Glucose stimulates Ca2+ influx and insulin secretion in 2-week-old beta-cells lacking ATP-sensitive K+ channels.
In adult beta-cells glucose-induced insulin secretion involves two mechanisms (a) a K(ATP) channel-dependent Ca(2+) influx and rise of cytosolic [Ca(2+)](c) and (b) a K(ATP) channel-independent amplification of secretion without further increase of [Ca(2+)](c). Mice lacking the high affinity sulfonylurea receptor (Sur1KO), and thus K(ATP) channels, have been developed as a model of congenital hyperinsulinism. Here, we compared [Ca(2+)](c) and insulin secretion in overnight cultured islets from 2-week-old normal and Sur1KO mice. Control islets proved functionally mature: the magnitude and biphasic kinetics of [Ca(2+)](c) and insulin secretion changes induced by glucose, and operation of the amplifying pathway, were similar to adult islets. Sur1KO islets perifused with 1 mm glucose showed elevation of both basal [Ca(2+)](c) and insulin secretion. Stimulation with 15 mm glucose produced a transient drop of [Ca(2+)](c) followed by an overshoot and a sustained elevation, accompanied by a monophasic, 6-fold increase in insulin secretion. Glucose also increased insulin secretion when [Ca(2+)](c) was clamped by KCl. When Sur1KO islets were cultured in 5 instead of 10 mm glucose, [Ca(2+)](c) and insulin secretion were unexpectedly low in 1 mm glucose and increased following a biphasic time course upon stimulation by 15 mm glucose. This K(ATP) channel-independent first phase [Ca(2+)](c) rise was attributed to a Na(+)-, Cl(-)-, and Na(+)-pump-independent depolarization of beta-cells, leading to Ca(2+) influx through voltage-dependent calcium channels. Glucose indeed depolarized Sur1KO islets under these conditions. It is suggested that unidentified potassium channels are sensitive to glucose and subserve the acute and long-term metabolic control of [Ca(2+)](c) in beta-cells without functional K(ATP) channels.
Szollosi
Andras
A
Unit of Endocrinology and Metabolism, University of Louvain Faculty of Medicine, UCL 55.30, Avenue Hippocrate 55, B-1200 Brussels, Belgium.
Nenquin
Myriam
M
Aguilar-Bryan
Lydia
L
Bryan
Joseph
J
Henquin
Jean-Claude
JC
D018528:ATP-Binding Cassette Transporters / Q000235:genetics; D000255:Adenosine Triphosphate / Q000737:chemistry*; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D000242:Cyclic AMP / Q000378:metabolism; D005947:Glucose / Q000378:metabolism*; D006801:Humans; D007328:Insulin / Q000378:metabolism*; D000078790:Insulin Secretion; D050417:Insulin-Secreting Cells / Q000378:metabolism*; D007515:Islets of Langerhans / Q000378:metabolism; D007700:Kinetics; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D015221:Potassium Channels / Q000737:chemistry* / Q000235:genetics; D024661:Potassium Channels, Inwardly Rectifying / Q000235:genetics; D011955:Receptors, Drug / Q000235:genetics; D064233:Sulfonylurea Receptors
D018528:ATP-Binding Cassette Transporters; D007328:Insulin; D015221:Potassium Channels; D024661:Potassium Channels, Inwardly Rectifying; D011955:Receptors, Drug; D064233:Sulfonylurea Receptors; D000255:Adenosine Triphosphate; D000242:Cyclic AMP; D005947:Glucose; D002118:Calcium