Abstract
Experiments on neuromuscular preparations from the frog Rana ridibunda assessed the effects of oxidation of membrane cholesterol on the presynaptic vesicle cycle. Application of cholesterol oxidase (1 activity unit) for 30 min oxidized about 0.007 mg of cholesterol per g of preparation and decreased the stability of lipid rafts in nerve terminals. Electrophysiological studies demonstrated that oxidation of cholesterol decreased evoked transmitter release. Experiments using fluorescent FM dyes demonstrated suppression of synaptic vesicle exo- and endocytosis processes, along with dispersal of clusters of synaptic vesicles. Comparative analysis of electrophysiological and optical data, along with experiments using a dye quencher, demonstrated that transmitter could be released from some synaptic vesicles through transient fusion pores (the kiss-and-run mechanism). It is suggested that oxidation of cholesterol suppresses evoked exocytosis and delivery of synaptic vesicles of the reserve pool to the exocytosis site, thus interfering with their clustering. Vesicles of the recycling pool release transmitter by the “kiss-and-run” mechanism.
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