Abstract
It has been postulated that disturbances of ionic homeostasis may determine the vulnerability of the heart to reperfusion-induced injury, and that reactive oxygen species produced during reperfusion, cause oxidant stress to membrane protein or lipid that leads to disturbances of ionic homeostasis and arrhythmias. To test this hypothesis, we studied the efficacies of various reactive oxygen species scavengers in reducing ischemia-reperfusion (I/R) -induced myocardial injury in isolated perfused rat hearts. The effect of in vitro free radical generating system consisting of hypoxanthine (hyX) and xanthine oxidase (XO) on sarcoplasmic reticulum (SR) function was also investigated. In I/R hearts, the contractile function and coronary flow were reduced; reperfusion with histidine or a cocktail of superoxide dismutase (SOD) -catalase-mannitol resulted in significant protection against the effect of I/R. The incidence of arrhythmias during reperfusion was 100% in I/R hearts; the duration of arrhythmias was shortened with histidine or with SOD-catalase-mannitol. The decreased duration of normal sinus rhythm in I/R hearts was also protected with histidine or SOD-catalase-mannitol. The SR function assessed by oxalate-supported Ca2+ uptake rate in cell free preparations in the presence or absence of ruthenium red, a selective SR Ca2+-release channel blocker, was depressed by exposure to hyX-XO reaction. The observed effect of hyX-XO was SOD-inhibitable and was protected by SOD-catalase-mannitol. In samples where the Ca2+-release channel was blocked with ruthenium red, no changes in Ca2+ uptake rates were noted after ischemia only; the Ca2+ uptake rates in the presence of ruthenium red decreased in samples from ischemia-reperfused hearts, suggesting Ca2+-release channel dysfunction caused by oxygen-derived free radicals generated during reperfusion. Exposure of isolated heavy SR to hyX-XO reaction produced potent increase in Ca2+ efflux; the effect of hyX-XO reaction was protected by SOD or by established optimal conditions for specific closure of heavy SR Ca2+-release channel by ryanodine. Based on these lines of results, we conclude that the action of reactive oxygen species (possibly, superoxide radicals or singlet molecular oxygen) may be mediated in part through SR Ca2+-release channel, thereby causing Ca2+ overload linked to arrhythmogenic electrophysiological changes.
