Differential regulation of exocytosis by α- and β-SNAPs

Jianhua Xu, Yimei Xu, Graham C.R. Ellis-Davies, George J. Augustine, Frederick W. Tse

Research output: Contribution to journalArticlepeer-review

30 Scopus citations


We examined the role of SNAPs, soluble proteins that attach N-ethylmaleimide-sensitive factor (NSF), in regulating exocytosis in single rat adrenal chromaffin cells. Whole-cell dialysis of Ca2+-buffered solution or photolysis of caged-Ca2+ was used to manipulate cytosolic Ca2+ concentration ([Ca2+]i), whereas exocytosis was measured via carbon fiber amperometry or membrane capacitance. Buffering [Ca2+]i to ∼170 nM produced a mean rate of exocytosis of approximately one amperometric event per minute. Including α-SNAP (60 or 500 nM) in the intracellular solution dramatically increased the mean rate of exocytosis. The stimulatory action of α-SNAP requires ATP hydrolysis mediated via NSF, because this action was blocked by intracellular dialysis of ATP-γ-S (2 mM) and could not be mimicked by a mutant α-SNAP that does not stimulate the ATPase activity of NSF. This action of α-SNAP was significant only at [Ca2+]i between 100 and 300 nM and was not shared by β-SNAP (500 nM), suggesting that α-SNAP enhanced a component of exocytosis that is regulated by a high-affinity Ca2+ sensor. In cells dialyzed with both α- and β-SNAR the rate of exocytosis was smaller than that produced by α-SNAP alone, suggesting that α- and β-SNAP interact competitively. Although only α-SNAP stimulated exocytosis at [Ca2+]i between 100 and 300 nM, both α- and β-SNAP isoforms equally slowed the time-dependent rundown of the exocytic response. Our results indicate that α- andβ-SNAP have different actions in exocytosis. Thus, the ratio of different isoforms of SNAPs can determine release probability at the levels of [Ca2+]i that are involved in regulation of exocytosis.

Original languageEnglish (US)
Pages (from-to)53-61
Number of pages9
JournalJournal of Neuroscience
Issue number1
StatePublished - Jan 1 2002
Externally publishedYes


  • Amperometry
  • Caged-calcium
  • Calcium dependence
  • Catecholamine release
  • Chromaffin cell
  • Flash photolysis
  • SNAREs
  • Whole-cell dialysis

ASJC Scopus subject areas

  • General Neuroscience


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