Rapid transbilayer phospholipid redistribution associated with exocytotic release of neurotransmitters from cholinergic nerve terminals isolated from electric ray Narke japonica.

Asymmetric phospholipid distribution between the outer and inner monolayers of cholinergic synaptosomal membranes at rest and their redistribution upon depolarization-induced acetylcholine (ACh) release were investigated. Translocation of phospholipids between the monolayers was measured using fluorescence-labeled phospholipid probes, NBD-PS, NBD-PE, and NBD-PC. The percentage of probes in the inner leaflet at equilibrium in synaptosomes at rest was estimated to be 63% (NBD-PS), 36% (NBD-PE), and 31% (NBD-PC). Depolarization-induced exocytosis induced rapid redistribution of these probes. Approximately 35% of PS and PC in the inner leaflet moved to the outer leaflet, whereas only 16% of PE moved. To further elucidate the mechanism of exocytosis and membrane fusion at presynaptic nerve terminals in the future, the rapid phospholipid translocation associated with exocytosis must be taken into account.