Transport and separation of Ag(+) and Zn(2+) by donnan dialysis through a monovalent cation selective membrane.

Donnan Dialysis of Ag(+) and Zn(2+) was investigated through a cation exchange membrane (CMS Neosepta) when a proton concentration difference was maintained between the two sides of the membrane. Developed for the production of brine from sea water, CMS Neosepta showed a higher permeability to monovalent than to bivalent cations. Several physico-chemical parameters have been determined (electrical resistance, membrane potential, sorption of electrolytes, Zn(2+) and Ag(+) diffusion coefficients).

Potential study of basement membrane.

The membrane potential of a basement membrane (bovine-anterior-lens-capsule) was studied by use of the Gibbs-Donnan systems. The T.M.

Analysis of the ion transfer through the channel of 9,11,13,15-phenylalanylgramicidin A.

The behavior of an analogue of gramicidin A in which all four tryptophanyl residues are substituted by phenylalanyl and which shows a strong voltage effect on the single channel conductance is analyzed on the basis of a 'three-barrier--two-site' model. It is shown that in the gramicidin family the side chains of some amino acids, in spite of their location, which point outside the channel can play a major role in the binding of ions in the channel and thus can significantly modify the energy profile of the channel.

Transport of potassium ions across planar lipid membranes by the antibiotic, grisorixin: I. The equilibrium state and self-diffusion K+ fluxes.

42K+ tracer flux and steady-state conductance measurements were carried out with bilayer lipid membranes containing grisorixin, a carboxylic polyether antibiotic. When the membranes are placed between two bulk aqueous solutions of identical composition, the exchange or self-diffusion transmembrane flux of potassium is measured by a method which allows the characterization of the bilayer K+ permeability at the equilibrium state. The K+ self-diffusion flux increases with the pH in the range pH 6 to pH 9 and reaches a constant value for values above 9.

Transport of mercury compounds across bimolecular lipid membranes: effect of lipid composition, pH and chloride concentration.

The use of bimolecular lipid membranes (BLM) as model membrane allows the analysis of the transport of mercury compounds across the lipidic barriers of biological membranes. The results of flux measurements show that two mercury compounds--HgCl2 and CH3HgCl--cross the BLM but the overall permeabilities are dependent on the pH of the aqueous media, and are not apparently influenced by the different phospholipid constituents of the bilayers. On the other hand, electrical measurements show that, function of the chemical speciation, the transport of this metal is done essentially in the neutral form.

Ca2+-gramicidin A interactions and blocking effects on the ionic channel.

From spectroscopic data (infrared, CD and 13C-NMR) it is shown that Ca2+ interacts with gramicidin A and that a head-to-head gramicidin A dimer can have two Ca2+-binding sites located near the COOH termini. On the basis of this result, we can propose an explanation for the blocking effect of Ca2+ on the transport of alkali metal ions (Cs+ and K+) through gramicidin channels. The binding of Ca2+ is competitive with the alkali metal ion binding; Ca2+ cannot cross the gramicidin channel and its binding in the channel is voltage dependent.

Brain proteolipids. Isolation, purification and effect on ionic permeability of membranes.

Proteolipid apoproteins have been isolated from a whole bovine brain homogenate by chloroform/methanol extraction, and fractionated by chromatography on modified (lipophilic) Sephadex, followed by ion-exchange chromatography on CM-Trisacryl. The various final, highly hydrophobic, fractions are homogeneous (sodium dodecyl sulfate/polyacrylamide gel electrophoresis). Transmembrane ion transfers were studied by 22Na + flux and electrical conductance measurements.

Voltage and time dependence of the conductance of planar lipid bilayers doped with colicin A.

Voltage jump studies of planar bilayers doped with colicin A revealed two classes of time and voltage dependent conductance induced by colicin A. The first type of conductance, asymmetrically voltage dependent, measured as a time dependent process, was in agreement with previously described conductances of bilayers doped with colicin A or colicin E1. The second class of conductance appeared as a voltage dependent instantaneous conductance.

Transport of Na+ by monensin across bimolecular lipid membranes.

Transmembrane 22Na fluxes across bimolecular lipid membranes are measured under two different experimental conditions: (a) the pH is the same in the two bulk aqueous solutions on either side of the membrane while the concentrations of Na+ are different; (b) the concentration of Na+ are identical but pH of the two solutions are different. In this latter case, the transport of Na+ occurs in the opposite direction to the difference of the proton concentration. In both cases, the electrical charge flux in negligible.

Transmembrane electrical potential of excitable membranes: a pore analysis influence of surface charges and surface dipoles.

A treatment is proposed in order to establish the general expression of the zero-current transmembrane potential of excitable membranes. The membrane model considered here is that of a hydrocarbon layer which is impermeable to ions and which represents the lipid bilayer matrix. In this matrix are incorporated ionic channels.

Photocurrent response of bacteriorhodopsin adsorbed on bimolecular lipid membranes.

The photo response of bacteriorhodopsin adsorbed on a bimolecular lipid membrane has been investigated using short-circuit current measurements. The results revealed a biphasic current vs. time curve for the photocurrent at pH values of approx.

The influence of pH on the conductance of lipid bimolecular membranes in relation to the alkaline ion transport induced by carboxylic carriers grisorixin, alborixin and monensin.

The influence of the pH on the stability and stoichiometry of the complexes formed by carboxylic-antibiotics such as grisorixin, alborixin and monensin with alkaline and alkaline earth cations has been investigated. The maximum values of bimolecular lipid membrane conductance are obtained with grisorixin and potassium ion. The conductance-pH curves show a very pronounced maximum in the neutral pH range.

The transport of calcium and sodium ions across bilayers induced by neutral synthetic ligands used in specific electrodes.

Neutral synthetic ligands of calcium and sodium which enter into the liquid membrane composition of the selective electrodes of these ions have been incorporated within the bilayer. The membrane conductance measured shows that each of these two ligands behave as ion carriers for calcium or sodium ions. The selectivities with respect to the other alcaline or alcaline earth ions are similar to those observed by potentiometric measurements with thick liquid membrane selective electrodes.

Non-mediated zero voltage conductance of hydrophobic ions through bilayer lipid membranes.

A charge pulse technique applied to the study of charge transfer at metal-solution interfaces has been used to determine the capacity and the conductance of a membrane bilayer at both zero time and zero voltage. The transport of hydrophobic ions across a glycerol-monooleate bilayer (tetraphenyl borate, picrate, dipicrylamine and tetraphenyl arsonium) has been investigated by this method. A theoretical approach to the problem has been proposed based on one analogous to that used for the compact double layer at metallic electrodes.