title: Modulation of an early step in the secretory machinery in hippocampal nerve terminals.
abstract: In hippocampal neurons, neurotransmitter release can be regulated by protein kinase A (PKA) through a direct action on the secretory machinery. To identify the site of PKA modulation, we have taken advantage of the ability of the neurotoxin Botulinum A to cleave the synaptic protein SNAP-25. Cleavage of this protein decreases the Ca2+ responsiveness of the secretory machinery by partially uncoupling Ca2+-sensing from fusion per se. This is expressed as a shift toward higher Ca2+ levels of the Ca2+ to neurotransmitter release relationship and as a perturbation of synaptic delay under conditions where secretion induced by the Ca2+-independent secretagogue ruthenium red is unimpaired. We find that SNAP-25 cleavage also perturbs PKA-dependent modulation of secretion; facilitation of ruthenium red-evoked neurotransmitter release by the adenylyl cyclase activator forskolin is blocked completely after Botulinum toxin A action. Together with our observation that forskolin modifies the Ca2+ to neurotransmitter release relationship, our results suggest that SNAP-25 acts as a functional linker between Ca2+ detection and fusion and that PKA modulates an early step in the secretory machinery related to calcium sensing to facilitate synaptic transmission.
authors.affiliation: Laboratory of Cellular Signaling, Department of Zoology and Genetics, Iowa State University, Ames, IA 50011, USA. Trudeal@ere.umontreal.ca
authors.forename: L E
authors.initials: LE
authors.lastname: Trudeau
authors.forename: Y
authors.initials: Y
authors.lastname: Fang
authors.forename: P G
authors.initials: PG
authors.lastname: Haydon
mesh_terms: D000818:Animals; D019274:Botulinum Toxins, Type A / Q000633:toxicity; D002118:Calcium / Q000502:physiology; D017868:Cyclic AMP-Dependent Protein Kinases / Q000502:physiology*; D004594:Electrophysiology; D006624:Hippocampus / Q000166:cytology / Q000502:physiology*; D008565:Membrane Proteins; D009419:Nerve Tissue Proteins / Q000502:physiology*; D009465:Neuromuscular Agents / Q000633:toxicity; D051381:Rats; D013569:Synapses / Q000502:physiology*; D009435:Synaptic Transmission / Q000187:drug effects / Q000502:physiology; D050825:Synaptosomal-Associated Protein 25
chemical_list: D008565:Membrane Proteins; D009419:Nerve Tissue Proteins; D009465:Neuromuscular Agents; C494210:Snap25 protein, rat; D050825:Synaptosomal-Associated Protein 25; D017868:Cyclic AMP-Dependent Protein Kinases; D019274:Botulinum Toxins, Type A; D002118:Calcium