Fusion of biomembranes by macroscopic electric fields

Abstract

Three events seem crucial for the fusion of biomembranes: the vesicles* become con- centrated, they then aggregate, and finally their membranes are destabilized. At physiological pH the membranes of most vesicles carry a net negative charge. Elec- trophoresis could be used to concentrate vesicles near a positive electrode, but then mutual electrostatic repulsion would pre- clude aggregation. H. A. Pohl pointed out that through a different electric mechanism, called 'dielectrophoresis'l neutral, but polarizable vesicles can be concentrated and even aggregated to form chains. In a homogeneous electric field a vesicle with- out net charge will become polarized, i.e. within the cell, negative charge accumu- lates at the side closest to the positive elec- trode and vice versa. Because of the net neutrality of the vesicle and the homogeneity of the electric field, the two charges will sense opposite forces that are equal in magnitude and hence cancel out. Consequently, in a homogeneous electric field only vesicles with a net charge will move (ordinary electrophoresis). How- ever, when the electric field is inhomogeneous, the forces exerted on the positive and the negative sides of the vesicle will differ, resulting in dielectrophoresis, i.e. movement towards higher