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At least 505 records · Page 28Linked to original sources
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↗
PubMed2006

Epithelial fluid transport: protruding macromolecules and space charges can bring about electro-osmotic coupling at the tight junctions.

The purpose of the present work is to investigate whether the idea of epithelial fluid transport based on electro-osmotic coupling at the level of the leaky tight junction (TJ) can be further supported by a plausible theoretical model. We develop a model for fluid transport across epithelial layers based on electro-osmotic coupling at leaky tight junctions (TJ) possessing protruding macromolecules and fixed electrical charges. The model embodies systems of electro-hydrodynamic equations for the intercellular pathway, namely the Brinkman and the Poisson-Boltzmann differential equations applied to the TJ. We obtain analytical solutions for a system of these two equations, and are able to derive expressions for the fluid velocity profile and the electrostatic potential. We illustrate the model by employing geometrical parameters and experimental data from the corneal endothelium, for which we have previously reported evidence for a central role for electro-osmosis in translayer fluid transport. Our results suggest that electro-osmotic coupling at the TJ can account for fluid transport by the corneal endothelium. We conclude that electro-osmotic coupling at the tight junctions could represent one of the basic mechanisms driving fluid transport across some leaky epithelia, a process that remains unexplained.

Animals↗
PubMed2003

Community structure of microbial biofilms associated with membrane-based water purification processes as revealed using a polyphasic approach.

The microbial communities of membrane biofilms occurring in two full-scale water purification processes employing microfiltration (MF) and reverse osmosis (RO) membranes were characterized using a polyphasic approach that employed bacterial cultivation, 16S rDNA clone library and fluorescence in situ hybridization techniques. All methods showed that the alpha-Proteobacteria was the largest microbial fraction in the samples, followed by the gamma-Proteobacteria. This suggested that members of these two groups could be responsible for the biofouling on the membranes studied. Furthermore, the microbial community structures between the MF and RO samples were considerably different in composition of the most predominant 16S rDNA clones and bacterial isolates from the alpha-Proteobacteria and only shared two common groups ( Bradyrhizobium, Bosea) out of more than 17 different bacterial groups observed. The MF and RO samples further contained Planctomycetes and Fibroacter/ Acidobacteria as the second predominant bacterial clones, respectively, and differed in minor bacterial clones and isolates. The community structure differences were mainly attributed to differences in feed water, process configurations and operating environments, such as the pressure and hydrodynamic conditions present in the water purification systems.

Alphaproteobacteria↗
PubMed2001

Biodegradation of synthetic and naturally occuring mixtures of mono-cyclic aromatic compounds present in olive mill wastewaters by two aerobic bacteria.

Two bacterial strains, Ralstonia sp. LD35 and Pseudomonas putida DSM 1868, were assayed for their ability to degrade the monocyclic aromatic compounds commonly found in olive mill wastewaters (OMWs). The goal was to study the possibility of employing the two strains in the removal of these recalcitrant and toxic compounds from the effluents of anaerobic treatment plants fed with OMWs. At first, the two strains were separately assayed for their ability to degrade a synthetic mixture of nine aromatic acids present in OMWs, both in growing- and resting-cell conditions. Then, due to the complementary activity exhibited by the two strains, a co-culture of the two bacteria was tested under growing-cell conditions for degradation of the same synthetic mixture. Finally, the degradation activity of the co-culture on two fractions was studied. Both fractions one deriving from natural OMWs through reverse osmosis treatment and containing low-molecular weight organic molecules, and the other obtained from an anaerobic lab-scale treatment plant fed with OMWs, were rich in monocyclic aromatic compounds. The co-culture of the two strains was able to biodegrade seven of the nine components of the tested synthetic mix (2, 6-dihydroxybenzoic acid and 3, 4, 5-trimethoxybenzoic acid were the two undegraded compounds). In addition, an efficient biodegrading activity towards several aromatic molecules present in the two natural fractions was demonstrated.

Bacteria, Aerobic↗
PubMed2006

Monitoring of distribution water qualities under various source water blending.

The main goal of this large-scale pilot distribution study was to systematically investigate the impacts of blending different source waters on distribution water qualities. The principal source waters investigated were conventionally treated ground water (G1), surface water processed by enhanced treatment (S1), and desalted seawater by reverse osmosis membranes (RO). Due to the nature of raw water quality and associated treatment processes, G1 water had high alkalinity, while S1 and RO sources were characterized as high sulfate and high chloride waters, respectively. One year of pilot pipe study demonstrated that water quality was significantly deteriorated by increased color when source water blends with characteristics different from historic groundwater were introduced to pipe distribution systems. Elevated color was associated with release of iron corrosion products, mainly from aged unlined cast iron pipes. Iron release increased significantly when exposed to RO and S1 waters: that is, the greater iron release was experienced with alkalinity reduced below the background of G1 water. Lead and copper release to water, on the other hand, enhanced with the application of RO and G1 waters, respectively.

Alkalies↗
PubMed1985

The effect of procedures intended to alter the interstitial fluid pressure in the sockets of resected rat incisors on their eruption rate.

Eruption rates of resected incisors were measured while their sockets were kept open to the mouth. In other resected incisors, hypertonic solutions were placed in the pulp cavity, with the intention of drawing fluid by osmosis across the membrane separating the pulp cavity from the socket, to lower the pressures within the socket. These procedures slowed eruption when control resected incisors were erupting rapidly but not during their initial and final slow phases of eruption. The findings are consistent with there being two factors making resected incisors erupt, tentatively identified as the periodontal ligament and, when eruption is rapid, the interstitial pressures of the tissues in the socket.

Albumins↗
PubMed1977

Formation of electrical field accompanying temperature jump in isolated spinach chloroplasts.

Temperature-jump-induced absorbance changes of spinach chloroplasts in the dark were studied. After the temperature rise, a fast absorbance decrease and a succeeding slow absorbance increase were observed at the wavelength of 515 nm. The spectrum of the fast phase had positive maxima (increase in absorbance) at 430, 470 and 673 nm and a negative maxima (decrease in absorbance) at 525 nm. Permeant ions, tetraphenylboron-, tetraphenylarsonium+, and tetraphenylphosphonium+, decreased the extent of the fast absorbance change and increased the rate of slow recovery. Additions of inorganic potassium salts had a similar effect. Valinomycin, added in the presence of potassium ion, also increased the rate of slow recovery. These ions and ionophore had a parallel effect also on the recovery of flash-induced 515-nm absorbance change in chloroplasts. Electroneutral nigerericin did not affect the temperature-jump-induced absorbanc change. These results suggest the formation of electrical field across the thylakoid membrane in the dark accompanying the temperature rise. A possible involvement of the movement of water molecules (thermo-osmosis) in the observed absorbance changes is also discussed.

Chloroplasts↗
PubMed1985

Respiration induces variable porosity to polyols in the mitochondrial inner membrane.

The osmotic basis of low and high amplitude swelling in mitochondria was investigated in detail using sucrose and mannitol as external osmolytes. Osmotic behaviour of mitochondria in various respiratory states was consistent with significant changes in the porosity of the inner membrane corresponding to the rate of respiration. The stoichiometry of oxidative phosphorylation was confirmed to be dependent on the physical state (i.e., osmotic stretch) of the inner membrane regardless of the external polyol used. High amplitude swelling in polyol media was shown to arise from a sequential disruption of the outer and inner mitochondrial membranes, due to a dynamic instability induced by a combination of respiration, unscreened (fixed) surface charge density and the consequent variable porosity of the inner membrane. These novel experimental findings based on the physical theory of osmosis emphasize the need to define the fine structural changes of the inner membrane associated with oxidative phosphorylation to arrive at a comprehensive mechanism.

Animals↗
PubMed1978

Distribution of osmotic flow in stomach and gallbladder.

Stomach and gallbladder actively transport fluids which are nearly isotonic to plasma. Consideration of the measured areas of the appropriate transporting surfaces gives a more realistic view of the osmotic gradient required to account for the observed net flow of water. Simple osmosis may be adequate if the transporting membrane has an osmotic permeability in the range observed for synthetic lecithin-cholesterol bilayer membranes.

Animals↗
PubMed1978

Local osmotic coupling to the active trans-endothelial bicarbonate flux in the rabbit cornea.

The present experiments investigate HCO3-, Cl- and fluid fluxes across partially destromalised corneas. Although there is no net flux of Cl-, there is a net flux of HCO-3 across the endothelium from stromal side to aqueous side which is accompanied by a flux of water in the same direction. Bulk phase osmosis cannot account for the initiation of the flux of fluid. Local osmotic coupling between ions and water is postulated to occur in the preparation. The exudate is hypertonic to the bathing Ringer solution.

Animals↗
PubMed1995

Effects of systemic and local ethanol on responses of rat cerebellar Purkinje neurons to iontophoretically applied gamma-aminobutyric acid.

The goals of this study were: (1) to determine the effects of acute systemic or local application of ethanol (ETOH) on the response of cerebellar Purkinje cells (P-cells) to iontophoretically applied gamma-aminobutyric acid (GABA) and (2) to characterize the effects of Ro15-4513, a putative antagonist of ETOH-GABA interactions, on ETOH-induced changes in GABA responsiveness. Male Sprague-Dawley rats (230-370 g) were anesthetized with halothane and implanted with intraperitoneal catheters for administration of ETOH (1.0-2.0 g/kg), before the recording session. Extracellular activity of single P-cells was recorded with the central barrel of a five-barrel micropipette, the other barrels of which were used for microiontophoresis of GABA and electro-osmosis of ETOH at the recording site. Spontaneous discharge and response of P-cells to GABA were monitored during a pre-ETOH control and for 1-1.5 h after systemic or electro-osmotic administration of ETOH. Transient suppression of spontaneous P-cell discharge was usually observed within 4-8 min of systemic ETOH injection. This effect lasted 2-4 min in 10 out of 19 rats tested. GABA-mediated inhibitory responses of cerebellar P-cells were increased by 45-50% relative to pre-ETOH values at 10 and 90 min post-ETOH injection. Prior administration of the imidazobenzodiazepine Ro15-4513 (4-6 mg/kg) failed to antagonize either the ETOH-induced enhancement of GABA-mediated inhibition or the transient inhibition of spontaneous P-cell activity rat cerebellar P-cell produced by ETOH. In these studies, electro-osmotically applied ETOH produced a potent suppression of spontaneous P-cell activity which precluded further augmentation of unit responses to GABA. These results show that doses of systemically administered ETOH which are mildly intoxicating in the awake, behaving animal, enhance the inhibitory action of GABA on cerebellar P-cell discharge.

Action Potentials↗
PubMed1994

Water transport across biological membranes.

The rate of the lateral diffusion of straight-chain phospholipids predicts the rate of water diffusion through bilayers. A new model of lipid dynamics integrates these processes. Substances such as cholesterol that reduce water diffusion proportionally reduce lateral diffusion. The model yields a number of predictions about the dynamics of the lipids at the Tm and suggests different mechanisms for how water diffuses across bilayers of other-than-straight-chain lipids, and how proteins bind to membranes. A second recent development in water transport across biological membranes is the discovery of a ubiquitous family of water transport proteins that facilitate large-volume water translocation. Like water diffusion through lipid bilayers, water transport by these proteins is directed by osmosis and is therefore under the control of ATP and ion pumps. The presence of water transport proteins in membranes is often regulated by hormones.

Biological Transport↗
PubMed1992

A study of nutritional transport in capillary-tissue exchange system.

A two region flow model has been developed for a capillary-tissue exchange unit. Nutrient dissolved in plasma enters into the tissue from capillary through diffusion, filtration and osmosis. The governing non-linear coupled partial differential equations in the two regions (capillary and tissue) have been solved separately with suitable boundary and matching conditions. The results for the variation of Taylor's-Diffusivity Coefficient and concentration of a nutrient in the tissue region have been brought out for various values of the parameters involved in the analysis and discussed. It has been particularly noted that the penetration depth in the tissue for the nutritional transport can be considered as an important diagnostic parameter for many cardiovascular diseases.

Biological Transport↗
PubMed1984

Extracellular fluid filtration as the reason for the viscoelastic behaviour of the passive myocardium.

The experimental results are described confirming the hypothesis that the viscous properties of the passive cardiac muscle are connected with the extracellular fluid filtration in the elastic medium formed by the connective tissue network and myocytes. It is shown that the relaxation properties are more pronounced in cold-blooded animals myocardium (frog, turtle) than in that of warm-blooded (cat, rabbit), which correlates with the smaller connective tissue content and larger porosity of myocardium in cold-blooded animals. The decrease in porosity of the cardiac muscle samples by reducing the osmosis of the surrounding solution or squeezing the fluid out of the samples by mechanical torsion results in the slowing down of the stress relaxation, the increase in porosity of the muscle in the hyperosmotic solution results in its speeding up. The increase of the surrounding solution viscosity by adding saccharose to it leads to the proportional stress relaxation deceleration, which agrees quantitatively and qualitatively with the advanced hypothesis.

Animals↗
PubMed1989

Lamicel does not promote induction of labour. A randomized controlled study.

Lamicel is a synthetic tent, which, when inserted in the cervical canal, dilates the cervix by osmosis. Lamicel as an adjunct to induction of labour with intravenous oxytocin or vaginal prostaglandin E2 has been examined in a randomized controlled trial. Ninety-one pregnant women with an unripe cervix participated in the study. No improvement in efficacy was observed in the Lamicel groups compared to the control groups, neither when induction of labour was performed with oxytocin nor with vaginal prostaglandin.

Apgar Score↗
PubMed1982

New polyacrylamide matrices for drift-free isoelectric focusing.

The major cause for pH gradient decay and cathodic drift during isoelectric focusing in polyacrylamide gels has been found to be electroendo-osmotic flow generated by fixed charges in the gel matrix. These changes have the following causes: (a) trace impurities of acrylic acid in the co-monomers; (b) covalent incorporation of catalysts (persulphate and riboflavin 5'-phosphate) as terminal groups in polyacrylamide chains; (c) hydrolysis of amide groups to acrylic acid in the gel layer underneath the cathodic filter paper strip. The result of these fixed negative charges in the matrix is a movement of counter-ions with hydration water towards the cathode (i.e. electroendo-osmosis) with concomitant drift of pH gradient and focused protein zones in the same direction. It is impossible to cure the cathodic drift by increasing the pH of the anolyte, or decreasing the pH of the catholyte, or both, as previously suggested. One way to reduce the cathodic drift efficiently is to incorporate covalently in the matrix tertiary or quaternary groups (3-dimethylaminopropylmethacrylamide) in stoichiometric amounts as compared with the negative charges. This 'balanced' polyacrylamide displays zero drift for at least 5000 V.h, which is considered to be an ample time for equilibrium separation of protein species in isoelectric focusing.

Chemical Phenomena↗
PubMed1990

False-positive gram-stained smears of sterile body fluids due to contamination of laboratory deionized water.

Bacterial contamination of staining reagents led to false-positive smears from clinical samples. Piped deionized water used to make up the staining reagents was found to be the source of contamination. The closed loop system supplying the deionized water was decontaminated with hydrogen peroxide and upgraded by addition of a reverse osmosis unit and bacterial filter. No subsequent contamination has been demonstrated.

Bacterial Infections↗
PubMed1993

Occurrence of endotoxin in dialysis fluid from 39 dialysis units.

Endotoxin exposure during haemodialysis may cause acute and chronic adverse reactions. In order to estimate the risk to the patient, samples of dialysis fluid from 39 of the 45 dialysis units in Sweden were analysed by the chromogenic Limulus amoebocyte lysate assay. Higher levels were obtained after the usual weekend shutdowns. The length of the tubing delivering the reverse osmosis water seemed to influence the extent of contamination. Fifty-nine percent of the units showed low mean endotoxin levels (i.e. mean concentration below the recommended limit in Sweden: < 25 ng l-1), while 18% of units had high levels (mean concentration > 100 ng l-1).

Endotoxins↗