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At least 433 records · Page 24Linked to original sources
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↗
PubMed2003

Computer-aided simulation and design of nanofiltration processes.

The modelling of membrane filtration processes is often performed by applying black-box models or short-cut methods, because of the complexity of the molecular interactions on and inside the membrane. The assumptions made for short-cut methods can be applied with accuracy to reverse osmosis processes, whereas the simulation of nanofiltration can lead to unreliable results that sometimes deviate from real conditions to a great extent. A steady-state process simulation, NF-PROJECT, based on input information from membrane characterization, was developed (isothermal operation). The individual separation characteristics of each membrane element are calculated in an iterative sequence, illustrating the successive reduction in permeability and rejection between the elements arranged inside the pressure vessel. The simulation provides information on the increasing feed concentration and osmotic pressure, the hydraulic pressure loss, the deterioration of the flow conditions in the vessel, and the joint performance of the membrane elements to be analyzed. Taking an example from a practical application, a two-stage nanofiltration pilot plant was simulated, the results of which are presented in this article. Examples of optimization potentials are illustrated for the target criteria of economic efficiency (specific energy costs), permeate quality, and flow.

Biotechnology↗
PubMedDate not supplied

Is ultraviolet radiation on haemodialysis RO water beneficial?

The quality of dialysis fluids has become increasingly important in the treatment of HD patients. Purified water represents over 95% of its volume. Bacterial and endotoxin content of Reverse Osmosis (RO) water is usually kept under control by bacterial filters, inserted in the distribution departure loop, and by monthly disinfection of the distribution circuit; the simpler the circuit, the better. This paper reports 12 years experience during which Ultraviolet Irradiation (UV) has replaced bacterial filters. To keep the bacterial growth under control in a complex RO water circuit (including a tank and multiple loops) a simple UV lamp was inserted in the departure line. It proved sufficient to keep bacterial count within AAMI norms. Failure of the UV lamp was associated with a rise of up to 500 cfu/ml in the last (fourth week) before routine disinfection. Normal levels were again obtained after replacement of the UV lamp. Six years later, a second UV lamp was added on the return loop. Bacterial counts and endotoxin levels in RO water promptly fell to <1 cfu/ml and <0.125 EU, till today. It is concluded that UV lamps should be favoured over bacterial filters in systems that are not disinfected daily, such as the RO water circuit. The principle of UV irradiation is explained and its advantage over bacterial filters is discussed. Future possible applications of UV are presented.

Colony Count, Microbial↗
PubMed1985

A central role for cell osmolarity in isotonic fluid transport across epithelia.

Previous theoretical models for solute-solvent coupling in epithelia that dealt only with the intercellular channel did not predict isotonic transport except when very high cell membrane permeabilities were assumed. To study this issue, we have developed the formalisms for osmotic equilibration at an alternative location, the apical cell membrane (including its adjacent unstirred layer), which are somewhat simpler than those for the channel. Much as in other models, we confirm that only rather unrealistically high values of the cell membrane permeability lead to isotonic transport. We have also found, however, that isotonic transport can occur at much lower values of the cell membrane permeability if the concentration within the cell differs slightly from that in the ambient medium. This emphasizes the importance of incorporating the intracellular concentration as an integral part to any transport model, such as in the present apical membrane version of local osmosis.

Animals↗
PubMed1966

Streaming potentials in the rat small intestine.

1. The effect of adverse osmotic pressure gradients on fluid transfer and electrical potential across the wall of sacs of rat everted small intestine was investigated.2. Addition of mannitol to the mucosal fluid produced a potential change of 0.062 mV/m-osM and a decrease in fluid transfer of 0.015 ml./m-osM/hr. This is consistent with the production of streaming potentials due to fluid movement through negatively charged pores in the intestine.3. The solute-linked fluid movement does not pass through these negatively charged pores which are responsible for the streaming potentials.4. From the magnitude and polarity of the streaming potential a value of -50 mV has been calculated for the zeta potential at the phase boundary in the pores.5. Streaming potentials have been used to measure the equivalent pore radius, and a value of 4A has been obtained.6. It is concluded that electro-osmosis is not responsible for fluid transfer by the intestine, and the potential difference associated with hexose transfer is not electrokinetic in origin.

Animals↗
PubMed1993

Convective fluid flow through the paracellular system of Necturus gall-bladder epithelium as revealed by dextran probes.

1. Bidirectional paracellular fluxes using radioactive dextrans as inert molecular probes have been measured across Necturus gall-bladder epithelium during conditions of normal fluid absorption. There is a net flux at all radii analysed (0.4-2.2 nm) in the direction of fluid absorption. 2. The net flux is substantial at all radii within the range. The data extraplate to 2 x 10(-6) cm s-1 at zero probe radius, which is very close to the rate of epithelial fluid absorption. 3. The unstirred layers at the epithelial faces during transport have been determined; their contribution to the net fluxes is negligible. 4. Two possible mechanisms for the net flow of probes are considered: (i) that the probes diffuse across the junctions and are then entrained in a local osmotic flow along the interspaces and subepithelium; (ii) that the probes are entrained in volume flow across the junctions and the emergent solution subsequently passes through the interspaces and subepithelium. Model calculations clearly rule out mechanism (i) in which the maximum net flow obtainable is less than 10% of that observed. In addition the presence of leak paths shunting the junctions is not compatible with the observed fluxes. With mechanism (ii) the net flows are correctly predicted with all the fluid flow being transjunctional. The fluid absorption is therefore entirely paracellular. 5. The slope of the net flow curve shows no apparent change in magnitude over the range of the probe radii, indicating that effectively only one population of convective channels is present with parallel walls separated by about 7.7 nm. This agrees with the width previously determined by electron microscopy. 6. If the fluid absorption is junctional then the cellular route offers little if any relative contribution. The hydraulic conductivity of the junctions is not high enough, or the osmotic permeability of the membranes low enough, to accommodate this by osmosis and therefore the junctional fluid absorption must be non-osmotic.

Absorption↗
PubMed1995

Outer hair cell length changes in an external electric field. II. The role of electrokinetic forces on the cell surface.

An isolated cochlear outer hair cell can elongate or shorten when electrically stimulated, as discovered by Brownell et al. [Science 227, 194-196 (1985)]. In their experiments, the cylindrically shaped cell was fixed at one end, and was positioned between two electrodes which lie on the cell axis, but were far from the cell (transcellular stimulation). A model is developed to predict the component of the cell's elongation which arises from only electrokinetic phenomena. Outside the cell, electro-osmosis produces a drag on the lateral wall which almost exactly balances the electrophoretic force. In contrast to previous theories, we find that the electrokinetic response is governed by the free end of the cell, not the lateral wall. If the surface charge density of the free end lies between -0.004 and -0.07 C/m2 (corresponding to the zeta potential between -5 and -60 mV), then our model predicts elongations that are comparable in magnitude to experimentally measured values.

Electric Stimulation↗
PubMed1970

Fluid transport: concentration of the intercellular compartment.

Intercellular spaces of Periplaneta rectal pads are visible at a magnification of x 100 and distend during fluid uptake. Samples (0.025 to 0.1 nanoliter) obtained by micropuncture from the spaces were consistently more concentrated than the fluid in the rectal lumen. This observation supports the hypothesis of "local" osmosis in epithelial fluid transport.

Animals↗
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↗
PubMed1984

Changes in bone histoquantitative parameters and histochemical staining reactions for aluminium in a group of patients with chronic renal failure following a reduction in the aluminium concentration of the haemodialysis fluid.

Bone biopsies from a group of 16 patients in chronic renal failure treated by intermittent haemodialysis were available for histoquantitative and histochemical assessment before and after the introduction of reverse osmosis treatment of the dialysis fluid. This treatment reduced the aluminium concentration of the fluid from 1.15 mg/l to less than 0.06 mg/l. After the changeover there was an increase in the extent of calcification fronts. Overall, there was a decrease in the histochemical staining reactions for aluminium, although a few cases showed increased reactions. A large percentage of cases showing decreased reactions also had decreased osteoid volumes. It is concluded that reduction of the concentration of aluminium in the dialysis fluid is associated with an improvement in mineralisation state, and this is further evidence of the importance of minimising the aluminium burden of patients with chronic renal failure.

Aluminum↗
PubMed1998

Routes and mechanism of fluid transport by epithelia.

The mechanism of fluid transport by leaky epithelia and the route taken by the transported fluid are in dispute. A consideration of current mathematical models for coupling of solutes and water, as well as the methodologies for the study of fluid transport, shows that local osmosis best accounts for water movement. Although it seems virtually certain that the tight junctions are water permeable, the fraction of absorbed fluid that crosses the tight junction cannot yet be determined with confidence.

Animals↗
PubMed2005

Mechanism of osmotic flow in a periodic fiber array.

The classic analysis by Anderson and Malone (Biophys J 14: 957-982, 1974) of the osmotic flow across membranes with long circular cylindrical pores is extended to a fiber matrix layer wherein the confining boundaries are the fibers themselves. The equivalent of the well-known result for the reflection coefficient sigma0 = (1 - phi)2, where phi is the partition coefficient, is derived for a periodic fiber array of hexagonally ordered core proteins. The boundary value problem for the potential energy function describing the solute distribution surrounding each fiber is solved by defining an equivalent fluid annulus in which the pressures and osmotic forces are determined. This model is of special interest in the osmotic flow of water across a capillary wall, where recent experimental studies suggest that the endothelial glycocalyx is a quasiperiodic fiber array that serves as the primary molecular sieve for plasma proteins. Results for the reflection coefficient are presented in terms of two dimensionless numbers, alpha = a/R and beta = b/R, where a and b are the solute and fiber radii, respectively, and R is the outer radius of the fluid annulus. In general, the results differ substantially from the classic expression for a circular pore because of the large difference in the shape of the boundary along which the osmotic force is generated. However, as in circular pore theory, one finds that the reflection coefficients for osmosis and filtration are the same.

Animals↗
PubMed1975

The bacteriological quality of hemodialysis solution as related to several environmental factors.

The bacterial concentrations of the municipal water increased by more than 39-fold when subjected to reverse osmosis; then decreased by greater than 200-fold within the reservoir and water supply system of the hemodialysis center. The bacterial concentrations of dialysate solutions in contact with proportioning single-pass artificial kidney machines were as low or lower than the water from the hemodialysis center system (less than 10 CFU/100 ml.). The complete opposite was observed in the recirculating single-pass artificial kidney machines where bacterial concentrations in the dialysate solution reached levels greater than 1.0 X 10(6) CFU/100 ml.

Bacillus↗
PubMed1996

Transepithelial water permeability in microperfused distal airways. Evidence for channel-mediated water transport.

Water movement across the airway epithelium is important for regulation of the volume and composition of airspace fluid. A novel approach is reported here to measure osmotic and diffusional water permeability in intact airways. Small airways (100-200 microns diameter, 1-2 mm length) from guinea pig lung were microdissected and perfused in vitro using concentric glass holding and perfusion pipettes. For measurement of osmotic water permeability (Pf), the airway lumen was perfused wit PBS (300 mOsM) containing a membrane impermeable fluorophore, fluorescein sulfonate (FS), and the airway was bathed in solutions of specified osmolalities. Pf determination was based on the changes in FS fluorescence at the distal end of the airway resulting from transepithelial water transport. Pf was 4-5 x 10(-3) cm/s at 23 degrees C and independent of lumen flow rate (10-100 nl/min) and the magnitude and direction of the osmotic gradient (bath osmolality 50-600 mOsM). Temperature dependence measurements gave an activation energy of 4.4 kcal/mol (15-37 degrees C). Pf was not altered by 0.3 mM HgCl2 or 50 microM forskolin, but was increased to 31 x 10(-3) cm/s by 100 micrograms/ml amphotericin B, indicating that osmosis is not limited by unstirred layers. Diffusional water permeability (Pd) was measured by H2O/D2O (deuterium oxide) exchange using the H2O/D2O-sensitive fluorescent probe aminonapthelane trisulfonic acid in the lumen. Measured Pd was 3-6 x 10(-6) cm/s at 23 degrees C, indicating significant restriction to water diffusion by unstirred layers. Antibody localization of water channels showed strong expression of the mercurial-insensitive water channel (AQP-4) at the basolateral membrane of airway epithelial cells. These results provide functional evidence that water movement across the distal airway epithelium is mediated by water channels.

Animals↗
PubMed1991

Terrestrial physical and chemical processes for liquid waste treatment.

Experiences gained from full-scale evaluation of advanced treatment processes used for reclaiming wastewaters should help in the evaluation of potential treatment systems for treatment and reuse of water in space. Water Factory 21 is a 0.66 m3 s-1 (15 million gallons per day) water reclamation plant in California that has been in operation since 1976. The plant receives biologically treated wastewater. Lime treatment is effective for removal of heavy metals. Volatile organic constitutes are efficiently removed by air stripping. Non-volatile organic constituents are removed by activated carbon adsorption and reverse osmosis (RO). RO is a highly effective polishing step, and removes most of the remaining materials including inorganic salts, heavy metals, and organics. RO removed 85% of the total organic carbon, down to about 1 mg l-1, which is lower than in many treated drinking waters. The series of treatment processes used insured virus and pathogen removal, with lime treatment and chlorination together proving highly effective. Sufficient data has been collected to provide statistically reliable confidence limits to be set on the performance of each unit process.

Cadmium↗
PubMed2005

TRPV4 exhibits a functional role in cell-volume regulation.

Tight regulation of the cell volume is important for the maintenance of cellular homeostasis. In a hypotonic environment, cells swell owing to osmosis. With many vertebrate cells, swelling is followed by an active reduction of volume, a process called regulatory volume decrease (RVD). A possible participant in RVD is the non-selective cation channel TRPV4, a member of the TRP superfamily that has been shown to react to hypotonic stimuli with a conductance for Ca2+. As a model for cell-volume regulation, we used a human keratinocyte cell line (HaCaT) that produces TRPV4 endogenously. When HaCaT cells were exposed to a hypotonic solution (200 mOsm) maximal swelling was followed by RVD. During swelling and volume regulation, a strong Ca2+ influx was measured. Gd3+, an inhibitor of TRPV4, blocked RVD of HaCaT cells and the accompanying rise of cytosolic Ca2+. To define the role of TRPV4 in volume regulation, a TRPV4-EGFP fusion protein was produced in CHO cells. CHO cells are unable to undergo RVD under hypotonic conditions and do not produce TRPV4 endogenously. Fluorescence imaging revealed that recombinant TRPV4 was localized to the cell membrane. Production of TRPV4 enabled CHO cells to undergo typical RVD after hypo-osmolarity-induced cell swelling. RVD of TRPV4-transfected CHO cells was significantly reduced by Gd3+ treatment or in Ca2+-free solution. Taken together, these results show a direct participation of TRPV4 in RVD.

Animals↗
PubMed1997

[Stimuli sensitive changes in electrical surface properties of soft membranes: from a synthesized polymer to a biological system].

The electrical surface properties of biological cells have been studied, which provided us with the fundamental knowledge about the cell surface. The change in shape or biological functions of cells may affect the surface properties and can be detected by electrokinetic measurements. Biological cell surfaces are covered with polysaccharide chains, some are charged and some are not. Some polysaccharides produce a hydrogel matrixes under a proper condition. We thus consider it reasonable that cell surface is approximated by a hydrogel surface. Electrophoretic mobility measurements are useful for studying the surface properties of biological cells suspended as colloidal particles in an electrolyte solution. The electro-osmotic velocity measurements on the other hand are advantageous to the study of the surface properties of slab-shaped biological systems such as membranes. This work was started with a hydrogel, as a model material. As a hydrogel, poly(N-isopropylacrylamide) poly(NIPAAm), abbreviated as hereafter, was chosen, because this hydrogel changes its volume depending on temperature. The dependence of the electrophoretic mobility of latex particles covered with poly(NIPAAm) hydrogel layer or of the electro-osmotic mobility on poly(NIPAAm) plate upon temperature and ionic strength of the dispersing medium was well explained with an electrophoretic mobility formula for "soft particles" developed by Ohshima. The electrokinetic measurements and the explanation of data with an electrophoretic mobility formula for "soft particles" give us information about the surface charge density and the "softness" of soft surfaces. On the basis of the findings with hydrogels, we have discussed the relationship between the changes in shape or function of the biological cells and the change in physicochemical surface properties using these measurements. To study the change in physicochemical properties of the cell surface caused by apoptosis, we have measured the electrophoretic mobilities of intact and apoptotic human promyelocytic leukemia cell lines, HL-60RG cells. We have also studied the differences observed in surface properties of malignant lymphosarcoma cell line, RAW117-P, and its variant, RAW117-H10, with a high metastatic property to the liver. In both cases, the cell surfaces became softer by the changes of biological functions. We have applied electrophoresis and electro-osmosis measurements to the study of the electrokinetic surface properties of rat basophilic leukemia cells, RBL cells. It was also found that the surface of Human umbilical vein endothelial cells, HUVEC, is considerably soft as compared with those of other biological cells we have studied before.

Acrylic Resins↗
PubMed2003

Volume kinetic analysis of fluid shifts accompanying intravenous infusions of glucose solution.

Volume kinetics is a mathematical tool for macroscopic (whole-body) evaluation of the distribution and elimination of fluid given by intravenous infusion. Although the kinetic system has mostly been applied to crystalloid fluids, such as Ringer's solution, it has more recently been extended to glucose solution, which is characterized by interdependence between glucose and fluid kinetics. The elimination of glucose, as estimated by a one-compartment open model, serves as the driving force for cellular uptake of glucose and, by virtue of osmosis, of water. Key findings include the observation that the infused fluid, besides being accumulated in the cells, occupies a central body fluid space (V1), which is no larger than 3-4 L, and that the cellular hydration has a much longer time-course than the hydration of V1. This explains the risk of hypovolemia associated with rapid infusion of 5% glucose; the dilution of V1, which is quite substantial owing to the small size of this space at baseline, stimulates a brisk diuresis while the excess water is being "trapped" in the cells along with the glucose. Model linearity has been demonstrated for 2.5% glucose solution and this allows the construction of nomograms for administration of such fluid during surgery and critical illness.

Body Fluid Compartments↗