Full-length article: Attenuation of mitochondrial, but not cytosolic, Ca super(2+) overload reduces myocardial injury induced by ischemia and reperfusion

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