Glucose inhibits insulin release when not promoting the entry of calcium into the beta-cells.
The basal Ca2+ permeability of islets from ob/ob-mice was raised by culture in a Ca2+-deficient medium. The resulting secretory activity upon transfer to a higher Ca2+ concentration was significantly inhibited by 6 mM glucose although higher concentrations of the sugar further stimulated insulin release. In the presence theophylline, the inhibitory effect of 6 mM glucose was altered into a stimulatory one. After blocking the voltage-dependent channels for Ca2+ with D-600, 20 mM glucose did not enhance but significantly inhibited insulin release. The demonstration of a paradoxical glucose inhibition of insulin release is in accordance with recent reports that the sugar not only increases but also can lower the cytoplasmic Ca2+ activity in the pancreatic beta-cells.
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D005711:Gallopamil / Q000494:pharmacology; D005947:Glucose / Q000494:pharmacology*; D007328:Insulin / Q000378:metabolism*; D007515:Islets of Langerhans / Q000378:metabolism*; D051379:Mice; D008820:Mice, Obese; D013806:Theophylline / Q000494:pharmacology
D007328:Insulin; D005711:Gallopamil; D013806:Theophylline; D005947:Glucose; D002118:Calcium