Glucose or insulin, but not zinc ions, inhibit glucagon secretion from mouse pancreatic alpha-cells.
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 beta-cell secretory products is unresolved. Here, we compare the responses to glucose of 1) alpha-cells within the intact mouse islet, 2) dissociated alpha-cells, and 3) clonal alphaTC1-9 cells. Free cytosolic concentrations of ATP ([ATP](c)) or Ca(2+) ([Ca(2+)](c)) were imaged using alpha-cell-targeted firefly luciferase or a green fluorescent protein-based Ca(2+) probe ("pericam"), respectively. Consistent with a direct effect of glucose on alpha-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 alpha-cells within the intact islet and by approximately 4% in alphaTC1-9 cells. Moreover, glucose also dose-dependently decreased the frequency of [Ca(2+)](c) oscillations in both dissociated alpha-cells and alphaTC1-9 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 alphaTC1-9 cells under most conditions. We conclude that glucose and insulin, but not Zn(2+) ions, independently suppress glucagon secretion in the mouse.
Ravier
Magalie A
MA
Department of Biochemistry, School of Medical Sciences, University of Bristol, University Walk, Bristol, BS8 1TD, UK.
Rutter
Guy A
GA
D000255:Adenosine Triphosphate / Q000502:physiology; D000818:Animals; D002118:Calcium / Q000502:physiology; D002460:Cell Line; D002478:Cells, Cultured; D002999:Clone Cells; D005934:Glucagon / Q000378:metabolism*; D005947:Glucose / Q000494:pharmacology*; D007328:Insulin / Q000494:pharmacology*; D007515:Islets of Langerhans / Q000187:drug effects* / Q000378:metabolism*; D051379:Mice; D015032:Zinc / Q000494:pharmacology*
D007328:Insulin; D000255:Adenosine Triphosphate; D005934:Glucagon; D005947:Glucose; D015032:Zinc; D002118:Calcium