IN-VITRO BINDING OF SYNAPTIC VESICLES TO THE SYNAPTIC PLASMA-MEMBRANE- LACK OF EFFECT OF BETA-BUNGAROTOXIN

To help characterize the mechanisms of neurotransmitter release, and t he role of the specific neurotoxin beta-bungarotoxin in inhibiting rel ease, the interaction of synaptic vesicles with the synaptic plasma me mbrane was investigated using two in vitro systems. Binding of radiola beled synaptic vesicles to immobilized synaptic plasma membrane was sp ecific, protein-dependent, and modulated by phosphorylation of membran e proteins. Stimulation of phosphorylation by phorbol ester increased binding, and reduction of phosphorylation by alkaline phosphatase or s taurosporine reduced binding. beta-Bungarotoxin did not alter basal bi nding of synaptic vesicles to synaptic plasma membrane, nor did it aff ect the increase in binding induced by phorbol esters. Under condition s which stimulate acetylcholine release from synaptosomes, both phorbo l ester and 4-aminopyridine caused an increase in attachment of the sy naptic vesicle marker protein synaptophysin to the synaptic plasma mem brane. beta-Bungarotoxin did not alter the change in localization of s ynaptophysin induced by either drug, under conditions in which it inhi bits ACh release induced by 4-aminopyridine. It is concluded that beta -bungarotoxin inhibition probably does not occur at the level of the i nteraction of the synaptic vesicle and the synaptic plasma membrane, b ut occurs at an earlier stage in the neurotransmission process.