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.

Electrical conductivity, transfer of hydrogen ions in lipid bilayer membranes and uncoupling effect induced by pentachlorobenzenethiol (Pentachlorothiophenol)

“…The results obtained with PCP in the membraneforming solution were found not to be different from those with PCP in the bathing medium, as reported earlier [25]. For given concentrations of uncoupler the conductance of PCP membranes was always found to be smaller, typically by about one order of magnitude, than those treated with PCBT.…”

“…Slow transient currents, indicative of the development of diffusion polarization regime [19] were observed when the voltage bias across the membrane was changed. Such electrical response supports the hypothesis that the charge transfer across the membrane is accompanied by the diffusion of protons in the immediate vicinity of the membrane [3,20,25]. In order to provide some insight into the relationship between the molecular structure and the effect of the compound on membrane conductivity, we performed similar experiments with PCP, by incorporating PCP in the membrane-forming solution.…”

“…Both are known to be uncouplers of oxidative phosphorylation [32][33][34]36]. PCP is a commonly used pesticide that has been extensively studied [13,21,22,25,26,[32][33][34]. We have found, for example, that the onset of toxic effect due to PCP measured by the rate of carbon assimilation by an alga, occurs in parallel with the decrease of membrane electrical resistance [9].…”

How do protons cross the membrane-solution interface? Kinetic studies on bilayer membranes exposed to the protonophore S-13 (5-chloro-3-tert-butyl-2′-chloro-4′ nitrosalicylanilide)

“…We obtain a good fit to the data at all [NaC1] if the adsorption coefficient, flA, the only adjustable parameter, is taken to be 3 • 10 -2 cm. The strong adsorption of S-13 to bilayer membranes is charac- teristic of other weak acid protonophores [5,6,9,29,47]. The deviations from the theoretical curves noted at high concentrations of S-13 in the 0.1 M NaC1 solutions are presumably due to the production of electrostatic boundary potentials within the membrane, as discussed in detail elsewhere [5].…”

Physical effects of 3-phenylindole on ion transport across bilayer lipid membranes

“…Andreoli and Monahan (1968) found that fi1ipin caused extreme membrane instability while nystatin and amphotericin 8 decreased the electrical resistance of the membranes by as much as six orders of magnitude. Finkelstein and Cass (1968) demonstrated that the membranes became slightly anion selective in the presence of the polyenes and that increasing temperature greatly Smejtek, Hsu and Perman, 1976). Lea andCroghan (1969) and, independently, Finkelstein (1970) proposed a carrier model for the tl~ansport in which the uncoupler anion combines with a hydrogen ion at the membrane/aqueous interface, crosses the membrane in the form of a dimer, and releases the hydrogen ion at the opposite interface, resulting in a net proton flux.…”