On the dynamics of the electric field induced breakdown in lipid membranes

Electric field methods are powerful tools for cell characterization and manipulation. Important biotechnological applications, e.g., electrofusion of cells or electroinjection of macromolecules into living cells, rely on membrane breakdown. Despite the widespread use of these techniques, the process of membrane breakdown is poorly understood: a better understanding can be expected to lead to higher efficiencies. The present study used planar lipid bilayers in order to limit the number of experimental parameters. Membrane rupture was induced by careful application of short electric field pulses: measurement of the subsequent increase in membrane conductivity with time permitted the underlying mechanism to be characterized. The initial process of pore formation starts a few μs after the onset of the pulse, and the ensuing breakdown of the entire lipid membrane occurs within about a millisecond (pore widening velocity of a few cm/s). The kinetics of the pore-opening process could be influenced qualitatively by adding surfactants and lipid-attached macromolecules, respectively. Changing the effective mass per unit area of membrane, which could be brought about by using known percentages of lipids with covalently bound, hydrophilic polymers, allowed a model for the pore widening process to be quantitatively tested.