Abstract
β-Adrenergic receptor (β-AR) activation produces the main positive inotropic response of the heart. During ischemia-reperfusion (I/R), however, β-AR activation can trigger life-threatening arrhythmias. Because I/R is frequently associated with oxidative stress, we investigated whether ryanodine receptor (RyR) oxidation contributes to proarrythmogenic Ca2+ waves during β-AR activation. Measurements of contractile and electrical activity from Langendorff-perfused rabbit hearts revealed that I/R produces tachyarrhythmias. Ventricular myocytes isolated from I/R hearts had an increased level of oxidized glutathione (i.e., oxidative stress) and a decreased level of free thiols in RyRs (i.e., RyR oxidation). Furthermore, myocytes from I/R hearts were characterized by increased sarcoplasmic reticulum (SR) Ca2+ leak and enhanced fractional SR Ca2+ release. In myocytes from nonischemic hearts, β-AR activation with isoproterenol (10 nM) produced only a positive inotropic effect, whereas in myocytes from ischemic hearts, isoproterenol at the same concentration triggered spontaneous Ca2+ waves. β-AR activation produced a similar effect on RyR phosphorylation in control and I/R myocytes. Treatment of myocytes from I/R hearts with the reducing agent mercaptopropionylglycine (100 μM) attenuated RyR oxidization and decreased Ca2+ wave frequency during β-AR activation. On the other hand, treatment of myocytes from nonischemic hearts with H2O2 (50 μM) increased SR Ca2+ leak and triggered Ca2+ waves during β-AR activation. Collectively, these results suggest that RyR oxidation after I/R plays a critical role in the transition from positive inotropic to arrhythmogenic effects during β-AR stimulation. Prevention of RyR oxidation can be a promising strategy to inhibit arrhythmias and preserve positive inotropic effect of β-AR activation during myocardial infarction. NEW & NOTEWORTHY Oxidative stress induced by ischemia plays a critical role in triggering arrhythmias during adrenergic stimulation. The combined increase in sarcoplasmic reticulum Ca2+ leak (because of ryanodine receptor oxidation) and sarcoplasmic reticulum Ca2+ load (because of adrenergic stimulation) can trigger proarrythmogenic Ca2+ waves. Restoring normal ryanodine receptor redox status can be a promising strategy to prevent arrhythmias and preserve positive inotropic effect of adrenergic stimulation during myocardial infarction.