Phospholipid head group dipoles and electropore formation

Abstract

Classical electropermeabilization is the result of the delivery of electric field pulses on cells. The field pulse lasts from submicro to several milliseconds. The field intensity is large enough to induce a dramatic structural local alteration of the cell membrane organization. This results in an enhanced permeabilization of the target cell membrane. This is indeed a complex process and its molecular characterization remains an intense field of investigations. A membrane is a complex assembly where the polar head region is a charged system. It appears as a target of the field effect. A description of the lipid bilayer organization points out its role in the function of membrane. Interfacial water appears as a key component in the structural organization of the phospholipid head groups. A feedback between polar head dipoles and water dipoles results in a specific organization. Different biophysical approaches were developed to investigate the behavior of the phospholipid head group dipoles during and after the pulse delivery. The experiments were performed on membrane lipid models as well as on cell membranes under reversible electropermeabilization, where the cell viability is preserved through a resealing active process. The external field pulse affects the mean orientation of the head group dipoles and alters the local water content and self-organization. This is a key step in the induction of defects in electropermeabilization and their associated properties.