Insulin secretagogues, but not glucose, stimulate an increase in [Ca2+]i in the fetal human and porcine beta-cell.
Fetal pancreatic beta-cells release insulin poorly in response to glucose; however, the cellular mechanism for this is unknown. By using fura-2 to measure changes in the cytoplasmic free Ca(2+) concentration in beta-cells, we examined human/porcine fetal islet-like cell clusters (ICCs) and human adult islets for the presence of functional K(+)(ATP) and voltage-activated Ca(2+) ion channels. The effects of glucose, glyceraldehyde, leucine, KCl, and the channel effectors glipizide and BAY K8644 were studied. In fetal human/porcine ICCs and adult islets, KCl, glipizide, and BAY K8644 increased [Ca(2+)](i). Both glucose and glyceraldehyde increased [Ca(2+)](i) in islets but had no effect on ICCs. Leucine increased [Ca(2+)](i) in islets and porcine but not human ICCs. We hypothesize that the beneficial effect of leucine in fetal porcine, but not human ICCs, is attributable to time-dependent maturation of the beta-cells, because porcine ICCs examined were at 87% of the gestational period, and human ICCs were at 42%. Our data demonstrate that both K(+)(ATP) and voltage-activated Ca(2+) channels, required for glucose-stimulated increase in [Ca(2+)](i), are functional early in gestation. This suggests that the cause of the immaturity of fetal human/porcine beta-cells is at a more proximal step of glucose-induced metabolism than the channels on the cell surface.
Weinhaus
Anthony J
AJ
Department of Medicine, University of Sydney, NSW 2006, Australia.
Tabiin
Muhammad T
MT
Poronnik
Philip
P
Palma
Catalina A
CA
Cook
David I
DI
Tuch
Bernard E
BE
D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002120:Calcium Channel Agonists / Q000494:pharmacology; D000242:Cyclic AMP / Q000494:pharmacology; D005333:Fetus / Q000187:drug effects / Q000378:metabolism; D005913:Glipizide / Q000494:pharmacology; D005947:Glucose / Q000494:pharmacology*; D006801:Humans; D066298:In Vitro Techniques; D007328:Insulin / Q000378:metabolism*; D000078790:Insulin Secretion; D007425:Intracellular Membranes / Q000378:metabolism; D007515:Islets of Langerhans / Q000196:embryology* / Q000378:metabolism; D011189:Potassium Chloride / Q000494:pharmacology; D013552:Swine
D002120:Calcium Channel Agonists; D007328:Insulin; D011189:Potassium Chloride; D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester; D000242:Cyclic AMP; D005947:Glucose; D002118:Calcium; D005913:Glipizide