Coronary artery contractility, Na(+)-pump and oxygen radicals

Oxygen radicals accumulated during ischemia and reperfusion may affect coronary contractility by endothelium dependent and independent pathways one of which may involve Na(+)-pump. Here we report a contractility assay for Na(+)-pump in pig coronary artery and use it to examine the effects of hydrogen peroxide and superoxide. Coronary artery rings contracted in a K(+)-free Krebs solution and relaxed upon subsequent exposure to K+. The relaxation approximated a single exponential decay whose rate constant depended on [K+]2. This K(+)-induced relaxation was abolished by ouabain and was attributed to Na(+)-pump. In tissues pretreated with peroxide, the rate of relaxation of the K(+)-free contracted arteries decreased with an IC50 = 1.6 +/- 0.6 mmol/l for peroxide. Another set of tissues was pretreated with the superoxide generating system containing 0.3 mmol/l xanthine + varying concentrations of xanthine oxidase (XO) and precontracted in K(+)-free Krebs solution. The rate of the K(+)-induced relaxation decreased with IC50 = 24 +/- 8 mU/ml for XO. Thus, using the relaxation assay we conclude that exposing coronary arteries to oxygen radicals can damage Na(+)-pumps.