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PubMed2001

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↗
PubMed1976

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↗
PubMed1998

Osmotic effects on volume and motility of bull sperm exposed to membrane permeable and nonpermeable agents.

Factorially arranged experiments were designed to study prefreeze packed cell volume (PCV) changes and associated percentages of motile and unstained bull sperm in simple macromolecule-free Tyrode's solution and egg yolk-Tris (EYT), varying in osmolarity, and with addition of rapidly permeating cryoprotectants, glycerol and 1,2-propanediol, and nonpermeating substances, sucrose and NaCl. The percentage of motile and unstained sperm was assessed after resuspending sperm in 300 mOsm/L Tyrode's solution. At 25 degreesC PCV increased in Tyrode's solution as osmolarity was decreased from 250 to 150 mOsm/L and decreased as Tyrode's solution was increased to 400 mosmol/L. The relationship of PCV to the reciprocal of the osmolarity was essentially linear over the range of 150 to 400 mOsm/L, but PCV did not decrease further in solutions ranging from 500 to 1000 mOsm/L. The percentage of motile sperm declined to zero in Tyrode's solution at 700 mOsm/L, but 40% of the sperm were still unstained in 1000 mOsm/L solutions. The addition of glycerol or 1,2-propanediol had little effect on PCV. With glycerol or 1,2-propanediol added to 308 mOsm/L Tyrode's solution to give a total of 1267 mOsm/L, there were 49 and 56% motile sperm, respectively, compared to 1% with NaCl added to give 787 mOsm/L. The PCV and percentage of motile sperm suspended in EYT responded to osmotic changes similar to those reported for Tyrode's solution at both 25 and 5 degreesC. Some sperm remained motile after initial exposure to 800 mOsm/L solutions. These findings may have application in improving bull sperm cryopreservation.

Animals↗
PubMed1988

Diffusive water permeability in isolated kidney proximal tubular cells: nature of the cellular water pathways.

The diffusive water permeability (Pd) of the plasma membrane of proximal kidney tubule cells was measured using a 1H-NMR technique. The values obtained for the exchange time (Tex) across the membrane were independent of the cytocrit and of the Mn2+ concentration (in the range 2.5 to 5 mM). At 25 degrees C the calculated Pd value was (per cm2 of outer surface area without taking into account membrane invaginations) 197 +/- 17 microns/sec. This value equals 22.3 +/- 1.9 microns/sec when the invaginations are taken into account. Cell exposure to 2.5 mM parachloromercuribenzenesulfonic acid, pCMBS, (for 20 to 35 min) reduced Pd to 45% of its control value. Five mM dithiothreitol, DTT, reverted this effect. The activation energy for the diffusive water flux was 5.2 +/- 1.0 kcal/mol under control conditions. It increased to 9.1 +/- 2.2 kcal/mol in the presence of 2.5 mM pCMBS. Using our previous values for the osmotic water permeability (Pos) in proximal straight tubular cells the Pos/Pd ratio equals 18 +/- 1, under control conditions, and 3.2 +/- 0.3 in the presence of pCMBS. These experimental results indicate the presence of pathways for water, formed by proteins, crossing these membranes, which are closed by pCMBS. Assuming laminar flow (within the pore), from Pos/Pd of 13 to 18 an unreasonably large pore radius of 12 to 15 A is calculated which would not hinder cell entry of known extracellular markers. Alternatively, for a single-file pore, 11 to 20 would be the number of water molecules which would be in tandem inside the pore.(ABSTRACT TRUNCATED AT 250 WORDS)

4-Chloromercuribenzenesulfonate↗
PubMed1987

Comparison of the effects of inserted C40- and C50-terminally dihydroxylated carotenoids on the mechanical properties of various phospholipid vesicles.

We have measured the extent of incorporation of zeaxanthin (C40) and decaprenozeaxanthin (C50) in unilamellar vesicles of dimyristoylphosphatidylcholine (n-C14) and dipalmitoylphosphatidylcholine (n-C16). The incorporation is larger when the molecular length of the carotenoid corresponds to the thickness of the phospholipid bilayer. Stereochemically pure 2,3-di-O-phytanyl-sn-glycero-1-phosphocholine was prepared by modification of the polar heads of the phospholipids of Halobacterium halobium. Vesicles of this branched-chain ether phospholipid incorporate poorly the carotenoids, whereas egg lecithin vesicles incorporate them better. Osmotic swelling and water permeability of vesicles, with or without carotenoids, were measured in a stopped-flow, light-scattering system. The reinforcing effect (lower permeability and higher rigidity) of carotenoids at 1.5 mol% incorporation into diphytanylphosphatidylcholine vesicles is comparable to that of 5 mol% cholesterol; however, carotenoids have no measurable effect on the egg lecithin vesicles. These results imply that the reinforcement of the membrane depends on a subtle adjustment of the phospholipid-carotenoid system.

1,2-Dipalmitoylphosphatidylcholine↗
PubMed2003

Extracellular lysines on the plasmodial surface anion channel involved in Na+ exclusion.

The human malaria parasite, Plasmodium falciparum, induces an unusual ion channel, the plasmodial surface anion channel (PSAC), on its host red blood cell (RBC) membrane. PSAC has a broad selectivity with permeability to anions, sugars, amino acids, purines, and certain vitamins, suggesting a role in nutrient acquisition by the intracellular parasite. Permeating solutes cover a range of molecular sizes and may be either neutral or carry a net negative or positive charge. Despite this broad selectivity, PSAC must efficiently exclude Na+ to avoid osmotic lysis of infected RBCs in the bloodstream. Here, we used amine-reactive N-hydroxysulfosuccinimide esters to probe PSAC's unusual selectivity. PSAC permeation rates, measured with both a kinetic osmotic lysis assay and single-channel patch-clamp, irreversibly decrease after treatment with these reagents. Sequential labelings with different esters and the effects of their chain length suggest that PSAC has multiple lysine residues near its extracellular pore mouth and that inhibition occurs via steric hindrance of its pore by the amide-linked side chain. When combined with the effects of pH on permeation, these findings implicate a combination of cation repulsion by pore mouth charges and a weak binding site for permeant solutes in PSAC's broad selectivity yet effective exclusion of Na+.

Animals↗
PubMed1998

High microvascular endothelial water permeability in mouse lung measured by a pleural surface fluorescence method.

Transport of water between the capillary and airspace compartments in lung encounters serial barriers: the alveolar epithelium, interstitium, and capillary endothelium. We previously reported a pleural surface fluorescence method to measure net capillary-to-airspace water transport. To measure the osmotic water permeability across the microvascular endothelial barrier in intact lung, the airspace was filled with a water-immiscible fluorocarbon. The capillaries were perfused via the pulmonary artery with solutions of specified osmolalites containing a high-molecular-weight fluorescent dextran. An increase in perfusate osmolality produced a prompt decrease in surface fluorescence due to dye dilution in the capillaries, followed by a slower return to initial fluorescence as capillary and lung interstitial osmolality equilibrate. A mathematical model was developed to determine the osmotic water permeability coefficient (Pf) of lung microvessels from the time course of pleural surface fluorescence. As predicted, the magnitude of the prompt change in surface fluorescence increased with decreased pulmonary artery perfusion rate and increased osmotic gradient size. With raffinose used to induce the osmotic gradient, Pf was 0.03 cm/s at 23 degrees C and was reduced 54% by 0.5 mM HgCl2. Temperature dependence measurements gave an Arrhenius activation energy (Ea) of 5.4 kcal/mol (12-37 degrees C). The apparent Pf induced by the smaller osmolytes mannitol and glycine was 0.021 and 0.011 cm/s (23 degrees C). Immunoblot analysis showed approximately 1.4 x 10(12) aquaporin-1 water channels/cm2 of capillary surface, which accounted quantitatively for the high Pf. These results establish a novel method for measuring osmotically driven water permeability across microvessels in intact lung. The high Pf, low Ea, and mercurial inhibition indicate the involvement of molecular water channels in water transport across the lung endothelium.

Animals↗
PubMed1983

Structural and functional response of toad urinary bladder to LiCl.

The physiological and morphological response of toad urinary bladder was examined during mucosal exposure of LiCl both with and without vasopressin (VP). With 20 or 100 mU/ml of VP in the serosal bath there was a decrease in Jv between the first and second VP stimulation in LiCl-treated bladders (VP20, -14 +/- 6%; VP100, -16 +/- 5%) that was not different from that observed without LiCl (VP20, -8 +/- 3%, P = NS). However, with 1 mU/ml of VP, a significant decrease in Jv was evident in LiCl-treated (-30 +/- 10%) versus control sacs (+6 +/- 8%; P less than 0.02). At all VP concentrations tested, a significant decrease in SCC and PD was observed between the first stimulation without LiCl and the second stimulation with LiCl. Both osmotic (Pf) and diffusional water permeability (Pd) were increased significantly with 11 mM LiCl only, while neither basal nor VP-stimulated urea permeability (Pu) was affected. Morphological changes paralleled the physiological alterations induced by LiCl. These data demonstrate that LiCl interferes with the osmotic response of the toad bladder to low concentrations of VP, and increases both Pf and Pd while leaving Pu unaffected. These findings coupled with the cell swelling and intracellular vacuolization suggest the presence of a defect in transepithelial water movement somewhere beyond the apical membrane of the granular cell exposed to LiCl.

Animals↗
PubMed1968

Effect of osmolality on the hydraulic permeability coefficient of red cells.

The osmotic water permeability coefficient, L(p), for human and dog red cells has been measured as a function of medium osmolality, and found to depend on the osmolality of the bathing medium. In the case of human red cells L(p) falls from 1.87 x 10(-11) cm(3)/dyne sec at 199 mOSM to 0.76 x 10(-11) cm(3)/dyne sec at 516 mOSM. A similar decrease was observed for dog red cells. Moreover, L(p) was independent of the direction of water movement and the nature of the solute used to provide the osmotic pressure gradient; it depended only on the final osmolality of the medium. Furthermore, L(p) was not affected by pH in the range of 6 to 8 nor by the presence of drugs such as valinomycin (1 x 10(-6)M) and tetrodotoxin (3.2 x 10(-6)M). The instantaneous nature of the response to changes in external osmolality suggests that the hydraulic conductivity of the membrane is controlled by a thin layer at the outer face of the membrane.

Animals↗
PubMed1971

The response of duck erythrocytes to nonhemolytic hypotonic media. Evidence for a volume-controlling mechanism.

Duck erythrocytes were incubated in hypotonic media at tonicities which do not produce hemolysis. The cells' response can be divided into two phases: an initial rapid phase of osmotic swelling and a second more prolonged phase (volume regulatory phase) in which the cells shrink until they approach their initial isotonic volume. Shrinkage associated with the volume regulatory phase is the consequence of a nearly isosmotic loss of KCl and water from the cell. The potassium loss results from a transient increase in K efflux. There is also a small reduction in Na permeability. Changes in cell size during the volume regulatory phase are not altered by 10(-4)M ouabain although this concentration of ouabain does change the cellular cation content. The over-all response of duck erythrocytes is considered as an example of "isosmotic intracellular regulation," a term used to describe a form of volume regulation common to euryhaline invertebrates which is achieved by adjusting the number of effective intracellular osmotic particles. The volume regulatory phase is discussed as the product of a membrane mechanism which is sensitive to some parameter associated with cell volume and is capable of regulating the loss of potassium from the cell. This mechanism is able to regulate cell size when the Na-K exchange, ouabain-inhibitable pump mechanism is blocked.

Animals↗
PubMed2002

Permeability characteristics and osmotic sensitivity of rhesus monkey (Macaca mulatta) oocytes.

BACKGROUND: Permeability characteristics and sensitivity to osmotic shock are principal parameters that are important to derive procedures for the successful cryopreservation of mammalian oocytes. METHODS AND RESULTS: The osmotically inactive volume of rhesus monkey oocytes was determined by measuring their volumes in the presence of hypertonic solutions of sucrose from 0.2 to 1.5 mol/l, compared with their volume in isotonic TALP-HEPES solution. Boyle-van't Hoff plots at infinite osmolality indicated that the non-osmotic volumes of immature and mature oocytes were 20 and 17% respectively. Osmotic responses of oocytes exposed to 1.0 mol/l solutions of glycerol, dimethylsulphoxide (DMSO) and ethylene glycol (EG) were determined. Rhesus monkey oocytes appeared to be less permeable to glycerol than to DMSO or to EG. Sensitivity of oocytes to osmotic shock was determined by exposing them to various solutions of EG (0.1 to 5.0 mol/l) and then abruptly diluting them into isotonic medium. Morphological survival, as measured by membrane integrity, of oocytes diluted out of EG depended significantly on the concentration of EG (P < 0.01). CONCLUSION: Determination of permeability characteristics and sensitivity to osmotic shock of rhesus oocytes will aid in the derivation of procedures for their cryopreservation.

Animals↗