title: Translocation of synapsin I in response to depolarization of isolated nerve terminals.
abstract: Depolarization of isolated nerve terminals (synaptosomes) has been shown to stimulate neurotransmitter release and to increase the phosphorylation state of a number of proteins, including synapsin I, in a Ca2+-dependent manner. Synapsin I, a prominent nerve terminal phosphoprotein, interacts with the cytoplasmic surface of small synaptic vesicles and with cytoskeletal elements in a phosphorylation-dependent manner. In the present study we have found that depolarization of synaptosomes resulted in a rapid (2-5 sec) translocation of synapsin I from the particulate to the cytosolic (soluble) fraction. This translocation of synapsin I correlated with its phosphorylation state and was dependent on the presence of Ca2+ in the incubation medium. The stoichiometry of phosphorylation of soluble synapsin I was considerably higher than that of synapsin I in the particulate fraction, under both basal and depolarizing conditions. These data are consistent with the hypothesis that, in situ, the phosphorylation of synapsin I promotes its translocation from synaptic vesicles/cytoskeleton to the cytosol. This phosphorylation/translocation may be instrumental in regulating the release of neurotransmitter.
authors.affiliation: Laboratory of Molecular and Cellular Neuroscience, Rockefeller University, New York, NY 10021.
authors.forename: T S
authors.initials: TS
authors.lastname: Sihra
authors.forename: J K
authors.initials: JK
authors.lastname: Wang
authors.forename: F S
authors.initials: FS
authors.lastname: Gorelick
authors.forename: P
authors.initials: P
authors.lastname: Greengard
mesh_terms: D000818:Animals; D002118:Calcium / Q000494:pharmacology; D002540:Cerebral Cortex / Q000502:physiology*; D005576:Colforsin / Q000494:pharmacology; D003600:Cytosol / Q000378:metabolism; D007700:Kinetics; D008564:Membrane Potentials; D009419:Nerve Tissue Proteins / Q000302:isolation & purification / Q000378:metabolism*; D010750:Phosphoproteins / Q000378:metabolism*; D010766:Phosphorylation; D051381:Rats; D016704:Synapsins; D013574:Synaptosomes / Q000187:drug effects / Q000502:physiology*
chemical_list: D009419:Nerve Tissue Proteins; D010750:Phosphoproteins; D016704:Synapsins; D005576:Colforsin; D002118:Calcium