Free radicals uncouple the sodium pump in pig coronary artery.
Free radicals may impair vital functions of several types of tissues including coronary artery smooth muscle. Because the Na+ pump plays a key role in maintaining coronary tone, the effects of superoxide and peroxide on this protein were examined. Ouabain-sensitive Rb+ uptake by denuded coronary artery rings was used in lieu of K+ transport by this pump. It was inhibited by exposing the rings for 90 min either to peroxide [50% inhibitory concentration (IC50) = 0.56 +/- 0.18 mM] or to superoxide generated by xanthine oxidase (XO; 0.3 mM xanthine and xanthine oxidase, IC50 = 0.08 +/- 02 mU/ml). The effect of peroxide was not overcome by superoxide dismutase and that of superoxide was not prevented by catalase. K(+)-activated ouabain-sensitive hydrolysis of p-nitrophenyl phosphate in the plasma membrane-enriched fraction isolated from the coronary artery smooth muscle was monitored as the hydrolytic activity of the Na+ pump. It was inhibited by exposing the membranes only to very high concentrations of peroxide (IC50 = 9.85 +/- 3.5 mM) or XO (IC50 = 5 +/- 2 mU/ml). The exposure to 2.5 mM H2O2 or 0.5 mU/ml XO reduced the Na(+)-dependent acylphosphate levels only by 41 +/- 3 and 30 +/- 4%, respectively even though either inhibited the Rb+ uptake by > 80%. Thus superoxide and peroxide uncoupled the hydrolytic activity of the Na+ pump from Rb+ uptake. We speculate that such an uncoupling in ischemia and reperfusion would result in dual damage: ion imbalance and continuous hydrolysis of ATP in the cells that are already starved.
Elmoselhi
A B
AB
Department of Biomedical Sciences, McMaster University, Hamilton, Ontario, Canada.
Butcher
A
A
Samson
S E
SE
Grover
A K
AK
D009597:4-Nitrophenylphosphatase / Q000378:metabolism; D000818:Animals; D001158:Arteries / Q000196:embryology; D001692:Biological Transport / Q000187:drug effects; D003331:Coronary Vessels / Q000378:metabolism*; D006868:Hydrolysis / Q000187:drug effects; D066298:In Vitro Techniques; D010545:Peroxides / Q000494:pharmacology; D017382:Reactive Oxygen Species / Q000494:pharmacology*; D012413:Rubidium / Q000493:pharmacokinetics; D000254:Sodium-Potassium-Exchanging ATPase / Q000187:drug effects*; D013481:Superoxides / Q000494:pharmacology; D013552:Swine
D010545:Peroxides; D017382:Reactive Oxygen Species; D013481:Superoxides; D009597:4-Nitrophenylphosphatase; D000254:Sodium-Potassium-Exchanging ATPase; D012413:Rubidium