NONLINEAR DC ELECTRICAL RESPONSE IN A BILAYER-LIPID MEMBRANE - EFFECTOF BATHING SOLUTIONS

The physical origin of a nonlinear electrical response in a bilayer li pid membrane (BLM) separating. two aqueous bathing solutions has been attributed by earlier workers to field induced pore formation in the l ipid moiety, which provides ionic pathways. Recently, we reported simi lar nonlinearity in the absence of any ion source, viz., in solid film s of lipids. The study ruled out the possibility of pore formation bei ng the only mechanism of transmembrane conductance. Using the BLM of o xidized cholesterol in n-decane, we report here our studies on the rol e of bathing soution on the I-V characteristics of these membranes. Th e nonlinearity is maintained in the presence pf an electron donor as w ell as an electron acceptor in the bathing solution, although there is a distinct difference in the nature of the nonlinearity in the two ca ses. Our results indicate that three factors, namely, pore formation, the semiconducting properties of the constituent lipid molecules, and the mechanism of transmembrane charge transport, are responsible for t he observed nonlinearity.