The Journal of Membrane Biology

Saito, Toshikazu; Essig, A.

doi: 10.1007/BF01868217pmid: 4201709

It has been demonstrated previously that aldosterone increases the electrical conductance of the toad bladder in association with the stimulation of active sodium transport. In the present study the concurrent measurement of electrical quantities and ion tracer flux distinguishes effects on active and passive pathways. Lack of an effect on passive Na+ or Cl− tracer flux in hemibladders preselected to eliminate large artefactual leaks indicates that aldosterone has no influence on physiological passive conductance. Thus, the enhancement of electrical conductance is entirely attributable to the active pathway. The magnitude of the increase in the active conductance was estimated. The data permitted also the comparison of effects on the flux ratio of Na+ at short circuit (f 0) and the electrical potential difference adequate to abolish active sodium transport (E Na). Even in membranes with minimal leakage the flux ratio does not reliably reflectE Na. Aldosterone increased meanf 0 from 11 to 22, but did not affectE Na.

Gruber, W.; Deuticke, B.

doi: 10.1007/BF01868218pmid: 4752450

Magnitude and characteristics of phosphate transfer through the erythrocyte membranes of ten mammalian species were measured using tracer exchange techniques. Remarkable quantitative species differences could be demonstrated, permeabilities (at an extracellular phosphate concentration of 10mM) increasing from 0.2×10−8 cm/sec (sheep) to 2.2×10−8 cm/sec (rabbit) in the sequence sheep <ox<cat<horse<pig<man<dog<guinea pig<rat<rabbit. In contrast, the characteristics of the phosphate transfer system, such as temperature depedency, dependency on anion composition and pH of the media and sensitivity to amphiphilic inhibitors proved to be very similar in all species, suggestive of a uniform mechanism of transfer. The quantitative differences in permeability which roughly parallel those reported for a number of nonelectrolytes could be correlated with the phosphatidylcholine and sphingomyeline contents of the membranes. The possible molecular basis of a causal relationship between phosphate permeability and phospholipid patterns is discussed.

Starzak, Michael

doi: 10.1007/BF01868219pmid: 4752451

The flux of permeant species through a membrane is examined using discrete state stochastic models for the transport process within the membrane. While a membrane flux is maintained due to a concentration gradient between bathing solutions, the distribution of species within the membrane evolves to a time invariant configuration which can differ significantly from the equilibrium configuration. Some special properties of these stationary states are examined using linear, microcanonical models for the membrane transport process. Analysis of these models reveals properties which are masked by the phenomenological analysis of irreversible thermodynamics. For example, the models can be used to study the nature of multi-state relaxation within the membrane by observation of the time dependence of the net membrane flux when the membrane is perturbed from its stationary state distribution. Under some conditions, multi-state models will produce relaxation similar to that observed for single-state processes. The symmetry within the membrane is a critical factor for monitoring relaxation processes within the membrane. Because of the stationary nature of the membrane configuration, statistical thermodynamic variables can be defined for the membrane configuration. The total system is not in equilibrium since the baths must still be described by dissipation functions. In the stationary state, the configurational entropy of the membrane is lowered relative to equilibrium and is shown to depend quadratically on the time independent parameter (j/p) wherej is the membrane flux andp is a characteristic transition probability for intra-membrane transitions. The basic membrane system serves as a quantitative example of the entropy reduction possible in a stationary state system. An allosteric transition mediated by the stationary state configuration is examined as a means of utilizing this negentropy production.

Hax, W.; Venrooij, G.; Denier van der Gon, J.; Elbers, P.

doi: 10.1007/BF01868220pmid: 4796219

Incubation of the free living soil amoebaAcanthamoeba castellanii with lysolecithins results in aggregation of the cells into multicellular masses. The cells in these masses form close junctions and are electrically coupled.

Zutphen, H.; Cornwell, David

doi: 10.1007/BF01868221pmid: 4796220

Hydrogen peroxide generated from dissolved oxygen through the alloxandialuric acid cycle affected both the permeability and the stability of lipid bilayer membranes. The permeability of the artificial membranes varied directly with the hydrogen peroxide concentration. Membrane stability varied inversely with the hydrogen peroxide concentration. Bilayers formed from solutions containing both phospholipid and the antioxidant vitamin E were less permeable and more stable in the presence of hydrogen peroxide than bilayers generated from solutions containing phospholipid alone. Peroxidation of phospholipid monolayers caused first an expansion of the films presumably through the introduction of peroxide groups. Further oxidation of phospholipid monolayers led to contraction of the films presumably through the formation of water-soluble products. The results of the monolayer studies and a consideration of the possible kinetics for the peroxidation reaction sequence have been used to explain the changes in the permeability and the stability of lipid bilayer membranes. Our data suggest that oxidation of lipid in biological membranes may first increase membrane permeability and then decrease membrane stability.

Couturier, E.; Bruno, O.; Metzger, P.; Leclercq, R.; Copinschi, G.

doi: 10.1007/BF01868222pmid: 4752452

Isolated rat mesentery, mounted in a diffusion cell, is used as a model for the study of vascular endothelium permeability characteristics. The passage of tracer molecules is measured in the absence of osmotic or hydrostatic pressure gradients across the mesentery. The permeability coefficient of the membrane for cortisol and progesterone is similar. When bound to transcortin, cortisol crosses mesentery at a significantly slower rate. Metyrapone diatartrate increases by 30% the passage of free and of transcortinbound cortisol, but is without effect on the passage of progesterone or glucose in the same conditions. When the transfer of cholesterol across mesentery is studied, a high percentage of the tracer is trapped by the membrane.

Steinberg, Malcolm; Armstrong, Peter; Granger, R.

doi: 10.1007/BF01868223pmid: 4205052

A sensitive method for assaying aggregation of dissociated cells has been developed which allows the determination of the mean number of cells per aggregate of a cell population. We have demonstrated that exposure of dissociated 6- or 7-day chick embryo neural retinal cells to trypsin in calcium-free solution renders them unable to aggregate for a half hour in stirred cell suspensions. Aggregation was noticeable first at 30 to 40 minutes and, progressed to the formation of massive compact aggregates. Because the half-hour aggregation lag occurred both in the absence of serum and in medium reclaimed from aggregated preparations, the possibilities were excluded that it was due either to an inhibitor of aggregation in the serum, or was the time required for release into the medium of soluble aggregation-promoting materials emanating from the cells themselves. Cells dissociated by divalent cation withdrawal (Ca++, Mg++-free saline with EDTA) aggregated without a lag. The trypsin-induced lag does not appear to be the result of trypsin adsorbed to the, surfaces of dissociated cells, as the lag is not abolished by addition of trypsin inhibitors to the aggregation medium. Microelectrophoresis of dissociated cells did not reveal changes in surface charge density during recovery from trypsinization. A variety of proteins and calcium ion, if present during trypsinization, protect the cells against the trypsin-induced aggregation lag. If the temperature was reduced from 37 to 6°C, aggregation of fully adhesive cell populations came to a complete halt within 2 to 3 minutes. Aggregation resumed with a 5 to 10 minute delay when the temperature was returned to 37°C. The rapidity of onset and reversal of inhibition of aggregation by low temperature treatment militates against the hypothesis that the low-temperature inhibition of aggregation acts by suppressing the synthesis of cell surface components necessary for adhesion. The abolition of the aggregation lag in trypsinized cells was also shown to be temperature-dependent; a 20-minute cold, pulse administered in the middle of the lag period extended the length of the lag by exactly 20 minutes.

Barbarese, E.; Sauerwein, H.; Simpkins, H.

doi: 10.1007/BF01868224pmid: 4360397

Erythroblasts from marrows of chicks infected with RNA-virus (strain Rerythroblastosis virus) were found to possess a small but consistent increase in the number of concanavalin A binding sites per cell compared to erythroblasts derived from the marrows of phenylhydrazine-treated birds. Both types of erythroblast possessed more surface glycoproteins per cell accessible to concanavalin A (Con A) than marrow and peripheral blood erythrocytes. Employment of concanavalin A conjugated to ferritin showed marked differences in the spatial arrangement of the Con A receptors between phenylhydrazine and virus-induced erythroblasts but little difference was observed in the surface density of the Con A sites between erythrocytes and erythroblasts, a result which agrees with the amount of bound labeled Con A when this data is expressed in terms of the cell surface.

Cremaschi, D.; Smith, M.; Wooding, F.

doi: 10.1007/BF01868225pmid: 4778804

The temperature dependence of fluid transport acrossin vitro preparations of goldfish gallbladder was measured using a gravimetric technique. Fluid transport showed a direct dependence on incubation temperature when the adaptation temperature was kept constant. For constant incubation temperature, transport fell as the adaptation temperature rose. The width of intercellular channels varied with incubation and adaptation temperature as expected if fluid were to cross the tissue by this route. The structure of the gallbladder was otherwise unaffected by changes of temperature. Intracellular concentrations of Na, K and Cl also depended on the environmental temperature of the fish. The levels of Na and Cl increased and the level of K decreased, at constant incubation temperature, as the adaptation temperature rose from 8 to 30°C. These changes took two to three weeks to become apparent while fluid transport regulated within 20 hours of raising the environmental temperature. The osmotic permeability of the gallbladder remained independent of both incubation and adaptation temperature.

Beaugé, L.; Ortiz, Olga

doi: 10.1007/BF01868226pmid: 4778805

Unidirectional as well as net sodium fluxes were studied in rat red blood cells incubated in potassium-free sodium and sodium-substituted solutions. In the absence of ouabain the magnitude of sodium efflux in different solutions followed the sequence Na>choline>tris>Mg; in the presence of 10−4 M ouabain the sequence was choline>tris>Na>Mg. In a sodium-magnesium mixture the ouabain-sensitive sodium influx as a function of the external sodium concentration followed more or less an S-shaped curve; at high external sodium there was good agreement with the efflux values, but below 90mM-Na all efflux points were above the influx ones. Both ouabain-insensitive Na influx and efflux were stimulated by external Na following a linear relationship though with different slopes. In net flux experiments these cells were able to extrude sodium against an electrochemical gradient in K-free ouabain Na−Mg and Na-choline mixture solutions. In K-free-Na-free magnesium media the ouabain-sensitive sodium loss increased proportionally to the square of the internal sodium, whereas the ouabaininsensitive loss went to saturation. In K-free sodium solutions the net Na gain was reduced as internal Na increased and was unaffected by ouabain. These results, plus the changes in the sodium influx/net Na gain ratio and in the rate constant for Na efflux when internal Na was modified, are consistent with the existence of a facilitated diffusion system for sodium movements which contributes, together with leakage, to the net Na gain in K-free sodium solutions.