Attenuation of mitochondrial, but not cytosolic, Ca2+ overload reduces myocardial injury induced by ischemia and reperfusion

Aim: Attenuation of mitochondrial Ca2+ ([Ca2+](m)), but not cytosolic Ca2+ ([Ca2+](c)), overload improves contractile recovery. We hypothesized that attenuation of [Ca2+](m), but not [Ca2+](c), overload confers cardioprotection against ischemia/ reperfusion-induced injury. Methods: Infarct size from isolated perfused rat heart, cell viability, and electrically-induced Ca2+ transient in isolated rat ventricular myocytes were measured. We determined the effects of BAPTA-AM, a Ca2+ chelator, at concentrations that abolish the overload of both [Ca2+](c) and [Ca2+](m), and ruthenium red, an inhibitor of mitochondrial uniporter of Ca2+ transport, at concentrations that abolish the overload of [Ca2+](m), but not [Ca2+](c), on cardiac injury induced by ischemia/reperfusion. Results: Attenuation of both [Ca2+](m) and [Ca2+](c) by BAPTA-AM, and attenuation of [Ca2+](m), but not [Ca2+](c), overload by ruthenium red, reduced the cardiac injury observations, indicating the importance of [Ca2+](m) in cardioprotection and contractile recovery in response to ischemia/reperfusion. Conclusion: The study has provided unequivocal evidence using a cause-effect approach that attenuation of [Ca2+](m), but not [Ca2+](c), overload is responsible for cardioprotection against ischemia/reperfusion-induced injury. We also confirmed the previous observation that attenuation of [Ca2+](m), but not [Ca2+](c), by ruthenium red improves contractile recovery following ischemia/ reperfusion.