Electrical conductivity in lipid bilayer membranes induced by pentachlorophenol

Abstract

Electrical conductivity induced in thin lipid bilayer membranes by pentachlorophenol has been studied. The membranes were formed from phosphatidyl choline, phosphatidyl ethanolamine, or phosphatidyl glycerol and various amounts of cholesterol. The position and the magnitude of the maximum of the conductivity vs. pH curve depend on the type of lipids and cholesterol content. At low pentachlorophenol concentrations and low pH the concentration dependence of conductivity is quadratic and becomes linear at higher pH. Above 10(-5) M of pentachlorophenol the concentration dependence of the membrane conductivity tends to saturate. Presence of pentachlorophenol enhances membrane transport of nonactin-K+ complex. Increase of cholesterol content increases pentachlorophenol induced conductivity in all membranes and shifts the conductivity toward lower pH. For phosphatidyl choline the largest rate of change of membrane conductivity with cholesterol occurs at 1:1 phospholipid to cholesterol molar ratio. Pentachlorophenol is found to be a class II uncoupler and the experimental results are consistent with the hypothesis that the membrane permeable species are dimers formed by combination of neutral and dissociated pentachlorophenol molecules. Several schemes of membrane conduction, including dimer formation in the aqueous phase as well as at the membrane-water interface have been considered. Arguments are given in favor of the formation of dimers within the membrane surface.