SNAP-25 and synaptotagmin involvement in the final Ca(2+)-dependent triggering of neurotransmitter exocytosis.
In neurons, depolarization induces Ca2+ influx leading to fusion of synaptic vesicles docked at the active zone for neurotransmitter release. While a number of proteins have now been identified and postulated to participate in the assembly and subsequent disengagement of a vesicle docking complex for fusion, the mechanism that ultimately triggers neuroexocytosis remains elusive. Using a cell-free, lysed synaptosomal membrane preparation, we show that Ca2+ alone is sufficient to trigger secretion of glutamate and furthermore that Ca(2+)-signaled exocytosis is effectively blocked by antibodies and peptides to SNAP-25, a key constituent of the vesicle docking complex. In addition, Ca2+ inhibits the ability of synaptotagmin, a synaptic vesicle protein proposed as a calcium sensor and triggering device, to associate with this docking complex. These results support a model in which Ca(2+)-dependent triggering of neurotransmission at central synapses acts after ATP-dependent potentiation of the docking-fusion complex for membrane fusion.
Mehta
P P
PP
Department of Neuropharmacology, Scripps Research Institute, La Jolla, CA 92037, USA.
Battenberg
E
E
Wilson
M C
MC
D000255:Adenosine Triphosphate / Q000031:analogs & derivatives / Q000494:pharmacology; D000595:Amino Acid Sequence; D000818:Animals; D000906:Antibodies / Q000494:pharmacology; D000918:Antibody Specificity; D015153:Blotting, Western; D002118:Calcium / Q000494:pharmacology*; D002135:Calcium-Binding Proteins; D002413:Cations, Divalent / Q000494:pharmacology; D002540:Cerebral Cortex / Q000502:physiology*; D005089:Exocytosis / Q000187:drug effects / Q000502:physiology*; D018698:Glutamic Acid / Q000378:metabolism*; D007425:Intracellular Membranes / Q000187:drug effects / Q000502:physiology; D007700:Kinetics; D008562:Membrane Glycoproteins / Q000037:antagonists & inhibitors / Q000276:immunology / Q000502:physiology*; D008565:Membrane Proteins; D051379:Mice; D008969:Molecular Sequence Data; D009419:Nerve Tissue Proteins / Q000037:antagonists & inhibitors / Q000276:immunology / Q000502:physiology*; D010455:Peptides / Q000494:pharmacology*; D050825:Synaptosomal-Associated Protein 25; D013574:Synaptosomes / Q000187:drug effects / Q000502:physiology*; D050857:Synaptotagmins; D014357:Trypsin / Q000494:pharmacology
D000906:Antibodies; D002135:Calcium-Binding Proteins; D002413:Cations, Divalent; D008562:Membrane Glycoproteins; D008565:Membrane Proteins; D009419:Nerve Tissue Proteins; D010455:Peptides; C494209:Snap25 protein, mouse; D050825:Synaptosomal-Associated Protein 25; D050857:Synaptotagmins; C022571:adenosine 5'-O-(3-thiotriphosphate); D018698:Glutamic Acid; D000255:Adenosine Triphosphate; D014357:Trypsin; D002118:Calcium