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.