KINETIC MECHANISMS OF MEMBRANE-FUSION MEDIATED BY ELECTRIC-FIELDS

External electric fields can induce the fusion of a wide variety of cell and artificial membranes. This experimental observation is a demonstration of an inherent ability of membranes to fuse if appropriate conditions are provided, and indicates the existence of properties of membrane systems, related to fusion, which are largely independent of the type of membrane. An approach to understanding more clearly the fundamental properties of membranes needed for fusion involves the comparison of systems of different levels of complexity, such as lipid monolayers, bilayers and plasma cell membranes. In all of these systems the physicochemical properties, especially viscosity, of the interacting membranes and the liquid layer between them are critical for the fusion kinetics. Other critical phenomenological parameters are the strength and duration of the electric pulse, which drives the fusion reaction. The fusogenic pulse induces a state of high Gibbs energy which leads to the destabilization of the membranes and the liquid layer between them by stochastic processes of growth of fluctuational waves and the overcoming of energy barriers. This results in the formation of localized molecular contacts, fusion junctions and pores, which may subsequently expand. Although this major kinetic pathway can be generally understood in terms of phenomenological models, the molecular mechanisms of electrofusion are unclear because of a lack of direct experimental measurements of the structural rearrangements during membrane merging. The elucidation of electrofusion mechanisms may provide clues to the understanding of the fundamental mechanisms of fusion in biological systems.