SNAREing voltage-gated K+ and ATP-sensitive K+ channels: tuning beta-cell excitability with syntaxin-1A and other exocytotic proteins

Endocr Rev. 2007 Oct;28(6):653-63. doi: 10.1210/er.2007-0010. Epub 2007 Sep 18.

Abstract

The three SNARE (soluble N-ethylmaleimide-sensitive factor attachment protein receptor) 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 Ca(2+) channels to form an excitosome that precisely regulates calcium entry at the site of exocytosis. In pancreatic islet beta-cells, ATP-sensitive K(+) (K(ATP)) channel closure by high ATP concentration leads to membrane depolarization, voltage-dependent Ca(2+) channel 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 physically interacts with Kv2.1 (the predominant Kv in beta-cells) and the sulfonylurea receptor subunit of beta-cell K(ATP) channel to modify their gating behaviors. A model has proposed that the conformational changes of syntaxin-1A during exocytosis induce distinct functional modulations of K(ATP) 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, and guanyl nucleotide exchange factor II, have also been implicated in direct or indirect regulation of beta-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 beta-cell excitability via modulation of ion channel gating.

Publication types

  • Research Support, Non-U.S. Gov't
  • Review

MeSH terms

  • Animals
  • Exocytosis / physiology
  • Humans
  • Insulin-Secreting Cells / metabolism*
  • Ion Channel Gating / physiology*
  • KATP Channels / metabolism*
  • Potassium Channels, Voltage-Gated / metabolism*
  • SNARE Proteins / physiology*
  • Syntaxin 1 / physiology*

Substances

  • KATP Channels
  • Potassium Channels, Voltage-Gated
  • SNARE Proteins
  • Syntaxin 1