Regulation of intracellular ATP concentration under conditions of reduced ATP consumption in pancreatic islets.
ATP is the most important factor in glucose-induced insulin secretion in pancreatic beta-cells, but examination of intracellular differences in ATP concentration is difficult because ATP production and consumption occur simultaneously. In the present study, we measured the ATP concentration under the condition of a reduced ATP requirement by omitting extracellular Ca(2+) and inhibiting Na-K ATPase. The ATP concentration in islets incubated with 16.7 mM glucose in the absence of Ca(2+) for 30 min was increased by about 1. 9-fold more than in the presence of Ca(2+). The increment was extracellular Ca(2+)-dependent, and was completely abolished by the metabolic inhibitors dinitrophenol and iodoacetic acid. The Ca channel blockers including nitrendipine and Ni(2+) did not affect the ATP concentration in islets incubated with 16.7 mM glucose in the presence of Ca(2+). However, when thapsigargin and suramin, inhibitors of Ca-ATPase at the endoplasmic reticulum, were added to Ca channel blockers in the presence of ambient Ca(2+), the intraislet ATP content was increased, similarly to that under Ca-free conditions. But thapsigargin did not further augment the ATP concentration in the islet with 16.7 mM glucose in the absence of Ca(2+). On the other hand, the suppression of Na-K ATPase by ouabain rather reduced the ATP concentration augmented by omission of extracellular Ca(2+). In addition, vanadate, a blocker of Ca-ATPase at the plasma membrane, failed to increase the ATP concentration in the islets. These data suggest that the increment of ATP concentration in the absence of Ca(2+) is attributable to the reduced ATP requirement due to stopping of the Ca-ATPase activity at the endoplasmic reticulum, and that the intracellular ATP concentration is differently regulated by Na-K ATPase at plasma membrane and by Ca-ATPase at endoplasmic reticulum.
Tsuura
Y
Y
Graduate School of Medicine, Kyoto University, Kyoto, 606-8507, Japan.
Fujimoto
S
S
Kajikawa
M
M
Ishida
H
H
Seino
Y
Y
D000255:Adenosine Triphosphate / Q000378:metabolism*; D000818:Animals; D000963:Antimetabolites / Q000494:pharmacology; D002118:Calcium / Q000494:pharmacology; D002121:Calcium Channel Blockers / Q000494:pharmacology; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors; D004791:Enzyme Inhibitors / Q000494:pharmacology; D066298:In Vitro Techniques; D007424:Intracellular Fluid / Q000378:metabolism; D007515:Islets of Langerhans / Q000187:drug effects / Q000378:metabolism*; D008297:Male; D010042:Ouabain / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D000254:Sodium-Potassium-Exchanging ATPase / Q000037:antagonists & inhibitors
D000963:Antimetabolites; D002121:Calcium Channel Blockers; D004791:Enzyme Inhibitors; D010042:Ouabain; D000255:Adenosine Triphosphate; D000252:Calcium-Transporting ATPases; D000254:Sodium-Potassium-Exchanging ATPase; D002118:Calcium