IMPAIRMENT OF SYNTAXIN BY BOTULINUM NEUROTOXIN C-1 OR ANTIBODIES INHIBITS ACETYLCHOLINE-RELEASE BUT NOT CA2+ CHANNEL ACTIVITY

The involvement of syntaxin, an omega-conotoxin-sensitive Ca2+ channel -associated protein, in acetylcholine release was studied at synapses formed between rat sympathetic neurons in culture. Transmission at the se synapses involved omega-conotoxin-sensitive Ca2+ channels because a dose-dependent inhibition was observed when omega-conotoxin was bath- applied. Confocal microscope examination of immunofluorescent staining showed that syntaxin had a similar distribution to synaptic vesicle-a ssociated membrane proteins, synaptophysin and vesicle-associated memb rane protein/synaptobrevin-2, indicating that syntaxin molecules are c oncentrated in the presynaptic terminals. Botulinum neurotoxin C-1 app lied extracellularly or intracellularly into presynaptic neurons block ed synaptic transmission. Introduction of a monoclonal antibody, or po lyclonal antibodies, to syntaxin into the presynaptic neuron depressed the evoked release of acetylcholine without affecting Ca2+ influx thr ough Ca2+ channels. These results suggest that syntaxin plays an impor tant role in release of neurotransmitter by a nerve impulse and that t his mechanism is downstream of Ca2+ influx.