Field Effects in Experimental Bilayer Lipid Membranes and Biomembranes

Abstract

Interfaces are heterogeneous and as such they are usually electrified as a result of charge transfer, separation and/or redox reactions. In these aspects biomembranes are unique; they possess two interconnecting interfaces through which energy transfer and material exchange such as electronic charges and ions are possible. Further, owing to the chemical nature of lipids, biomembranes are generally negatively charged at physiological pH. These negative charges generate an electrostatic potential at the membrane-solution interface, which results in an electrical double layer at each side of the membrane. Therefore, the Guoy-Chapman theory of the diffuse double layer is frequently invoked to characterize the BLM system (Tien, 1974; Blank, 1986). Clearly, any disturbance of these electrical double layers such as ion concentration changes including H+, or absorption of electromagnetic radiation by the membrane, would reflect in a change in the potential difference across the system. This potential difference across the membrane may be transient or steady. Also, owing to their ultrathinness (<100 Å), very large field strengths in excess of 100,000 volt/cm can be developed across biomembranes under a small electrical potential differrence. Since biomembranes are complex, they are not amenable to simple analysis. Therefore, one approach is to obtain relevant observations on a sufficiently well-defined reconstituted membrane system. The interpretation of experimental results thus obtained would be much less ambiguous. It is along these lines of reasoning that we wish to discuss the effect of electric field in experimental bilayer lipid membranes (BLM and Liposomes) in relation to biomembranes.