Two modes of exocytosis from synaptosomes are differentially regulated by protein phosphatase types 2A and 2B.
The inhibitors okadaic acid (OA), fostriecin (FOS) and cyclosporin A (CsA), were used to investigate the roles of protein phosphatases in regulating exocytosis in rat brain synaptosomes by measuring glutamate release and the release of the styryl dye FM 2-10. Depolarization was induced by 30 mM KCl, or 0.3 mM or 1 mM 4-aminopyridine (4AP). OA and FOS produced a similar partial inhibition of KCl- and 0.3 mM 4AP- evoked exocytosis in both assays, but had little effect upon exocytosis evoked by 1 mM 4AP. In contrast, CsA had no effect upon KCl- and 0.3 mM 4AP-evoked exocytosis, but significantly enhanced glutamate release but not FM 2-10 dye release evoked by 1 mM 4AP. None of the phosphatase inhibitors changed calcium signals from FURA-2-loaded synaptosomes either before or after depolarization. Pretreatment with 100 nM phorbol 12-myristate 13-acetate abolished the inhibitory effect of OA on exocytosis induced by 0.3 mM 4AP. Taken together, these results show that exocytosis from synaptosomes has a phosphatase-sensitive and phosphatase-insensitive component, and that there are two modes of phosphatase-sensitive exocytosis that can be elicited by different depolarization conditions. Moreover, these two modes are differentially sensitive to phosphatase 2A and 2B.
Baldwin
Monique L
ML
School of Biomedical Sciences, University of Newcastle and Clinical Neuroscience Program, Hunter Medical Research Institute, Callaghan, New South Wales, Australia.
Rostas
John A P
JA
Sim
Alistair T R
AT
D000818:Animals; D001923:Brain Chemistry; D019703:Calcineurin / Q000737:chemistry* / Q000378:metabolism; D065095:Calcineurin Inhibitors; D002118:Calcium / Q000032:analysis / Q000378:metabolism; D016572:Cyclosporine / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005089:Exocytosis / Q000187:drug effects / Q000502:physiology*; D005456:Fluorescent Dyes / Q000737:chemistry; D018698:Glutamic Acid / Q000378:metabolism; D010749:Phosphoprotein Phosphatases / Q000037:antagonists & inhibitors / Q000737:chemistry* / Q000378:metabolism; D054648:Protein Phosphatase 2; D051381:Rats; D013574:Synaptosomes / Q000737:chemistry / Q000187:drug effects / Q000201:enzymology*
D065095:Calcineurin Inhibitors; D004791:Enzyme Inhibitors; D005456:Fluorescent Dyes; D018698:Glutamic Acid; D016572:Cyclosporine; D019703:Calcineurin; D010749:Phosphoprotein Phosphatases; D054648:Protein Phosphatase 2; D002118:Calcium