We have used stage-specific assays for MgATP-dependent priming and for Ca(2+)-activated triggering in the absence of free MgATP to examine the effects of alpha-SNAP, 14-3-3 proteins and calmodulin on regulated exocytosis in permeabilized adrenal chromaffin cells. All three proteins lead to a Ca(2+)-dependent increase in catecholamine secretion. Both alpha-SNAP and 14-3-3 proteins stimulated in a priming but not in a triggering assay. In contrast, calmodulin was stimulatory in triggering but not priming. The effects of alpha-SNAP and 14-3-3 proteins were likely to be due to distinct mechanisms of action since they differed in Ca(2+)-dependency, time course and extent of stimulation and their effects were additive. alpha-SNAP and 14-3-3 proteins did not appear to exert their priming action through changes in synthesis of phosphatidylinositol (4,5) bisphosphate. The data show that these three proteins have distinct stage-specific actions on exocytosis and indicate that alpha-SNAP acts in an early MgATP-requiring stage and not in the late Ca(2+)-triggered steps immediately prior to membrane fusion as previously suggested.
Distinct effects of alpha-SNAP, 14-3-3 proteins, and calmodulin on priming and triggering of regulated exocytosis.
L H Chamberlain, D Roth, A Morgan, R D Burgoyne; Distinct effects of alpha-SNAP, 14-3-3 proteins, and calmodulin on priming and triggering of regulated exocytosis.. J Cell Biol 1 September 1995; 130 (5): 1063–1070. doi: https://doi.org/10.1083/jcb.130.5.1063
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