Glucose stimulates voltage- and calcium-dependent inositol trisphosphate production and intracellular calcium mobilization in insulin-secreting beta TC3 cells.
The cellular processes leading to a rise in the intracellular free Ca2+ concentration ([Ca2+]i) after glucose stimulation and K+ depolarization were investigated in insulin-secreting beta TC-3 cells. Stimulation with 11.2mM glucose causes inositol 1,4,5-trisphosphate production and release of Ca2+ from intracellular stores. A strong correlation was observed between the changes in Ins(1,4,5)P3 concentration and the rise in [Ca2+]i, consistent with the former compound being responsible for release of Ca2+ from intracellular stores. The increase in Ins(1,4,5)P3 production was reduced by 68 +/- 4% when [Ca2+]i was kept low on glucose stimulation by loading cells with the Ca2+ chelator 1,2-bis(2-aminophenoxy)ethane-NNN'N'-tetra-acetic acid (BAPTA). The Ins(1,4,5)P3 production was prevented in cells hyperpolarized with diazoxide, an opener of ATP-sensitive K+-channels, consistent with the membrane potential controlling the rate of Ins(1,4,5)P3 synthesis. Depolarizing K+ concentrations evoked changes in [Ca2+]i and Ins(1,4,5)P3 production in both the presence and the absence of extracellular Ca2+, and from the relation between the extracellular K+ concentration and membrane potential we found a half-maximal Ins(1,4,5)P3 production by a 28mV depolarization from a resting potential of -56mV and by a rise in [Ca2+]i of 390nM. We conclude that stimulation-induced changes in membrane potential and [Ca2+]i are important in controlling Ins(1,4,5)P3 production in beta TC-3 cells and that glucose-stimulated Ca2+ mobilization from intracellular stores is due to voltage-dependent Ins(1,45)P3 production and depends on the concurrent increase in [Ca2+]i.
Gromada
J
J
Department of Medical Physiology, The Panum Institute, University of Copenhagen, Denmark.
Frøkjaer-Jensen
J
J
Dissing
S
S
D000818:Animals; D002118:Calcium / Q000378:metabolism* / Q000494:pharmacology; D015220:Calcium Channels / Q000187:drug effects / Q000378:metabolism; D003981:Diazoxide / Q000494:pharmacology; D005947:Glucose / Q000494:pharmacology*; D015544:Inositol 1,4,5-Trisphosphate / Q000096:biosynthesis* / Q000378:metabolism; D007295:Inositol Phosphates / Q000032:analysis; D007328:Insulin / Q000378:metabolism*; D000078790:Insulin Secretion; D007340:Insulinoma; D007515:Islets of Langerhans / Q000187:drug effects / Q000378:metabolism*; D007700:Kinetics; D008564:Membrane Potentials; D051379:Mice; D008822:Mice, Transgenic; D011188:Potassium / Q000494:pharmacology; D014407:Tumor Cells, Cultured; D010738:Type C Phospholipases / Q000378:metabolism
D015220:Calcium Channels; D007295:Inositol Phosphates; D007328:Insulin; D015544:Inositol 1,4,5-Trisphosphate; D010738:Type C Phospholipases; D005947:Glucose; D003981:Diazoxide; D011188:Potassium; D002118:Calcium