Presynaptic vesicles, exocytosis, membrane fusion and basic physical forces

Abstract

The theoretical hypothesis is presented trying to explain the vesicle release from presynaptic nerve ending and membrane fusion. This theoretical concept implies only essential physical forces such as electrostatic force and surface tension force. Transmembrane resting potential of approximately –70 to –80 mV means that the intracellular fluid is electronegative in comparison with extracellular one. In this concept it is supposed that the inner and outer lipid layer of the membrane also have different electrostatic charges. Presynaptic vesicles are made from cell membrane by endocytic process through which the vesicle loses the contact with cell membrane. Also, during the endocytic process, the inner lipid layer of the cell membrane becomes the outer lipid layer of presynaptic vesicle and vice versa. During the resting phase, equally charged lipid layers of presynaptic vesicle and cell membrane repel each other, but during the action potential, differently charged lipid layers strongly attract each other, bringing the presynaptic vesicle and cell membrane in close contact. Immediately thereafter, the surface tension forces open the pore and fuse both membranes trying to minimize the area of the contact between water fluids (extra and intracellular fluid) and lipid fluids (lipid membrane bilayer). Since only fundamental physical forces are involved in this process, it could be very fast, effective and almost inexhaustible. Similar mechanisms could be responsible for all exocytic processes and all membrane fusion processes in the cells.