Modulation of sarcoplasmic reticulum gene expression due to ischemia-reperfusion in isolated rat heart

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Temsah, Rana M.
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Ischemia-reperfusion (IR) i a common feature present in different pathologies such as acute myocardial infarction and ischemic heart disease as well as in various clinical maneuvers following cardiac bypass surgery, heart transplantation, coronary angioplasty and thrombolysis. This study addressed the following hypothesis: IR induces long-term cardiac dysfunction in remnant myocytes by modulating SR mRNA expression for the Ca2+-cycling proteins such as Ca2+-pump ATPase, Ca2+-release channels, phospholamban and calsequestrin. Thirty minutes of global ischemia followed by 60 min of reperfusion of the isolated rat heart resulted in impaired cardiac performance, SR function as well as reduced levels of SR Ca2+-cycling proteins. These changes were accompanied by depressed mRNA expression of SR proteins. In view of the occurrence of hypoxia and substrate lack in the ischemic heart, we investigated the role of these factors in the alterations observed during reperfusion. Hearts perfused with oxygenated medium containing glucose after 30 min of oxygen or glucose deprivation showed partial recovery of heart function with normal levels of expression of the SR mRNA and proteins. Hearts perfused with normal medium after deprivation of both glucose and oxygen showed partial functional recovery with normal levels of SR protein expression despite depressed transcript levels of the SR Ca2+-cycling proteins. This implicates that both hypoxia and gluco se deprivation during the ischemic phase are important factors for the occurrence of IR-induced injury. The role of oxidative stress in IR induced injury was investigated by treating IR hearts with superoxide dismutase plus catalase. This treatment improved cardiac performance, SR function and mRNA expression in the IR hearts. Alterations provoked due to oxidative stress were confirmed when hearts treated with H2O2 and xanthine plus xanthine oxidase (source of superoxide radical) showed results similar to those observed in the IR hearts. Some experiments were also carried out to examine the effect of Ca 2+-overload, which occurs during the reperfusion phase of IR, on cardiac performance and SR function. For this purpose, Ca2+-overload was induced by perfusing hearts for 5 min with a Ca2+-free buffer followed by 30 min of perfusion with a Ca2+-containing medium. Ca2+-depleted/repleted hearts showed impaired functional recovery with drastic decrease in the SR function, protein content and mRNA expression. These results indicate that both oxidative stress and Ca 2+-overload are major players in inducing changes in SR function and mRNA expression in the IR hearts. IR hearts treated with B-adrenoceptor blockers (atenolol or propranolol) have shown marked protection of cardiac performance, SR function and protein and mRNA expression of the SR proteins. (Abstract shortened by UMI.)