Cholesterol and lipid rafts in the plasma membrane of nerve terminal and membrane of synaptic vesicles

Abstract

In this study, using neuromusclar preparations of frog cutaneous pectoris muscle and mouse diaphragm we have shown that the membranes of nerve terminals (NT) contain nearly two times more cholesterol than the plasma membrane of muscle fibers. Using the fluorescent B subunit of cholera toxin (CT-B), we identified the areas in the NT membranes with high concentrations of GM1 ganglioside, the marker molecule for cholesterol- and sphingolipid-enriched membrane microdomains, so-called lipid rafts. Intense fluorescent spots appear in the NT when lipid rafts were identified during high-frequency stimulation, which cause massive exocytosis of synaptic vesicles followed by endocytosis. The double staining of neuromusclar preparations with CT-B and FM1-43, a dye that is taken up into synaptic vesicles during endocytosis, has demonstrated good colabeling by these dyes. This indicates the presence of large amounts of cholesterol and lipid rafts in membranes of synaptic vesicles. Thus, cholesterol is present in NT membranes at the high concentration required for the organization of lipid rafts, which are common in the plasma membranes of the NT and the membranes of synaptic vesicles. The role of cholesterol and lipid rafts in the processes of exo- and endocytosis is discussed.