in vitro binding of synaptic vesicles to the synaptic plasma membrane: Lack of effect of β-bungarotoxin

To help characterize the mechanisms of neurotransmitter release, and the role of the specific neurotoxin β-bungarotoxin in inhibiting release, the interaction of synaptic vesicles with the synaptic plasma membrane was investigated using two in vitro systems. Binding of radiolabeled synaptic vesicles to immobilized synaptic plasma membrane was specific, protein-dependent, and modulated by phosphorylation of membrane proteins. Stimulation of phosphorylation by phorbol ester increased binding, and reduction of phosphorylation by alkaline phosphatase or staurosporine reduced binding. β-Bungarotoxin did not alter basal binding of synaptic vesicles to synaptic plasma membrane, nor did it affect the increase in binding induced by phorbol esters. Under conditions which stimulate acetylcholine release from synaptosomes, both phorbol ester and 4-aminopyridine caused an increase in attachment of the synaptic vesicle marker protein synaptophysin to the synaptic plasma membrane. β-Bungarotoxin did not alter the change in localization of synaptophysin induced by either drug, under conditions in which it inhibits ACh release induced by 4-aminopyridine. It is concluded that β-bungarotoxin inhibition probably does not occur at the level of the interaction of the synaptic vesicle and the synaptic plasma membrane, but occurs at an earlier stage in the neurotransmission process.