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.

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.