Glucose-induced increase in cytoplasmic pH in pancreatic beta-cells is mediated by Na+/H+ exchange, an effect not dependent on protein kinase C.
Glucose-induced changes in cytoplasmic pH (pHi) were investigated using pancreatic beta-cells isolated from obese hyperglycemic mice. Glucose, at concentrations above 3-5 mM, depolarized the beta-cell and increased pHi, cytoplasmic free Ca2+ ([Ca2+]i), and insulin release. This increase in pHi was dependent on the presence of extracellular Na+ and was inhibited by 5-(N-ethyl-N-isopropyl) amiloride, a blocker of Na+/H+ exchange. Stimulation of protein kinase C with phorbol ester also induced an alkalinization. However, when protein kinase C activity was down-regulated, glucose stimulation still induced alkalinization. At 20 mM glucose, 10 mM NH4Cl induced a marked rise in pHi, paralleled by repolarization, inhibition of electrical activity, and decreases in both [Ca2+]i and insulin release. Reduction in [Ca2+]i was prevented by 200 microM tolbutamide, but not by 10 mM tetraethylammonium. At 4 mM glucose, NH4Cl induced a transient increase in insulin release, without changing [Ca2+]i. Exposure of beta-cells to 10 mM sodium acetate caused a persistent decrease in pHi, an effect paralleled by a small transient increase in [Ca2+]i. Acidification per se did not change the beta-cell sensitivity to glucose, not excluding that the activity of the ATP-regulated K+ channels may be modulated by changes in pHi.
Juntti-Berggren
L
L
Department of Medical Cell Biology, Biomedicum, University of Uppsala, Sweden.
Arkhammar
P
P
Nilsson
T
T
Rorsman
P
P
Berggren
P O
PO
D000584:Amiloride / Q000031:analogs & derivatives / Q000494:pharmacology; D000643:Ammonium Chloride / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism; D002352:Carrier Proteins / Q000378:metabolism*; D002478:Cells, Cultured; D005947:Glucose / Q000494:pharmacology*; D006863:Hydrogen-Ion Concentration; D007328:Insulin / Q000378:metabolism; D000078790:Insulin Secretion; D007515:Islets of Langerhans / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D007700:Kinetics; D008564:Membrane Potentials / Q000187:drug effects; D051379:Mice; D008820:Mice, Obese; D011188:Potassium / Q000494:pharmacology; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000378:metabolism*; D012964:Sodium / Q000378:metabolism*; D017923:Sodium-Hydrogen Exchangers; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D014044:Tolbutamide / Q000494:pharmacology
D002352:Carrier Proteins; D007328:Insulin; D017923:Sodium-Hydrogen Exchangers; D000643:Ammonium Chloride; D000584:Amiloride; D014044:Tolbutamide; D012964:Sodium; D011493:Protein Kinase C; D005947:Glucose; D013755:Tetradecanoylphorbol Acetate; D011188:Potassium; D002118:Calcium; C039614:ethylisopropylamiloride