RT Journal Article
SR Electronic
T1 Differential Regulation of Exocytosis by α- and β-SNAPs
JF The Journal of Neuroscience
JO J. Neurosci.
FD Society for Neuroscience
SP 53
OP 61
DO 10.1523/JNEUROSCI.22-01-00053.2002
VO 22
IS 1
A1 Xu, Jianhua
A1 Xu, Yimei
A1 Ellis-Davies, Graham C. R.
A1 Augustine, George J.
A1 Tse, Frederick W.
YR 2002
UL http://www.jneurosci.org/content/22/1/53.abstract
AB We examined the role of SNAPs, soluble proteins that attachN-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-SNAP, 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- and β-SNAP have different actions in exocytosis. Thus, the ratio of different isoforms of SNAPs can determine release probability at the levels of [Ca2+]ithat are involved in regulation of exocytosis.