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PubMed1964

WATER TRANSFER AND CELL STRUCTURE IN ISOLATED CRAYFISH MUSCLE FIBERS.

Changes in volume of crayfish single muscle fibers in response to changes in ionic or electrical conditions have been studied in conjunction with electrophysiological measurements and electron microscopic examinations. The occurrence of at least three mechanisms of water movements is revealed, two being processes which are superimposed on the normal osmotic water movement that results from a change in the concentration of solute in the medium. Differences between the time courses of the changes in volume and potential on changing K(i)/K(o) indicate that water may be distributed unequally for a time within compartments of the fiber. Electron micrographs reveal a selective accumulation of water at the periphery of the fiber under certain conditions. A correlation of H(2)O transfer with a change in membrane potential is apparent in crayfish muscle fibers and is probably due to electroosmotic effects. Electrokinetic water movements are produced whenever the membrane potential is changed to a considerable degree by changing the level of K and/or Cl in the medium, or by applying currents with an intracellular microelectrode. Depolarizations cause shrinkage. Hyperpolarizations or repolarizations cause swelling. The volume changes are independent of the occurrence or absence of swelling in the anion-permselective transverse tubular system. They indicate that the fiber membrane along the surface is heterogeneous, not only with respect to the signs of its fixed charge sites, but also with respect to the sizes and relative permselectivities of these charged channels.

Animals↗
PubMed2000

Aquaporin-4-containing astrocytes sustain a temperature- and mercury-insensitive swelling in vitro.

In order to understand the molecular mechanism underlying astroglial swelling, we studied primary astrocyte cultures from newborn mouse and analyzed them for expression of functional water channels. Immunocytochemical analysis of mouse brain confirms the presence of AQP4 location in astrocytic endfeet with a polarized pattern, as found in rat. Using Southern blot PCR and Western blot analysis, we demonstrate that primary astrocyte cultures from mouse express the AQP4 water channel at both the RNA and protein levels. Two polypeptides, of 30 kDa and 32 kDa, were identified in the astrocytes. Densitometric analysis demonstrates that the 32-kDa form represents 25% of the total AQP4 protein. Moreover, immunofluorescence experiments show strong surface membrane expression of AQP4 protein in cultured cells, even though the polarity of the expression is not maintained. Furthermore, functional studies indicate that cultured astrocytes manifest rapid and temperature-independent volume changes in response to osmotic gradients, in agreement with a channel-mediated water transport. Water movement was found to be HgCl(2) insensitive, suggesting AQP4 and AQP7 as putative water channels. Using Western blot and PCR experiments, we exclude the presence of AQP7 in astrocytes, indicating that only AQP4 is responsible for the rapid water movement. Altogether, the results indicate that primary astrocyte cultures are a valid cell model for further investigation of the molecular mechanism of water movement in the brain and its physiological regulation.

Animals↗
PubMedDate not supplied

Water diffusion and exchange as they influence contrast enhancement.

The contrast-enhanced magnetic resonance imaging (MRI) signal is rarely a direct measure of contrast concentration; rather it depends on the effect that the contrast agent has on the tissue water magnetization. To correctly interpret such studies, an understanding of the effects of water movement on the magnetic resonance (MR) signal is critical. In this review, we discuss how water diffusion within biological compartments and water exchange between these compartments affect MR signal enhancement and therefore our ability to extract physiologic information. The two primary ways by which contrast agents affect water magnetization are discussed: (1) direct relaxivity and (2) indirect susceptibility effects. For relaxivity agents, for which T1 effects usually dominate, the theory of relaxation enhancement is presented, along with a review of the relevant physiologic time constants for water movement affecting this relaxation enhancement. Experimental issues that impact accurate measurement of the relaxation enhancement are discussed. Finally, the impact of these effects on extracting physiologic information is presented. Susceptibility effects depend on the size and shape of the contrast agent, the size and shape of the compartment in which it resides, as well as the characteristics of the water movement through the resulting magnetic field inhomogeneity. Therefore, modeling of this effect is complex and is the subject of active study. However, since susceptibility effects can be much stronger than relaxivity effects in certain situations, they may be useful even without full quantitation.

Animals↗
PubMed1996

Effect of cholera toxin on glucose absorption and net movements of water and electrolytes in the intestinal loop of sheep.

This study was designed to evaluate the effect of cholera toxin on glucose absorption and net movement of water and electrolytes in the jejunal loop of sheep. Intraluminal perfusion was performed at the rate of 1 ml/min with isotonic 10 mM glucose solution. Osmolality was adjusted by adding NaCl, and the outflow solution was collected every 10 min. After a 30 min control period, cholera toxin was applied intraluminally for 30 min at doses of 30, 60, and 120 micrograms/loop. In the control period, water, sodium and chloride were absorbed, while potassium and bicarbonate were secreted. Cholera toxin reversed the net absorption of water, sodium and chloride to net secretions, and this secretory response to cholera toxin was dose-dependent. Bicarbonate secretion was stimulated dose-dependently by cholera toxin. Potassium secretion was also increased at all doses, though this response was not dose-dependent. The net glucose absorption was decreased dose-dependently by cholera toxin. In conclusion, these results indicate that cholera toxin stimulates water and electrolyte secretion, and inhibits glucose absorption in the jejunal loop of sheep.

Animals↗
PubMed1996

[Study of peritoneal water channel expression in rats].

Removal of excess fluid from patients with chronic renal failure is one of the major objectives of peritoneal dialysis (PD). Water movement from capillary to dialysate derives from the dialysate-to-capillary osmotic gradient across the peritoneum. To explain the mechanism of water movement driven by the osmotic gradient through the peritoneum, the notion of a water selective "ultra small pore" has been proposed. The purpose of this study was to investigate the involvement of peritoneal water channels in water movement across the peritoneum in PD. The abdominal cavity of male anesthetized rats was catheterized for administration of a series of artificial dialysates. Experimental PD was performed for 90-180 min with 25 ml of hyperosmotic dialysate generated by glucose (600 mOsm), sucrose (600 mOsm), and sodium (1800 mg/dl, 600 mOsm). Analysis of the sodium concentration and osmolality of dialysate during experimental PD showed mercurial sensitive water transport that was compatible with water channel-mediated water transport in the peritoneum. RT-PCR amplification with cDNAs constructed from peritoneal mRNA revealed the existence of both AQP1 (CHIP28) and AQP4 (MIWC) water channels in the peritoneum. PD with hyperosmotic dialysate did not affect the expression of peritoneal water channels. As a result of an in situ hybridization study to investigate the localization of the peritoneal water channels, it was found that both channels were expressed in the sub-mesothelial layer containing capillaries. The results obtained in this study suggest that peritoneal water channels might play a role in fluid removal during PD.

Animals↗
PubMedDate not supplied

Interbasin underflow between closed Altiplano basins in Chile.

Interbasin ground water movement of 200 to 240 L/sec occurs as underflow beneath a mountainous surface water divide separating the topographically higher Salar de Michincha from the topographically lower Salar de Coposa internally drained basins in the Altiplano of northern Chile. Salt-encrusted flats (salars) and saline lakes occur on the lowest parts of the basin floors and comprise the principal evaporative discharge areas for the basins. Because a surface water divide separates the basins, surface water drainage boundaries do not coincide with ground water drainage boundaries. In the region, interbasin ground water movement is usually not recognized, but occurs for selected basins, and at places is an important component of ground water budgets. With increasing development of water for mining industry and potential exportation of ground water from the Altiplano for use at coastal cities, demonstration and quantification of interbasin movement is important for assessment of sustainable ground water development in a region of extreme aridity. Recognition and quantification of interbasin ground water underflow will assist in management of ground water resources in the arid Chilean Altiplano environment.

Chile↗
PubMed1972

Temperature dependence of vasopressin action on the toad bladder.

Toad bladders were challenged with vasopressin at one temperature, fixed on the mucosa with 1% glutaraldehyde, and then subjected to an osmotic gradient at another temperature. Thus, the temperature dependence of vasopressin action on membrane permeability was distinguished from the temperature dependence of osmotic water flux. As the temperature was raised from 20 degrees to 38 degrees C, there was a substantial increase in the velocity of vasopressin action, but osmotic flux was hardly affected. In this range of temperature the apparent energy of activation for net water movement across the bladder amounted to only 1.2 kcal/mole, a value well below the activation energy for bulk water viscosity. It is suggested that osmotic water flux takes place through narrow, nonpolar channels in the membrane. When the temperature was raised from 4 degrees to 20 degrees C, both vasopressin action as well as osmotic water flux were markedly enhanced. Activation energies for net water movement were now 8.5 kcal/mole (4 degrees -9 degrees C) and 4.1 kcal/mole (9 degrees -20 degrees C), indicating that the components of the aqueous channel undergo conformational changes as the temperature is lowered from 20 degrees C. At 43 degrees C bladder reactivity to vasopressin was lost, and irreversible changes in selective permeability were observed. The apparent energy of activation for net water movement across the denatured membrane was 6.6 kcal/mole. Approximately 1 microosmol of NaCl was exchanged for 1 microl of H(2)O across the denatured membrane.

Animals↗
PubMed1976

Effective stimulus for the Xenopus laevis lateral-line hair-cell system.

An in vitro preparation of the lateral-line organ of the African clawed toad Xenopus laevis was used to evaluate the properties of the physiological stimuli which are most effective in evoking neural responses in this simple hair-cell system. Changes in the mean firing rate and the amount of modulation of the neural activity in the fibers innervating the hair cells were determined during the presentation of well-controlled pressure or water-movement stimuli in a specially designed chamber that prevented movement and deformation of the organ during stimulation. It was shown that the most effective stimulus for the preparation was a varying flow of fluid past the organ. Sinusoidally varying water movements over a frequency range of 1 to 100 Hz were effective in evoking neural responses at stimulus amplitudes less than 10 mu peak-to-peak; in addition, a small response to a constant-velocity flow was found. Since no movement or deformation of the organ was present during the water-movement stimuli, it was concluded that these aspects of normal physiological stimuli were not necessary to evoke neural responses. Finally, it was demonstrated that the preparation was sensitive to neither constant nor varying-pressure stimuli.

Action Potentials↗
PubMed2006

Dispersal strategies in sponge larvae: integrating the life history of larvae and the hydrologic component.

While known to be uniformly non-feeding, short-lived, and potentially short dispersing, sponge larvae display different behaviours (swimming ability and taxis). Our aim was to show whether sponge larvae with different behaviours exhibit different dispersal strategies under variable intensity of water movements. We first assessed the distribution of larvae of six taxa: Dictyoceratida spp., Dysidea avara, Crambe crambe, Phorbas tenacior, Scopalina lophyropoda, and Cliona viridis, collected through plankton sampling, and the abundance of the corresponding adult sponges across three hard bottom communities and a sandy bottom from a north-west Mediterranean rocky shore. We then tested adult-larvae couplings (abundance of larvae vs abundance of adults) under increasing levels of water movements (surge) to assess the importance of this environmental factor in driving differences in dispersal strategies. Adults of Dictyoceratida spp., D. avara, and P. tenacior were most abundant in semi-dark caves (SDC), C. crambe and C. viridis in communities of sciaphilic algae (SA), whereas the distribution of S. lophyropoda was extremely patchy, being present almost only in the SA community of one of the five stations studied. Larvae of Dictyoceratida spp. and P. tenacior were more abundant in the SDC, whereas D. avara and C. crambe were homogeneously distributed across the communities. The larvae of C. viridis were more abundant in the SA communities and the S. lophyropoda larvae were mostly present in one station and one community (SA). Increased water movement did not modify the adult-larvae coupling for Dictyoceratida spp., D. avara, and C. crambe, whereas it broke up the positive association for P. tenacior and to some extent S. lophyropoda. For C. viridis, possible variability in adult-larvae coupling was not tested because the larvae were collected on only one day under calm sea conditions. We confirm that efficient-swimming larvae with some cue response can actively counteract hydrodynamic forces and highlight the importance of both larval behaviour and environmental conditions in determining small-scale patterns of dispersal.

Animals↗
PubMed2001

Hydrodynamic trail-following in harbor seals (Phoca vitulina).

Marine mammals often forage in dark or turbid waters. Whereas dolphins use echolocation under such conditions, pinnipeds apparently lack this sensory ability. For seals hunting in the dark, one source of sensory information may consist of fish-generated water movements, which seals can detect with their highly sensitive whiskers. Water movements in the wake of fishes persist for several minutes. Here we show that blindfolded seals can use their whiskers to detect and accurately follow hydrodynamic trails generated by a miniature submarine. This shows that hydrodynamic information can be used for long-distance prey location.

Acoustics↗
PubMed2003

Water transporting properties of hepatocyte basolateral and canalicular plasma membrane domains.

Previous work from our laboratory supports an important role for aquaporins (AQPs), a family of water channel proteins, in bile secretion by hepatocytes. To further define the pathways and molecular mechanisms for water movement across hepatocytes, we directly assessed osmotic water permeability (Pf) and activation energy (Ea) in highly purified, rat hepatocytes basolateral membrane vesicles (BLMV) and canalicular membrane (CMV) vesicles by measuring scattered light intensity using stopped-flow spectrophotometry. The time course of scattered light for BLMV and CMV fit well to a single-exponential function. In BLMV, Pf was 108 +/- 4 mum.s-1 (25 degrees C) with an Ea of 7.7 kcal/mol; in CMV, Pf was 86 +/- 5 mum.s-1 (25 degrees C) with an Ea of 8.0 kcal/mol. The AQP blocker, dimethyl sulfoxide, significantly inhibited the Pf of both basolateral (81 +/- 4 mum.s-1; -25%) and canalicular (59 +/- 4 mum.s-1; -30%) membrane vesicles. When CMV were isolated from hepatocytes treated with dibutyryl cAMP, a double-exponential fit was needed, implying two functionally different vesicle populations; one population had Pf and Ea values similar to those of CMV from untreated hepatocytes, but the other population had a very high Pf (655 +/- 135 mum.s-1, 25 degrees C) and very low Ea (2.8 kcal/mol). Dimethyl sulfoxide completely inhibited the high Pf value in this second vesicle population. In contrast, Pf and Ea of BLMV were unaltered by cAMP treatment of hepatocytes. Our results are consistent with the presence of both lipid- and AQP-mediated pathways for basolateral and canalicular water movement across the hepatocyte plasma membrane barrier. Our data also suggest that the hepatocyte canalicular membrane domain is rate-limiting for transcellular water transport and that this domain becomes more permeable to water when hepatocytes are exposed to a choleretic agonist, presumably by insertion of AQP molecules. These data suggest a molecular mechanism for the efficient coupling of osmotically active solutes and water transport during canalicular bile formation.

Animals↗
PubMed1979

Absorption of inorganic phosphate in the human small intestine.

1. Intestinal phosphate absorption in human subjects was studied by the technique of triple lumen intestinal perfusion in vivo. 2. Ileal phosphate absorption increased as the intraluminal phosphate concentration was increased. 3. Ileal rates of phosphate absorption were lower at any given intraluminal phosphate concentration than previously described jejunal rates. Acidification of the ileal lumen did not increase phosphate absorption. 4. Phosphate absorption was shown in the jejunum to be dependent on the intraluminal sodium concentration. 5. Phosphate absorption in the human small intestine consists of at least two components, one directly proportional to water movement and the second apparently independent of water movement.

Adult↗
PubMed1997

Blood-brain barrier water permeability and brain osmolyte content during edema development.

OBJECTIVE: To determine mechanisms that limit changes in brain water content during acute edema development. METHODS: A controlled, laboratory investigation of the physiologic and biochemical correlates of osmotic edema was performed in rats. Hypoosmotic hyponatremia was induced by intraperitoneal injection of distilled water. Serum osmolality and electrolytes and regional blood-brain barrier water permeability. Surface area (P.S) product, osmolyte contents, and capillary size were determined during 120 minutes of hypoosmotic brain edema development. Cerebral water content predicted from these data using a mathematical model of brain water movements was compared with measured changes in brain water content. RESULTS: Fifteen minutes after distilled water injection, mean +/- SEM blood serum osmolality and sodium concentration decreased from 291 +/- 3 mOsm and 131 +/- 13 mmol/L to 267 +/- 3 mOsm and 102 +/- 9 mmol/L, respectively. Specific gravity of cerebral gray matter, cerebral white matter, and basal ganglia decreased throughout the hypoosmotic exposure period and, for gray and white matter, correlated with blood serum osmolality and sodium plus potassium content. Glutamate, but not glutamine, glycine, or taurine, decreased 120 minutes after water injection. The regional water P.S product decreased by 40% to 60% within 60 minutes of the water injection, while capillary diameters in gray and white matter were unchanged. Brain water movements calculated from the mathematical model correctly predicted actual brain water content only if the hydraulic conductivity of the blood-brain barrier was allowed to vary in proportion to the measured P.S product and the measured loss of brain osmolytes was incorporated into the formulation. CONCLUSIONS: During the first hours of hypoosmotic hyponatremia, changes in brain volume are limited by increased resistance to osmotic flux of water into the brain and reduction in the brain content of inorganic and, to a smaller degree, organic osmolytes.

Analysis of Variance↗
PubMed1983

Intracellular pH, transepithelial pH gradients, and ADH-induced water channels.

Urinary bladders of frogs were exposed to a transepithelial proton and osmotic gradient (serosal pH 8.1, Tris or bicarbonate buffer; mucosal pH 5.8, unbuffered) while the alkalinization rate of the mucosal bath and the net water movement were simultaneously monitored. It was observed that 1) the mucosal alkalinization rate was dependent on serosal pH and buffer; 2) oxytocin increased the mucosal alkalinization rate only when serosal bicarbonate was employed, whereas the net water movement augmented both when serosal bicarbonate or Tris buffers were used; 3) amiloride did not modify the mucosal alkalinization rate either before or after oxytocin; 4) the increases in the mucosal alkalinization rate and in the net water movement induced by oxytocin (serosal bicarbonate) were negatively correlated. In other experiments intracellular pH (pHi) was estimated with the DMO distribution technique with the following results. 1) Oxytocin increased the pHi when either serosal bicarbonate or Tris buffers was used and even in the presence of a low mucosal pH (Tris buffer, pH 5.8). 2) Important cellular acidification was observed when CO2 was bubbled (to pH 5.8), whereas the hydrosmotic response to 8-bromo-cAMP was clearly inhibited. These results indicate that cellular alkalinization could play a pivotal role in action of ADH, show that ADH can modify the transepithelial pH equilibrium mechanism, and suggest that intracellular pH regulation and water permeability control can be linked regulatory processes.

8-Bromo Cyclic Adenosine Monophosphate↗
PubMed2004

Movement and biological activity of drip-applied 1,3-dichloropropene and chloropicrin in raised mulched beds in the southeastern USA.

Movement and biological activity of 1,3-dichloropropene (1,3-D) and chloropicrin applied through drip irrigation in raised beds was investigated at three locations in the southeastern USA. Tests were conducted in fields with dense populations of nutsedge (Cyperus spp), with one location also having a high level of soil nematodes, both of which served as biological indicators of the distribution of effective concentrations of 1,3-D and chloropicrin. Objectives were (1) to gain a better understanding of 1,3-D and chloropicrin movement and the extent of biological activity outside of the wetted bed area, and (2) to examine the effect of application rate, application concentration and subsequent irrigation events on movement and activity of 1,3-D and chloropicrin. InLine, an emulsifiable concentrate containing 60.8% w/w 1,3-D and 33.3% w/w chloropicrin, was injected into polyethylene mulched beds through the drip tubes and water movement in the beds was visualized by adding a blue dye to the injection system. Gas concentrations of 1,3-D and chloropicrin in soil were measured using Gastec detection tubes at different positions relative to the drip tube at 1-4 days after InLine application. After one week, mulch was removed and nutsedge survival evaluated at different positions in the bed. High concentrations of 1,3-D and chloropicrin were measured at the bed center and midway between the bed center and the shoulder, but concentrations were low at the bed shoulder. Width of nutsedge control was significantly greater than width of water movement. Plant-parasitic nematodes were controlled over the entire bed width, but nutsedge re-emerged at the bed shoulders regardless of treatment. Higher application rates and concentrations of 1,3-D + chloropicrin resulted in higher fumigant concentrations in soil air. Irrigations subsequent to application reduced soil air concentrations of 1,3-D and chloropicrin and increased water movement, as did the use of two drip tubes instead of one. The data show that the pesticidal activity of 1,3-D + chloropicrin extends beyond the waterfront and indicate a significant degree of fumigant activity of emulsifiable 1,3-D + chloropicrin. However, unlike plant-parasitic nematodes, nutsedge could not be controlled over the entire bed width, regardless of rate, concentration and volume of water applied.

Agriculture↗
PubMed2006

Decreased aquaporin expression leads to increased resistance to apoptosis in hepatocellular carcinoma.

Cells undergoing apoptosis are characterized by decreased cell size due to changes in intracellular ion concentration and rapid, aquaporin (AQP)-dependent water movement out of the cell, events required for the activation of pro-apoptotic enzymes. The current study demonstrates AQP 8 and 9 expression is significantly decreased in hepatocellular carcinoma (HCC) versus normal liver. Isolation of hepatic tumor cells (H4IIE) and hepatocytes confirmed a lack of water movement across the H4IIE cell membrane via AQPs and identified an inherent resistance of H4IIE cells to apoptotic stimuli. In contrast, hepatocytes rapidly responded to osmotic challenge through AQP-dependent water movement and underwent cell death following apoptotic stimulation.

Animals↗
PubMed1992

Convective movement of Ca2+ across guinea pig gallbladder epithelium.

Recently, much interest has developed in biliary calcium because of its importance in the pathogenesis and composition of gallstones. While much progress has been made in understanding the thermodynamic factors that control biliary calcium concentrations, little is known about the kinetic factors that control the movement of calcium across the gallbladder epithelium. These studies measure guinea pig gallbladder epithelial permeability to Ca2+ during in vivo convective water movement across the membrane. Water movement, ranging from -15.2 (absorption) to 6.3 microliters.min-1.cm-2 (water entry), was induced by placing hypotonic, isotonic, and hypertonic solutions into the gallbladder lumen. Calcium movement was found to be directly and linearly related to water flow, indicating that Ca2+ moved with the convective water flow, presumably across paracellular channels. The slope of this relationship (0.602), representing the concentration of calcium in the fluid translocated across the gallbladder epithelium, was only about half that of plasma or luminal contents, indicating that calcium movement across the membrane was restricted. The mean sieving coefficient (1 - r) of guinea pig gallbladder, calculated from this slope, was approximately 0.5, indicating that the epithelium is only moderately permeable to Ca2+. The results suggest that intraluminal chelation of Ca2+ for the possible prevention and/or treatment of calcium-containing gallstones is a potentially feasible therapeutic modality.

Animals↗