Glucose or Insulin, but not Zinc Ions, Inhibit Glucagon Secretion From Mouse Pancreatic α-Cells

Glucose or Insulin, but not Zinc Ions, Inhibit Glucagon Secretion From Mouse Pancreatic α-Cells Magalie A. Ravier and Guy A. Rutter From the Henry Wellcome Laboratories for Integrated Cell Signalling and Department of Biochemistry, School of Medical Sciences, University Walk, University of Bristol, Bristol, U.K. Address correspondence and reprint requests to Professor Guy A. Rutter, Department of Biochemistry, School of Medical Sciences, University of Bristol, University Walk, Bristol, BS8 1TD, U.K. E-mail: g.a.rutter{at}bristol.ac.uk Abstract The mechanisms by which hypoglycemia stimulates glucagon release are still poorly understood. In particular, the relative importance of direct metabolic coupling versus paracrine regulation by β-cell secretory products is unresolved. Here, we compare the responses to glucose of 1 ) α-cells within the intact mouse islet, 2 ) dissociated α-cells, and 3 ) clonal αTC1-9 cells. Free cytosolic concentrations of ATP ([ATP] c ) or Ca 2+ ([Ca 2+ ] c ) were imaged using α-cell–targeted firefly luciferase or a green fluorescent protein–based Ca 2+ probe (“pericam”), respectively. Consistent with a direct effect of glucose on α-cell oxidative metabolism, an increase in glucose concentration (from 0 or 3 mmol/l to 20 mmol/l) increased [ATP] c by 7–9% in α-cells within the intact islet and by ∼4% in αTC1-9 cells. Moreover, glucose also dose-dependently decreased the frequency of [Ca 2+ ] c oscillations in both dissociated α-cells and αTC1-9 cells. Although the effects of glucose were mimicked by exogenous insulin, they were preserved when insulin signaling was blocked with wortmannin. Addition of ZnCl 2 slightly increased the frequency of [Ca 2+ ] c oscillations but failed to affect glucagon release from either islets or αTC1-9 cells under most conditions. We conclude that glucose and insulin, but not Zn 2+ ions, independently suppress glucagon secretion in the mouse. [ATP]c, cytosolic concentration of ATP [Ca2+]c, cytosolic concentration of Ca2+ KATP channel, ATP-sensitive K+ channel KRBB, Krebs-Ringer bicarbonate buffer PPG, preproglucagon Footnotes The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact. Accepted March 10, 2005. Received November 9, 2004. DIABETES