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Synaptotagmin-7 is a principal Ca2+ sensor for Ca2+-induced glucagon exocytosis in pancreas
Article first published online: 13 MAR 2009
© 2009 The Authors. Journal compilation © 2009 The Physiological Society
The Journal of Physiology
Volume 587, Issue 6, pages 1169–1178, March 2009
How to Cite
Gustavsson, N., Wei, S.-H., Hoang, D. N., Lao, Y., Zhang, Q., Radda, G. K., Rorsman, P., Südhof, T. C. and Han, W. (2009), Synaptotagmin-7 is a principal Ca2+ sensor for Ca2+-induced glucagon exocytosis in pancreas. The Journal of Physiology, 587: 1169–1178. doi: 10.1113/jphysiol.2008.168005
- Issue published online: 13 MAR 2009
- Article first published online: 13 MAR 2009
- (Received 17 December 2008; accepted after revision 19 January 2009; first published online 26 January 2009)
Hormones such as glucagon are secreted by Ca2+-induced exocytosis of large dense-core vesicles, but the mechanisms involved have only been partially elucidated. Studies of pancreatic β-cells secreting insulin revealed that synaptotagmin-7 alone is not sufficient to mediate Ca2+-dependent insulin granule exocytosis, and studies of chromaffin cells secreting neuropeptides and catecholamines showed that synaptotagmin-1 and -7 collaborate as Ca2+ sensors for exocytosis, and that both are equally involved. As no other peptide secretion was analysed, it remains unclear whether synaptotagmins generally act as Ca2+ sensors in large dense-core vesicle exocytosis in endocrine cells, and if so, whether synaptotagmin-7 always functions with a partner in that role. In particular, far less is known about the mechanisms underlying Ca2+-triggered glucagon release from α-cells than insulin secretion from β-cells, even though insulin and glucagon together regulate blood glucose levels. To address these issues, we analysed the role of synaptotagmins in Ca2+-triggered glucagon exocytosis. Surprisingly, we find that deletion of a single synaptotagmin isoform, synaptotagmin-7, nearly abolished Ca2+-triggered glucagon secretion. Moreover, single-cell capacitance measurements confirmed that pancreatic α-cells lacking synaptotagmin-7 exhibited little Ca2+-induced exocytosis, whereas all other physiological and morphological parameters of the α-cells were normal. Our data thus identify synaptotagmin-7 as a principal Ca2+ sensor for glucagon secretion, and support the notion that synaptotagmins perform a universal but selective function as individually acting Ca2+ sensors in neurotransmitter, neuropeptide, and hormone secretion.