Pharmacological Modulation of Mitochondria Ca2+ Exerts Divergent Effects on Arrhythmogenic Calcium Waves in Ca2+-Dependent and Metabolic Cardiac Disease

Abstract

matching mitochondrial ATP production to the myocyte's energetic requirements. Here we tested whether elevated activity of RyR2 resulted in selfimposed exacerbation of SR Ca 2þ leak, via altered SR-mitochondrial Ca 2þ transfer and increased mito-ROS emission. In ventricular myocytes from rats and catecholaminergic polymorphic ventricular tachycardia (CPVT) mice, fluorescent indicators and organelle-targeted redox biosensors revealed that pharmacologically and genetically enhanced RyR2 activity led to elevated ROS emission during b-adrenergic stimulation. Mitochondrial-targeted Ca 2þ biosensor mtRCamp1h showed that mitochondria has a reduced ability to uptake and accumulate Ca 2þ . Voltage-sensitive dye TMRM revealed this was due to depolarization of the mitochondrial matrix. Although this offers protection against deleterious mitochondrial Ca 2þ overload, mito-ROS emission was significantly increased by enhanced SR Ca 2þ leak and resulted in RyR2 oxidation, thus exacerbating augmented channel activity. Application of mito-ROS scavenger mitoTEMPO attenuated the effects of increased RyR2 Ca 2þ release, reducing the incidence of proarrhythmic spontaneous Ca 2þ waves. Furthermore, the hypothesis that transfer of Ca 2þ from the SR to mitochondria is essential to mito-ROS emission was supported by experiments with dominant-negative paralog of the mitochondrial Ca 2þ uniporter (MCU), whereby it was reduced by inhibition of mitochondrial Ca 2þ uptake. These findings suggest that in a detrimental feedback cycle, hyperactivity of RyR2 channels and SR-mitochondrial Ca 2þ transfer results in increased channel oxidation via mito-ROS. Increased leak therefore induces leak, further augmenting proarrhythmic SR Ca 2þ release in diseased myocytes.