Attenuation of mitochondrial, but not cytosolic, Ca^2＋ overload reduces myocardial injury induced by ischemia and reperfusion

Aim： Attenuation of mitochondrial Ca^2＋ （[Ca^2＋]m）, but not cytosolic Ca^2＋ （[Ca^2＋]c）, overload improves contractile recovery. We hypothesized that attenuation of [Ca^2＋]m, but not [Ca^2＋]c overload confers cardioprotection against ischemia/ reperfusion-induced injury. Methods： Infarct size from isolated perfused rat heart, cell viability, and electrically-induced Ca^2＋ transient in isolated rat ventricular myocytes were measured. We determined the effects of BAPTA-AM, a Ca^2＋ chelator, at concentrations that abolish the overload of both [Ca^2＋]c and [Ca^2＋]m, and ruthenium red, an inhibitor of mitochondrial uniporter of Ca^2＋ transport, at concentrations that abolish the overload of [Ca^2＋]m, but not [Ca^2＋]c on cardiac injury induced by ischemia/reperfusion. Results： Attenuation of both [Ca^2＋]m and [Ca^2＋]c by BAPTA-AM, and attenuation of [Ca^2＋]m, but not [Ca^2＋]c, overload by ruthenium red, reduced the cardiac injury observations, indicating the importance of [Ca^2＋]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 [Ca^2＋]m, but not [Ca^2＋]c, overload is responsible for cardioprotection against ischemia/reperfusion-induced injury. We also confirmed the previous observation that attenuation of [Ca^2＋]m, but not [Ca^2＋]c, by ruthenium red improves contractile recovery following ischemia/ reperfusion.