Electrofusion: A biophysical modification of cell membrane and a mechanismin exocytosis

The molecular bases of the exocytosis process remain poorly known. Many pro teins have been recognized to play key roles in the machinery. Their functi ons are well characterized in the specificity of the docking processes. For ces involved in the merging of the two partners must take into account the physics of membrane interfaces. The target membrane and the vesicle are bot h electrically charged interfaces. Strong electrostatic fields are triggere d when they are brought in close neighborhood. These fields are high enough to induce an electropermeabilisation process. It is now well known that wh en applied on a cell, an external field induces a modulation of the transme mbrane potential difference. When high enough the transmembrane potential m ay induce a membrane destabilisation. This results in a free exchange of po lar molecules across well defined parts of the cell surface. Furthermore, w hen permeabilization is present on two cells, if those parts of the cell su rfaces are brought in close contact, membrane merging occurs spontaneously. Cell fusion results from this membrane coalescence. The similarity with wh at is taking place in exocytosis is striking. The present review describes the state-of-the-art in the knowledge on electrofusion. It is emphasized th at it results from electropermeabilisation and not from a direct effect of the external field. A local destabilisation of the vesicle membrane results from electrostatic interactions while keeping unaffected its viability. Su ch processes appear relevant for what takes place during exocytosis. (C) 20 00 Societe francaise de biochimie et biologie moleculaire / editions scient ifiques et medicales Elsevier SAS.