Fostriecin, an Inhibitor of Protein Phosphatase 2A, Limits Myocardial Infarct Size Even When Administered After Onset of Ischemia

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Abstract
Background —The role of protein phosphatases (PPs) during ischemic preconditioning in the rabbit heart was examined. Methods and Results —Fostriecin, a potent inhibitor of PP2A, was administered to isolated rabbit hearts starting either 15 minutes before or 10 minutes after the onset of a 30-minute period of regional ischemia and continuing until the onset of reperfusion. After 2 hours of reperfusion, infarct size was measured with triphenyltetrazolium chloride. In a second study with isolated rabbit cardiomyocytes, the effect of fostriecin pretreatment was assessed by measuring changes in cell osmotic fragility during simulated ischemia. PP1 and PP2A activities of isolated control and ischemically preconditioned cells were also measured. In a third series of experiments, left ventricular biopsies of isolated rabbit hearts were obtained before and at selected times during 60 minutes of global ischemia, and the tissue was assayed for PP1 and PP2A activities. In isolated hearts pretreated with fostriecin, only 8% of the ischemic zone infarcted, significantly less than that in untreated control hearts (33%; P P P Conclusions —Fostriecin, a potent inhibitor of PP2A, can protect the rabbit heart from infarction even when administered after the onset of ischemia. But inhibition of either PP1 or PP2A does not appear to be the mechanism of protection from ischemic preconditioning.

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