Abstract 798: Ca 2+ Sparks are Modulated by the Mitochondrial Energy State

Abstract

Mitochondria produce reactive oxygen species (ROS) but are also a target of oxidative stress that can induce rapid oscillations of mitochondrial inner membrane potential (ΔΨ m ). The proximity of mitochondria to SR Ca 2+ release sites suggests that the mitochondrial energy state will determine the local redox and energetic status of the Ca 2+ handling subsystem. Because ryanodine receptors, SERCA, and L-type Ca 2+ channels are all sensitive to ATP, Mg 2+ and thiol oxidation, we investigated whether laser flash-triggered mitochondrial ΔΨ m oscillations influence resting Ca 2+ spark frequency in fluo-4 + TMRE-loaded cardiomyocytes using two-photon microscopy to monitorΔΨ m , cytosolic [Ca 2+ ], and [NADH]. The correlation between resting Ca 2+ spark frequency and ΔΨ m was analyzed over several cycles of ΔΨ m oscillation in each cell. Notably, Ca 2+ spark frequency increased with ΔΨ m depolarization and decreased withΔΨ m repolarization, indicative of close coupling between energetics and Ca 2+ cycling (See Figure ). Moreover, spontaneous Ca 2+ waves were often observed when mitochondria were depolarized but not whenΔΨ m recovered. There were no significant effects on Ca 2+ spark durations or rise times. In conclusion, the results show that stress-induced mitochondrial depolarization (involving NADH oxidation, ROS release, and depletion of glutathione) leads to increased Ca 2+ spark frequency, most likely as a result of modification of the local redox status near the dyad. These findings provide important insights into the connection between metabolism and Ca 2+ cycling in the heart with relevance to the mechanism of contractile and electrical dysfunction in cardiac disease states.