ALTERATION OF CA2+ DEPENDENCE OF NEUROTRANSMITTER RELEASE BY DISRUPTION OF CA2+ CHANNEL SYNTAXIN INTERACTION/

Presynaptic N-type calcium channels interact with syntaxin and synapto some-associated protein of 25 kDa (SNAP-25) through a binding site in the intracellular loop connecting domains II and III of the alpha(1) s ubunit. This binding region was loaded into embryonic spinal neurons o f Xenopus by early blastomere injection. After culturing, synaptic tra nsmission of peptide-loaded and control cells was compared by measurin g postsynaptic responses under different external Ca2+ concentrations. The relative transmitter release of injected neurons was reduced by s imilar to 25% at physiological Ca2+ concentration, whereas injection o f the corresponding region of the L-type Ca2+ channel had virtually no effect. When applied to a theoretical model, these results imply that 70% of the formerly linked vesicles have been uncoupled after action of the peptide. Our data suggest that severing the physical interactio n between presynaptic calcium channels and synaptic proteins will not prevent synaptic transmission at this synapse but will make it less ef ficient by shifting its Ca2+ dependence to higher values.