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-Cell Excitability with Syntaxin-1A and Other Exocytotic Proteins
Department of Physiology, China Medical University, Taichung 40402, Taiwan; Graduate Institute of Neural and Cognitive Sciences, China Medical University, Taichung 40402, Taiwan; Departments of Medicine and Physiology, University of Toronto, Toronto, Canada
* To whom correspondence should be addressed. E-mail: ymleung{at}mail.cmu.edu.tw or herbert.gaisano{at}utoronto.ca.
The three SNARE (soluble N-ethylmaleimide-sensitive factor attachment protein receptors) proteins, syntaxin, SNAP25 (synaptosome-associated protein of 25 kDa) and synaptobrevin, constitute the minimal machinery for exocytosis in secretory cells such as neurons and neuroendocrine cells by forming a series of complexes prior to and during vesicle fusion. It was subsequently found that these SNARE proteins not only participate in vesicle fusion, but also tether with voltage-dependent Ca2+ channels (VDCC) to form an excitosome that precisely regulates calcium entry at the site of exocytosis. In pancreatic islet
-cells, ATP-sensitive K+ (KATP) channel closure by high ATP concentration leads to membrane depolarization, VDCC opening and insulin secretion, whereas subsequent opening of voltage-gated K+ (Kv) channels repolarizes the cell to terminate exocytosis. We have obtained evidence that syntaxin-1A (Syn-1A) physically interacts with Kv2.1 (the predominant Kv in
-cells) and the sulfonylurea receptor subunit of
-cell KATP channel to modify their gating behaviors. A model has proposed that the conformational changes of Syn-1A during exocytosis induce distinct functional modulations of KATP and Kv2.1 channels in a manner that optimally regulates cell excitability and insulin secretion. Other proteins involved in exocytosis, such as Munc-13, tomosyn, rab3a-interacting molecule (RIM), and guanyl nucleotide exchange factor II (GEFII), have also been implicated in direct or indirect regulation of
-cell ion channel activities and excitability. This review discusses this interesting aspect that exocytotic proteins not only promote secretion per se, but also fine-tune
-cell excitability via modulation of ion channel gating.
-cells
Kv channels
KATP channels
exocytosis
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