended in a impermeable hyperosmotic cryoprotectant sucrose solution, femtosecond laser pulses were used to transiently permeabilize cells for cytoplasmic solute uptake. The kinetics of cells exposed to 0.2, 0.3, 0.4, and 0.5 M sucrose, following permeabilization, were measured using video microscopy, and post-permeabilization survival was determined by a dual fluorescence membrane integrity assay. Using appropriate laser parameters, we observed the highest cell survival for 0.2 M sucrose solution (>90%), with a progressive decline in cell survival towards higher concentrations. Using diffusion equations describing the transport of solutes, the intracellular osmolarity at the inner surface of the membrane (x = 10 nm) and to a diffusive length of x = 10 microm was estimated, and a high loading efficiency (>98% for x = 10 nm and >70% for x = 10 microm) was calculated for cells suspended in 0.2 M sucrose. This is the first report of using femtosecond laser pulses for permeabilizing cells in the presence of cryoprotectants for biopreservation applications.

Animals↗
PubMed2000

Transport of Water and Ions Through a Clay Membrane.

A model for hindered transport of water and ions is used to predict transient flow through a clay membrane caused by an initial difference in the concentration of salt solutions in reservoirs on the two sides of the membrane. Transport is assumed to be controlled by three coefficients, which are analogous to the permeability, salt diffusivity, and salt reflection coefficient of the membrane. Initial fluid motion is caused by osmosis, leading to a buildup of pressure on one side of the membrane. However, the clay forms an imperfect ion exclusion membrane and the final steady state is one of equal concentrations and pressures on the two sides of the membrane. The time-dependent differences in pressure and salt concentration across the membrane are predicted to vary as the sum of two decaying exponentials. When the salt reflection coefficient is small, one time scale governs Darcy flow through the membrane and another the diffusion of salt. Experimental results confirm the analysis. Although the salt concentration in the reservoirs was monitored in the experiments, estimates of the transport coefficients can be obtained by measuring only the pressure change across the membrane. Copyright 2000 Academic Press.

Journal Article↗
PubMed1975

Cation effects on volume and water permeability in the halophilic algae Dunaliella parva.

Rates of change of cell volume were measured in suspensions of the halophilic green algae Dunaliella parva subjected to changes in cation composition and concentration of the outside medium. Measurements were made with a particle size analyzer and results were checked by direct microphotography. For any one salt solution, changes in cell volume with concentration were consistent with the Boyle-Van't Hoff model of an osmometer. Nonosmotic volume comprised 60-80% of total cell volume and was sensitive to the nature of the cation, increasing in the order Cs less than K less than Na less than Ca less than Mg. Kinetics of volume change in response to changes in outside salt concentration are best described by two kinetic coefficients differing by one order of magnitude and dependent on the nature of the outside cation (decreasing in order Cs greater than K greater than Na greater than Mg) as well as on direction of water flow.

Calcium↗
PubMed2006

The role of aquaporin water channels in fluid secretion by the exocrine pancreas.

The mammalian exocrine pancreas secretes a near-isosmotic fluid over a wide osmolarity range. The role of aquaporin (AQP) water channels in this process is now becoming clearer. AQP8 water channels, which were initially cloned from rat pancreas, are expressed at the apical membrane of pancreatic acinar cells and contribute to their osmotic permeability. However, the acinar cells secrete relatively little fluid and there is no obvious defect in pancreatic function in AQP8 knockout mice. Most of the fluid secreted by the pancreas is generated by ductal epithelial cells, which comprise only a small fraction of the gland mass. In the human pancreas, secretion occurs mainly in the intercalated ducts, where the epithelial cells express abundant AQP1 and AQP5 at the apical membrane and AQP1 alone at the basolateral membrane. In the rat and mouse, fluid secretion occurs mainly in the interlobular ducts where AQP1 and AQP5 are again co-localized at the apical membrane but appear to be expressed at relatively low levels. Nonetheless, the transepithelial osmotic permeability of rat interlobular ducts is sufficient to support near-isosmotic fluid secretion at observed rates. Furthermore, apical, but not basolateral, application of Hg(2+) significantly reduces the transepithelial osmotic permeability, suggesting that apical AQP1 and AQP5 may contribute significantly to fluid secretion. The apparently normal fluid output of the pancreas in AQP1 knockout mice may reflect the presence of AQP5 at the apical membrane.

Animals↗
PubMed1987

Intracellular Ca2+ concentration and the antidiuretic hormone-induced increase in water permeability: effects of ionophore A23187 and quinidine.

The hydroosmotic responses induced by oxytocin and 8-bromo-cyclic AMP, in frog and toad urinary bladders, were recorded minute by minute. 3HHO and 45Ca unidirectional fluxes as well as prostaglandin B2 liberation were also measured. It was observed that: (1) Addition of the calcium ionophore A23187 or quinidine to the serosal bath inhibited the response to oxytocin, but not to 8-bromo-cyclic AMP, while increasing prostaglandin E1 liberation into the serosal but not into the mucosal bath. (2) Addition of A23187 to the mucosal bath induced a transient and temperature-dependent inhibition of the response elicited by 8-bromo-cyclic AMP. The time-course of this reduction in water permeability and its sensitivity to medium temperature were similar to those observed after the withdrawal of agonist, but clearly different of those observed after intracellular acidification. (3) The hydroosmotic response was also transitorily inhibited when the Ca2+ concentration was step-changed in the mucosal bath. (4) When added to the mucosal or to the serosal baths, the ionophore increased either the apical or the laterobasal Ca2+ permeabilities. It is concluded that manipulation of intracellular Ca2+ interferes with the hydroosmotic response at two different levels. (1) A first target point located 'pre-cyclic-AMP production'. This effect would be mediated by prostaglandin liberation. (2) A second target point located after cyclic AMP production and before the 'temperature-dependent rate-limiting step'. This effect is probably related to the mechanism controlling the insertion and removal of water channels.

8-Bromo Cyclic Adenosine Monophosphate↗
PubMed1988

Cryomicroscope investigation and thermodynamic modeling of the freezing of unfertilized hamster ova.

Thermodynamic computer modeling was used to predict the freezing response of single-celled unfertilized hamster ova. The cell membrane transport characteristics were investigated, using a microscope diffusion chamber system. The mean osmotically inactive cell volume was determined to be 21.6% of the initial cell volume. An overall mean value of 0.8 +/- 0.1 micron3/micron2.min.atm (= 18 +/- 2.5 micron/sec) was determined for the membrane hydraulic coefficient, Lp. The effect of the extracellular solute concentration on Lp was determined at room temperature (approximately 23 degrees C). A thermodynamic computer model was used to predict the cell response to freezing. The predicted response was compared to the actual volumetric response observed during freezing on a temperature-controlled cryomicroscope conduction stage. The effect of the cooling rate on the nucleation temperature of unprotected ova and protected ova suspended in a 1.5 M DMSO solution was investigated. Overall mean nucleation temperatures of -13 and -57.1 degrees C were observed for unprotected and protected ova, respectively, where the mean nucleation temperature for protected ova was strongly cooling rate dependent.

Animals↗