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Coupling of water to solute movement in isolated gastric mucosa.

Osmosis is apparently the mechanism responsible for the coupling of water to solute transport in biological membranes. Often a secreted or absorbed fluid is essentially iso-osmotic with the solution of origin, or with plasma, and various models have been constructed by Curran, Diamond and others to account for such observations. More information is needed, however, to test further the predictions of these models and to facilitate correlation with known structural details. This study deals with gastric secretion and the effects of the luminal solution on its composition. Although pure gastric juice collected in vivo is virtually iso-osmotic with plasma, Teorell, Obrink and others found that instillation of a buffer solution (glycine) in the lumen led to a twofold increase in the concentration of gastric acid. This effect is not restricted to buffer solutions: the normality of H+ secreted into an isotonic (120 mM) NaCl solution bathing the isolated bullfrog gastric mucosa was 276 +/- 19 mmol/1 (13 experiments). Clearly the luminal solution affects the concentration of gastric secretion, probably by reducing an endogenous osmotic gradient. Thus the sites responsible for transport of H+ must be accessible from the luminal solution.

Animals↗

Fluid transport across airway epithelia.

Active ion transport across the surface epithelium of dog trachea results in fluid transport. The direction and amount of fluid transported may depend on a balance between active chloride secretion and active sodium absorption. In contrast, fluid movement across submucosal gland epithelium does not seem to depend on active salt transport. Instead, water may be drawn into the duct lumen by simple osmosis after the release of the osmotically active contents of secretory granules. Cell culture may provide a means of studying the secretory properties of the individual cell types of airway epithelia. We have produced primary monolayer cultures of cells from dog tracheal epithelium which retain the differentiated salt and water transport of the original tissue.

Animals↗

Osmotic flow in membrane pores of molecular size.

Water transfer by osmosis through pores occurs either by viscous flow or diffusion depending on whether the driving osmolyte is able to enter the pore. Analysis of osmotic permeabilities (Pos) measured in antibiotic and cellular pore systems supports this distinction, showing that Pos approaches either the viscous value (Pf) or the diffusive value (Pd) depending on the size of the osmolyte in relation to the pore radius. Macroscopic hydrodynamics and diffusion theory, when used with drag and steric coefficients within an appropriate osmotic model, apply with remarkable accuracy to channels of molecular dimensions where water molecules cannot pass each other, without the need to postulate any special flow regimens. It becomes apparent that the true viscous to diffusive flow ratio, Pf/Pd, can be separated from the effects of tracer filing by osmotic measurements alone. It does not monotonically decrease with the pore radius but rises steeply at the smaller radii which would apply to pores in cell membranes. Consequently, the application of the theory to osmotic and diffusive flow data for the red cell predicts a pore radius of 0.2 nm in agreement with other recent measurements on isolated components of the system, showing that the viscous-diffusive distinction applies even in molecular pores.

Anti-Bacterial Agents↗

Salt-water coupling in leaky epithelia.

The theory of quasi-isotonic transport by cellular osmosis (the standing-gradient theory) has been challenged on the grounds that the osmotic permeabilities of the mucosal and interspace membranes are too low; if they were as high as the theory requires then the osmotic permeability of the whole epithelium would be 2-3 orders of magnitude higher than observed. This objection has basically been accepted for it is now claimed that these enormous permeabilities do exist, but are masked by unstirred-layer effects; I show that this is incorrect because unstirred-layer corrections are small and that the situation has not changed since 1975. The view that the route of fluid transport is junctional is replacing the cellular theory, and trans-junctional water flows seem to account for major fractions of the flow in various epithelia. I argue on grounds of general theory that these are unlikely to be osmotic flows because the junctional pores cannot satisfy both the osmotic and diffusive properties required of them, but the basic osmotic theory is also rather vague here. Non-osmotic theories, if junctional flow is accepted, must be either electro-kinetic or peristaltic.

Animals↗

Volume flows across gallbladder epithelium induced by small hydrostatic and osmotic gradients.

The hydraulic conductivity of rabbit gallbladder epithelium has been studied using a continuous volumetric method based on capacitance measurements. The time resolution for measuring osmotic flows is in the range of seconds. Volume flows have been induced by osmotic gradients between 0 and 100 mosmol. In this range the flow-force relation is linear and the Pf value is 9.3 X 10(-3) cm/sec. After correction for solute polarization effects, the Pf value amounts to 0.05 cm/sec. The observed flow is constant between 5 sec up to 20 min after a sudden increase in the osmolarity of the mucosal solution. The wet weight of the gallbladder tissue decreases by 22% and increases by 30% during osmotic flows from mucosa to serosa, respectively. Volume flows induced by hydrostatic pressure gradients on the mucosal surface are linearly related to the driving forces between 0 and 40 mbar. The Pf value is 0.15 cm/sec. The volume flows are constant between 2 sec and 15 min after pressure application. The flow-force relation for pressure gradients on the serosal surface is markedly nonlinear for gradients greater than 5 mbar. Below 5 mbar the Pf value is 4.5 cm/sec. From electrical measurements, e.g., resistance and streaming potentials, and from flux studies with inulin and polyethylene glycol 4000, it is concluded that hydrostatic and osmotic gradients are not comparable when they are applied to gallbladder epithelium. They induce volume flows across different pathways, e.g., osmosis predominantly across the cellular route and pressure filtration predominantly across paracellular routes.

Animals↗

Osmotic gradient dependence of osmotic water permeability in rabbit proximal convoluted tubule.

To assess steady-state transepithelial osmotic water permeability (Pf), rabbit proximal convoluted tubules were perfused in vitro with the impermeant salt, sodium isethionate at 26 degrees C. Osmotic gradients (delta pi) were established by varying the bath concentration of the impermeant solute, raffinose. When lumen osmolality was 300 mOsm and bath osmolality was 320, 360 and 400 mOsm, apparent Pf decreased from 0.5 to 0.10 to 0.08 cm/sec, respectively. Similar data were obtained when lumen osmolality was 400 mOsm. Five possible causes of the delta pi dependence of apparent Pf were considered experimentally and/or theoretically: (1) external unstirred layer (USL); (2) cytoplasmic USL; (3) change in surface area; (4) saturation of water transport; (5) down-regulation of Pf. Apparent Pf was inhibited 83% by p-chloromercuribenzene sulfonate (pCMBS) at 20 mOsm, but not at 60 mOsm delta pi, suggesting presence of a serial barrier resistance to water transport. Increases in perfusate or bath solution flow rate and viscosity did not alter apparent Pf, ruling out an external USL. A simple cytoplasmic USL, described by a constant USL thickness and solute diffusion coefficient, could not account for the delta pi dependence of apparent Pf according to a mathematical model. The activation energy (Ea) for apparent Pf increased from 7.0 to 12.5 kcal/mol when delta pi was increased from 20 to 60 mOsm, not consistent with a simple USL or a change in membrane surface area with transepithelial water flow. These findings are most consistent with a complex cytoplasmic USL, where the average solute diffusion coefficient and/or the area available for osmosis decrease with increasing delta pi. These results (1) indicate that true Pf (at physiologically low delta pi) is very high (greater than 0.5 cm/sec) in the rabbit proximal tubule; (2) provide an explanation for the wide variation in Pf values reported in the literature using different delta pi, and (3) suggest the presence of a flow-dependent cytoplasmic barrier to water flow.

4-Chloromercuribenzenesulfonate↗

Nature of the water channels in the internodal cells of Nitellopsis.

The hydraulic resistance was measured on internodal cells of Nitellopsis obtusa using the method of transcellular osmosis. The hydraulic resistance was approximately 2.65 pm-1 sec Pa, which corresponds to an osmotic permeability of 101.75 microns sec-1 (at 20 degrees C). p-Chloromercuriphenyl sulfonic acid (pCMPS) (0.1-1 mM, 60 min) reversibly increases the hydraulic resistance in a concentration-dependent manner. pCMPS does not have any effect on the cellular osmotic pressure. pCMPS increases the activation energy of water movement from 16.84 to 32.64 kJ mol-1, indicating that it inhibits water movement by modifying a low resistance pathway. pCMPS specifically increases the hydraulic resistance to exosmosis, but does not influence endosmosis. By contrast, nonyltriethylammonium (C9), a blocking agent of K+ channels, increases the hydraulic resistance to endosmosis, but does not affect that to exosmosis. These data support the hypothesis that water moves through membrane proteins in characean internodal cells and further that the polarity of water movement may be a consequence of the differential gating of membrane proteins on the endo- and exoosmotic ends.

4-Chloromercuribenzenesulfonate↗

Single water channels of aquaporin-1 do not obey the Kedem-Katchalsky equations.

The Kedem-Katchalsky (KK) equations are often used to obtain information about the osmotic properties and conductance of channels to water. Using human red cell membranes, in which the osmotic flow is dominated by Aquaporin-1, we show here that compared to NaCl the reflexion coefficient of the channel for methylurea, when corrected for solute volume exchange and for the water permeability of the lipid membrane, is 0.54. The channels are impermeable to these two solutes which would seem to rule out flow interaction and require a reflexion coefficient close to 1.0 for both. Thus, two solutes can give very different osmotic flow rates through a semi-permeable pore, a result at variance with both classical theory and the KK formulation. The use of KK equations to analyze osmotic volume changes, which results in a single hybrid reflexion coefficient for each solute, may explain the discrepancy in the literature between such results and those where the equations have not been employed. Osmotic reflexion coefficients substantially different from 1.0 cannot be ascribed to the participation of other 'hidden' parallel aqueous channels consistently with known properties of the membrane. Furthermore, we show that this difference cannot be due to second-order effects, such as a solute-specific interaction with water in only part of the channel, because the osmosis is linear with driving force down to zero solute concentration, a finding which also rules out the involvement of unstirred-layer effects. Reflexion coefficients smaller than 1.0 do not necessitate water-solute flow interaction in permeable aqueous channels; rather, the osmotic behaviour of impermeable molecular-sized pores can be explained by differences in the fundamental nature of water flow in regions either accessible or inaccessible to solute, created by a varying cross-section of the channel.

Aquaporin 1↗

Na+ recirculation and isosmotic transport.

The Na(+) recirculation theory for solute-coupled fluid absorption is an expansion of the local osmosis concept introduced by Curran and analyzed by Diamond & Bossert. Based on studies on small intestine the theory assumes that the observed recirculation of Na(+) serves regulation of the osmolarity of the absorbate. Mathematical modeling reproducing bioelectric and hydrosmotic properties of small intestine and proximal tubule, respectively, predicts a significant range of observations such as isosmotic transport, hyposmotic transport, solvent drag, anomalous solvent drag, the residual hydraulic permeability in proximal tubule of AQP1 (-/-) mice, and the inverse relationship between hydraulic permeability and the concentration difference needed to reverse transepithelial water flow. The model reproduces the volume responses of cells and lateral intercellular space (lis) following replacement of luminal NaCl by sucrose as well as the linear dependence of volume absorption on luminal NaCl concentration. Analysis of solvent drag on Na(+) in tight junctions provides explanation for the surprisingly high metabolic efficiency of Na(+) reabsorption. The model predicts and explains low metabolic efficiency in diluted external baths. Hyperosmolarity of lis is governed by the hydraulic permeability of the apical plasma membrane and tight junction with 6-7 mOsm in small intestine and < or = 1 mOsm in proximal tubule. Truly isosmotic transport demands a Na(+) recirculation of 50-70% in small intestine but might be barely measurable in proximal tubule. The model fails to reproduce a certain type of observations: The reduced volume absorption at transepithelial osmotic equilibrium in AQP1 knockout mice, and the stimulated water absorption by gallbladder in diluted external solutions. Thus, it indicates cellular regulation of apical Na(+) uptake, which is not included in the mathematical treatment.

Animals↗

Correlation between transepithelial Na+ transport and transepithelial water movement across isolated frog skin (Rana esculenta).

In the present work the coupling under short-circuited conditions between the net Na(+)-influx across isolated frog skin and the transepithelial transport of water was examined i.e., the short-circuit current (Isc) and the transepithelial water movement (TEWM) were measured simultaneously. It has been shown repeatedly that the Isc across isolated frog skin is equal to the net transepithelial Na+ transport. Furthermore the coupling between transepithelial uptake of NaCl under open-circuit conditions and TEWM was also measured. The addition of antidiuretic hormone (AVT) to skins incubated under short-circuited conditions resulted in an increase in the Isc and TEWM. Under control conditions Isc was 9.14 +/- 2.43 and in the presence of AVT 45.9 +/- 7.3 neq cm-2 min-1 (n = 9) and TEWM changed from 12.45 +/- 4.46 to 132.8 +/- 15.8 nL cm-2 min-1. The addition of the Na+ channel blocking agent amiloride resulted in a reduction both in Isc and TEWM, and a linear correlation between Isc and TEWM was found. The correlation corresponds to that 160 +/- 15 (n = 7) molecules of water follow each Na+ across the skin. In another series of experiments it was found that there was a linear correlation between Isc and the increase in apical osmolarity needed to stop the TEWM. The data presented indicate that the observed coupling between the net transepithelial Na+ transport and TEWM is caused by local osmosis.

Animals↗

Inhibition of NMDA-evoked electrophysiological activity by ethanol in selected brain regions: evidence for ethanol-sensitive and ethanol-insensitive NMDA-evoked responses.

Our laboratory has previously shown that systemically administered ethanol inhibits NMDA-evoked electrophysiological activity in some, but not all, neurons in the medial septum. In the present report, it was found that ethanol, when applied locally via electro-osmosis, potently inhibited NMDA-evoked neuronal activity in a current-dependent manner in the inferior colliculus and hippocampus. In contrast, locally applied ethanol failed to inhibit NMDA-evoked activity in the lateral septum. The inhibition by ethanol of NMDA-evoked activity in the inferior colliculus was specific, in that ethanol failed to inhibit neuronal activity of the inferior colliculus evoked by the excitatory neurotransmitter glutamate. These findings indicate that ethanol can specifically inhibit NMDA-evoked activity in vivo via a local action, and that the ability of ethanol to inhibit NMDA-evoked activity varies regionally in brain. The possibility that these results are explained by the existence of two types of NMDA receptors, one sensitive to ethanol, the other insensitive to ethanol, is discussed.

Animals↗

Aspects of the haemolytic reaction induced by Kanagawa haemolysin of Vibrio parahaemolyticus.

Vibrio parahaemolyticus, an important enteric pathogen, produces toxin (Kanagawa haemolysin, KH), the presence of which correlates well with pathogenicity. KH induced lysis of human red blood cells (HRBC); the kinetics were strongly dependent on KH concentration (0-1 HU/ml) and rather independent of target cell concentration [0.5 < or = haematocrit (%) < or = 6] and the ratio KH:HRBC. The suggestion that KH-induced haemolysis is due to colloid osmosis is supported by results indicating: (1) osmotic protection (by suspension in iso-osmotic choline chloride, D-sorbitol or L-valine, or MOPS-buffered saline with added sucrose), (2) a cell volume increase prior to lysis, and (3) an increase in HRBC cation (86Rb+) influx after KH addition, indicating raised passive cation permeation. The effect of temperature on KH-induced haemolysis indicates the importance of processes other than the action of a simple water-filled pore, because of the high activation energy [53.30 +/- 2.79 kJ (mol.)-1] involved. Although haemolytic rate was attenuated by washout after 5 min KH exposure, the KH-induced lesion itself was not susceptible to washout by either extracellular volume expansion (at constant osmolarity) or centrifugation/resuspension. This suggests that HRBC binding of KH from aqueous solution still continues after 5 min exposure at 37 degrees C. Pre-vortexing KH with dibutyl phthalate (DBP) dramatically reduced the haemolytic activity of the aqueous toxin preparation, suggesting a protein-lipid interaction, which may support the contention that KH can move from a hydrophilic to a hydrophobic environment. Two features were identified that are characteristic of highly purified TDH preparations: (1) thermostability of haemolysin, and (2) monovalent cation selectivity series of lesion: Cs+ > Li+ > K+ > Rb+ > Na+, confirming that TDH is the important leak-inducing agent of KH.

Adult↗

Linear free energy relationship for osmotic water flow through a membrane.

A linear free-energy relationship has been found for the osmotic water flux through membranes in a broad variety of systems including electrolytes, organic compounds, intact biological cells and industrial scale filtration. In all cases, broad concentration ranges were found in which the equation 1n v = alpha 1n m + beta (v, flux (in kg cm-2 min-1; m, molarity] was valid. The parameters alpha and beta were interpreted in terms of molecular weight, mean ionic radius, enthalpy of solvation, electronic structure and H-bonding propensity. The equation is independent of the membrane material and of the presence of other solutes and precipitates, as long as the latter are incompressible. Its parameters are only slightly dependent upon the temperature. The contributions from different solutes to the osmotic flux are at appreciable concentrations even additive. The relationship permits the prediction of the osmotic water flux and of the rate of filtration of systems of known composition. For simple systems it permits determination of the molecular weight, mean ionic radius, degree of hydration and enthalpy of solvation. It is suggested that osmosis is primarily due to the shift of hydration equilibria and that guanidine hydrochloride, in a realistic concentration range, forms practically infinite clathrates with water. The properties of the urea and Gdn X HCl systems indicate that these solutes either reversibly change the membrane structure and/or display intrinsic hysteresis.

Animals↗

Regulation of amniotic fluid volume: intramembranous solute and volume fluxes in late gestation fetal sheep.

OBJECTIVE: Recent studies suggest that amniotic fluid volume is regulated by the rate of intramembranous absorption of amniotic fluid into fetal blood. The purpose of the present study was to determine the simultaneous intramembranous solute and water fluxes to gain insight into the intramembranous transport and amniotic fluid volume regulatory mechanisms. STUDY DESIGN: All major amniotic inflows and outflows, except intramembranous flow, were eliminated in 10 fetal sheep over 8 hours by occlusion of the fetal trachea and esophagus; the fetal urine was drained to the exterior. Amniotic fluid composition and volume were measured before and at the end of the 8 hours. Solute and volume fluxes through the intramembranous pathway were calculated from amniotic fluid concentration and volume changes. Statistical analyses included t-tests, linear regression, and analyses of variance. RESULTS: Amniotic fluid volume decreased by 128 +/- 24 (SE) mL over 8 hours (P < .001), which was correlated only marginally with the fetal to amniotic fluid osmotic gradient (r=0.59; P = .072). Amniotic fluid sodium, chloride, calcium, and bicarbonate concentrations increased (P < .0001), even though there were net outward fluxes of these solutes; these outward fluxes occurred against concentration gradients; and the clearances of these solutes were the same despite widely differing amniotic fluid concentrations and fetal blood to amniotic fluid concentration gradients. With the use of multivariate regression, intramembranous solute fluxes separated into 2 components, which were a primary outward flux that correlated with the volume flux and a minor inward component that correlated with the fetal plasma to amniotic fluid concentration gradient for sodium, chloride, calcium (P < .001), and bicarbonate (P < .02). The concentration-dependent fluxes averaged approximately one third of the bulk fluxes and were in the opposite direction. CONCLUSION: The poor correlation of amniotic fluid volume reduction with the fetal-to-amniotic fluid osmotic gradient shows that the primary mechanism that mediates intramembranous volume flow is not passive osmosis in the normal fetus under basal conditions. The strong correlations of solute fluxes simultaneously with volume flux and concentration gradients suggest that intramembranous solute fluxes are mediated by both bulk flow and passive diffusion. The small size of the passive component relative to the size of the bulk component suggests that intramembranous solute transfer is mediated primarily by bulk flow with a smaller and usually oppositely directed contribution by diffusion down concentration gradients. Bulk flow by vesicular transport is the only known physiologic transport mechanism that is compatible with these data, but it is not known whether this occurs in the amnion or intramembranous blood vessels or both.

Amniotic Fluid↗

Comprehensive characterization of oil refinery effluent-derived humic substances using various spectroscopic approaches.

Refinery effluent-derived humic substances (HS) are important for developing refinery effluent reclamation techniques and studying the environmental chemistry of wastewater effluents. In this study, dissolved organic matter (DOM) from refinery effluent was concentrated using a portable reverse osmosis (RO) system. HS were isolated from RO retentates with XAD-8 resin. A variety of approaches such as specific UV absorbance at 254nm (SUV(254)), elemental analysis, size exclusion chromatography (SEC), solid-state cross polarization magic angle spinning (13)C nuclear magnetic resonance spectrometry ((13)C CPMAS NMR), Fourier transform infrared spectrometry (FTIR), and electrospray ionization/ion trap/mass spectrometry (ESI/ion trap/MS) were employed for characterization of HS. The portable RO system exhibited high yield and recovery of DOM for concentrating refinery effluent. The concentration of dissolved organic carbon (DOC) in the refinery effluent was 9.9mg/l, in which humic acids (HA) and fulvic acids (FA) accounted for 2.3% and 34.6%, respectively. Elemental and SUV(254) analyses indicated relative high amounts of aliphatic structures and low amounts of aromatic structures in refinery effluent-derived HS. Refinery effluent-derived HS displayed lower molecular weight than natural HS. The number-average molecular weight (M(n)) and the weight-average molecular weight (M(w)) of HA were 1069 and 2934, and those of FA were 679 and 1212 by SEC, respectively. By ESI/ion trap/MS, the M(n) and the M(w) of FA were 330 and 383. Four kinds of carbon structures (aliphatic, aromatic, heteroaliphatic, and carboxylic carbons) were found in refinery effluent-derived HS by (13)C NMR analysis. The quantitative results support the interpretation that these HS are rich in aliphatic carbons and poor in aromatic carbons. Proteinaceous materials were identified by FTIR analysis in refinery effluent-derived HS.

Environmental Monitoring↗

Electrokinetic fingerprinting of grafted polyelectrolyte layers--a theoretical approach.

Electrokinetic fingerprinting (EF) was introduced by Marlow and Rowell [Marlow BJ, Rowel RL. Langmuir 1990;6:1088] for the comprehensive characterization of charged particle surfaces. Afterwards, EF was applied by many groups for the characterization of "hard" (i.e. non-swelling) surfaces. However, the advantages of EF could not yet utilized for the characterization of grafted polyelectrolyte layers (PL) since the theoretical background was not yet elaborated. A theory for the characterization of PL at complete dissociation of the functional groups was developed by Ohshima [Adv Colloid Interface Sci 1995;62:189] and later extended by Dukhin et al. [Dukhin S, Zimmermann R, Werner C. J Colloid Interface Sci 2005;286:761] for any degree of dissociation. Further progress in the characterization of soft surfaces may be achieved by combining EF and surface conductivity (SC) measurements. Both theory and experiment demonstrate that integrated measurements of SC and apparent zeta potential zeta(a) in broad ranges of pH and ionic strength provide information about Donnan potential Psi(D), surface charge, pK and surface potential Psi(0), while the interpretation is more uncertain, when only zeta(a) is measured. This advanced method of PL characterization is established for PL grafted on flat surfaces. When PL are formed on spherical particles, the SC may be measured by means of conductometry and/or dielectric spectroscopy. However, the current theories can only be applied within a rather narrow range of the practically relevant conditions. To overcome this limitation, an unified approach to the theory of electrophoresis for spherical particles with grafted PL was elaborated taking into account the existence of two different electrokinetic models for soft surfaces. While one model is focused on hydrodynamic permeability of soft surface and disregards surface current, another model considers the surface current and disregards electrokinetic water transport within the soft surface layer. Unification became possible through generalization of the capillary osmosis theory over soft surfaces.

Electric Conductivity↗

90-day oral (gavage) study in rats with galactooligosaccharides syrup.

A 90-day oral (gavage) study was conducted in male and female Sprague Dawley rats to investigate the safety of Vivinal galactooligosaccharides (GOS) syrup at 2500 or 5000 mg/kg bw/day. A reference control containing fructooligosaccharides (FOS) was used to match the oligosaccharide and digestible sugars in the test material (approximately 45% and 30%, respectively) and to assess if these had an impact on food consumption. Measurements included clinical observations, body weights, food consumption, hematology, clotting parameters, blood chemistries, urinalysis, ophthalmologic examinations, gross necropsies, organ weights, and histological examinations. There were no effects of feeding GOS syrup at either concentration on any parameter except food consumption. Statistically significant decreases (7-13%) in food consumption were seen in both sexes in the GOS syrup-treated animals at 5000 mg/kg bw/day and animals treated with the FOS control when compared to the reverse osmosis deionized (RODI) water controls. Based on the lack of toxicological effects in the study, the NOAEL for Vivinal GOS syrup is 5000 mg/kg bw/day when administered by gavage for 90 consecutive days.

Administration, Oral↗