title: Ouabain suppresses glucose-induced mitochondrial ATP production and insulin release by generating reactive oxygen species in pancreatic islets.
abstract: We examined the effects of reduced Na(+)/K(+)-ATPase activity on mitochondrial ATP production and insulin release from rat islets. Ouabain, an inhibitor of Na(+)/K(+)-ATPase, augmented 16.7 mmol/l glucose-induced insulin release in the early period but suppressed it after a delay of 20-30 min. Unexpectedly, the ATP content in an islet decreases in the presence of 16.7 mmol/l glucose when Na(+)/K(+)-ATPase activity is diminished by ouabain, despite the reduced consumption of ATP by the enzyme. Ouabain also suppressed the increment of ATP content produced by glucose even in Ca(2+)-depleted or Na(+)-depleted conditions. That mitochondrial membrane hyperpolarization and O(2) consumption in islets exposed to 16.7 mmol/l glucose were suppressed by ouabain indicates that the glycoside inhibits mitochondrial respiration but does not produce uncoupling. Ouabain induced mitochondrial reactive oxygen species (ROS) production that was blocked by myxothiazol, an inhibitor of site III of the mitochondrial respiratory chain. An antioxidant, alpha-tocopherol, also blocked ouabain-induced ROS production as well as the suppressive effect of ouabain on ATP production and insulin release. However, ouabain did not directly affect the mitochondrial ATP production originating from succinate and ADP. These results indicate that ouabain suppresses mitochondrial ATP production by generating ROS via transduction, independently of the intracellular cationic alternation that may account in part for the suppressive effect on insulin secretion.
authors.affiliation: Department of Metabolism and Clinical Nutrition, Graduate School of Medicine, Kyoto University, Kyoto, Japan. kajikawa@metab.kuhp.kyoto-u.ac.jp
authors.forename: Mariko
authors.initials: M
authors.lastname: Kajikawa
authors.forename: Shimpei
authors.initials: S
authors.lastname: Fujimoto
authors.forename: Yoshiyuki
authors.initials: Y
authors.lastname: Tsuura
authors.forename: Eri
authors.initials: E
authors.lastname: Mukai
authors.forename: Tomomi
authors.initials: T
authors.lastname: Takeda
authors.forename: Yoshiyuki
authors.initials: Y
authors.lastname: Hamamoto
authors.forename: Mihoko
authors.initials: M
authors.lastname: Takehiro
authors.forename: Jun
authors.initials: J
authors.lastname: Fujita
authors.forename: Yuichiro
authors.initials: Y
authors.lastname: Yamada
authors.forename: Yutaka
authors.initials: Y
authors.lastname: Seino
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism*; D000818:Animals; D002259:Carbonyl Cyanide p-Trifluoromethoxyphenylhydrazone / Q000494:pharmacology; D005947:Glucose / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D006861:Hydrogen Peroxide / Q000494:pharmacology; D066298:In Vitro Techniques; D007328:Insulin / Q000378:metabolism*; D000078790:Insulin Secretion; D007515:Islets of Langerhans / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D007700:Kinetics; D008928:Mitochondria / Q000187:drug effects / Q000378:metabolism*; D010042:Ouabain / Q000494:pharmacology*; D010101:Oxygen Consumption / Q000502:physiology*; D051381:Rats; D017382:Reactive Oxygen Species / Q000378:metabolism*; D014810:Vitamin E / Q000494:pharmacology
chemical_list: D007328:Insulin; D017382:Reactive Oxygen Species; D014810:Vitamin E; D002259:Carbonyl Cyanide p-Trifluoromethoxyphenylhydrazone; D010042:Ouabain; D000255:Adenosine Triphosphate; D006861:Hydrogen Peroxide; D005947:Glucose