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J Biol Chem. 2018 May 4;293(18):6893-6904. doi: 10.1074/jbc.RA118.002703. Epub 2018 Mar 16.

Kv2.1 clusters on β-cell plasma membrane act as reservoirs that replenish pools of newcomer insulin granule through their interaction with syntaxin-3.

Author information

1
From the Departments of Medicine and Physiology, University of Toronto, Toronto, Ontario M5S 1A8, Canada and.
2
the Department of Epidemiology and Health Statistics, School of Public Health and Family Medicine, Capital Medical University, Beijing 100050, China.

Abstract

The voltage-dependent K+ (Kv) channel Kv2.1 is a major delayed rectifier in many secretory cells, including pancreatic β cells. In addition, Kv2.1 has a direct role in exocytosis at an undefined step, involving SNARE proteins, that is independent of its ion-conducting pore function. Here, we elucidated the precise step in exocytosis. We previously reported that syntaxin-3 (Syn-3) is the key syntaxin that mediates exocytosis of newcomer secretory granules that spend minimal residence time on the plasma membrane before fusion. Using high-resolution total internal reflection fluorescence microscopy, we now show that Kv2.1 forms reservoir clusters on the β-cell plasma membrane and binds Syn-3 via its C-terminal C1b domain, which recruits newcomer insulin secretory granules into this large reservoir. Upon glucose stimulation, secretory granules were released from this reservoir to replenish the pool of newcomer secretory granules for subsequent fusion, occurring just adjacent to the plasma membrane Kv2.1 clusters. C1b deletion blocked the aforementioned Kv2.1-Syn-3-mediated events and reduced fusion of newcomer secretory granules. These insights have therapeutic implications, as Kv2.1 overexpression in type-2 diabetes rat islets restored biphasic insulin secretion.

KEYWORDS:

Kv2.1; insulin secretion; newcomer insulin granule; pancreatic islet; plasma membrane; potassium channel; syntaxin-3; vesicles

PMID:
29549124
PMCID:
PMC5936832
DOI:
10.1074/jbc.RA118.002703
[Indexed for MEDLINE]
Free PMC Article

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