REGULATION OF THE PRIMING OF EXOCYTOSIS AND THE DISSOCIATION OF SNAP-25 AND VAMP-2 IN ADRENAL CHROMAFFIN CELLS

The MgATP-dependent priming step of exocytosis has been suggested to b e regulated negatively by GTP-binding protein G(o) in permeabilized ad renal chromaffin cells. We have reported that synaptosomal-associated protein of 25 kDa (SNAP-25) and vesicle-associated membrane protein 2 (VAMP-2) form a complex in chromaffin cells, and the complex dissociat es during MgATP-dependent priming. In this study, we examined whether G(o) controls such dissociation of the SNAP-25/VAMP-2 complex in the r egulation of priming. In digitonin-permeabilized cells, MgATP-gamma-S which can be a phosphate donor for protein phosphorylation failed to c ause priming and dissociation of the SNAP-25/VAMP-2 complex. Mastopara n, which directly activates G(o), selectively inhibited priming and bl ocked dissociation of the SNAP-25/VAMP-2 complex. These results sugges t that ATP hydrolysis and dissociation of the SNAP-25/VAMP-2 complex a re responsible for priming. These results also suggest that dissociati on of the complex is one of the sequential steps for priming controlle d by G(o). (C) 1997 Elsevier Science Ireland Ltd.