Quoix N, Cheng-Xue R, Mattart L, Zeinoun Z, Guiot Y, Beauvois MC, Henquin JC, Gilon P. Glucose and pharmacological modulators of ATP-sensitive K+ channels control [Ca2+]c by different mechanisms in isolated mouse alpha-cells.
Diabetes 2009;
58:412-21. [PMID:
19008345 PMCID:
PMC2628615 DOI:
10.2337/db07-1298]
[Citation(s) in RCA: 62] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
OBJECTIVE
We studied how glucose and ATP-sensitive K(+) (K(ATP)) channel modulators affect alpha-cell [Ca(2+)](c).
RESEARCH DESIGN AND METHODS
GYY mice (expressing enhanced yellow fluorescent protein in alpha-cells) and NMRI mice were used. [Ca(2+)](c), the K(ATP) current (I(KATP), perforated mode) and cell metabolism [NAD(P)H fluorescence] were monitored in single alpha-cells and, for comparison, in single beta-cells.
RESULTS
In 0.5 mmol/l glucose, [Ca(2+)](c) oscillated in some alpha-cells and was basal in the others. Increasing glucose to 15 mmol/l decreased [Ca(2+)](c) by approximately 30% in oscillating cells and was ineffective in the others. alpha-Cell I(KATP) was inhibited by tolbutamide and activated by diazoxide or the mitochondrial poison azide, as in beta-cells. Tolbutamide increased alpha-cell [Ca(2+)](c), whereas diazoxide and azide abolished [Ca(2+)](c) oscillations. Increasing glucose from 0.5 to 15 mmol/l did not change I(KATP) and NAD(P)H fluorescence in alpha-cells in contrast to beta-cells. The use of nimodipine showed that L-type Ca(2+) channels are the main conduits for Ca(2+) influx in alpha-cells. gamma-Aminobutyric acid and zinc did not decrease alpha-cell [Ca(2+)](c), and insulin, although lowering [Ca(2+)](c) very modestly, did not affect glucagon secretion.
CONCLUSIONS
alpha-Cells display similarities with beta-cells: K(ATP) channels control Ca(2+) influx mainly through L-type Ca(2+) channels. However, alpha-cells have distinct features from beta-cells: Most K(ATP) channels are already closed at low glucose, glucose does not affect cell metabolism and I(KATP), and it slightly decreases [Ca(2+)](c). Hence, glucose and K(ATP) channel modulators exert distinct effects on alpha-cell [Ca(2+)](c). The direct small glucose-induced drop in alpha-cell [Ca(2+)](c) contributes likely only partly to the strong glucose-induced inhibition of glucagon secretion in islets.
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