Interactions of presynaptic Ca2+ channels and snare proteins in neurotransmitter release.
N- and P/Q-type Ca2+ channels are localized in high density in presynaptic nerve terminals and are crucial elements in neuronal excitation-secretion coupling. In addition to mediating Ca2+ entry to initiate transmitter release, they are thought to interact directly with proteins of the synaptic vesicle docking/fusion machinery. These Ca2+ channels can be purified from brain as a complex with SNARE proteins, which are involved in exocytosis. In addition, N-type and P/Q-type Ca2+ channels are colocalized with syntaxin in high-density clusters in nerve terminals. The synaptic protein interaction (synprint) sites in the intracellular loop II-III (LII-III) of both alpha 1B and alpha 1A subunits of N-type and P/Q-type Ca2+ channels bind to syntaxin, SNAP-25, and synaptotagmin. Ca2+ has a biphasic effect on the interactions of N-type Ca2+ channels with SNARE complexes, stimulating optimal binding in the range of 10-30 microM. PKC or CaM KII phosphorylation of the N-type synprint peptide inhibits interactions with SNARE complexes containing syntaxin and SNAP-25. Introduction of the synprint peptides into presynaptic superior cervical ganglion neurons reversibly inhibits EPSPs from synchronous transmitter release by 42%. At physiological Ca2+ concentrations, synprint peptides significantly reduce transmitter release in injected frog neuromuscular junctions in cell culture, consistent with detachment of 70% of the docked vesicles from Ca2+ channels as analyzed by a theoretical model. Together, these studies suggest that presynaptic Ca2+ channels not only provide the Ca2+ signal required by the exocytotic machinery, but also contain structural elements that are integral to vesicle docking, priming, and fusion processes.
Department of Pharmacology, University of Washington, Seattle 98195-7280, USA.
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Catterall
D000818:Animals; D001001:Anura; D001921:Brain / Q000378:metabolism; D002118:Calcium / Q000378:metabolism; D015220:Calcium Channels / Q000235:genetics / Q000378:metabolism*; D003001:Cloning, Molecular; D008565:Membrane Proteins / Q000378:metabolism*; D008958:Models, Molecular; D009419:Nerve Tissue Proteins / Q000378:metabolism*; D009469:Neuromuscular Junction / Q000378:metabolism; D018377:Neurotransmitter Agents / Q000378:metabolism*; D010446:Peptide Fragments / Q000494:pharmacology; D010766:Phosphorylation; D050765:Qa-SNARE Proteins; D050600:SNARE Proteins; D009435:Synaptic Transmission; D033921:Vesicular Transport Proteins
D015220:Calcium Channels; D008565:Membrane Proteins; D009419:Nerve Tissue Proteins; D018377:Neurotransmitter Agents; D010446:Peptide Fragments; D050765:Qa-SNARE Proteins; D050600:SNARE Proteins; D033921:Vesicular Transport Proteins; D002118:Calcium