Abstract
In digitonin-permeabilized adrenal chromaffin cells, Ca 2+-induced catecholamine release can be resolved into at least two sequential steps: a MgATP-dependent priming step and a MgATP-independent Ca 2+-triggered step. Botulinum neurotoxins types A and E cleaved SNAP-25, and blocked MgATP-independent Ca 2+-induced catecholamine release from the permeabilized chromaffin cells. When the permeabilized cells were primed by pretreatment with MgATP, the amount of SNAP-25 associated with VAMP-2 decreased, and the fraction of SNAP-25 proteolyzed by the neurotoxins increased. These results suggest that dissociation of SNAP-25 and VAMP-2 occurs during the MgATP-dependent priming step, and SNAP-25 plays some important roles in the subsequent MgATP-independent step.
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