Abstract 13377: Modulating Mitochondrial Phosphate Transport Shapes Intracellular Ca Signaling to Impact Arrhythmogenesis

Abstract

Introduction: Catecholaminergic polymorphic ventricular tachycardia (CPVT) is a stress-induced arrhythmic syndrome due to genetic defects of the sarcoplasmic reticulum (SR) Ca release channel complex of ryanodine receptor 2 (RyR2). Our recent study suggests that mitochondria function as a Ca buffer to absorb RyR2-mediated aberrant Ca release and thus mitigate its detrimental consequences in CPVT. Mitochondrial phosphate (Pi) transport has been shown to play a role in both mitochondrial Ca uptake and buffering. Hypothesis: We hypothesize that modulating mitochondrial Pi transport impacts arrhythmogenesis in CPVT by altering mitochondrial Ca uptake and buffering. Methods: Ventricular myocytes were isolated from a genetic CPVT model of CASQ2 knockout (Cnull) mouse. Fluorescent imaging experiments were performed with live cells to examine intracellular Ca dynamics and cellular arrhythmic burden. Mitochondrial Pi transport was modulated by a pharmacological inhibitor or manipulating cytosolic Pi concentration. Results: In the presence of β agonist isoproterenol, an inhibitor of mitochondrial Pi carrier N-ethylmaleimide (NEM) significantly exacerbated Ca handling of intact Cnull cells, resulting in more than 60% of cells displaying pacing-independent Ca oscillations. The NEM treatment also significantly increased the amplitude of cytosolic Ca transient and SR Ca content. Consistent with results obtained in intact cells, NEM treatment exacerbated arrhythmogenic Ca waves and reduced mitochondrial Ca uptake in permeabilized Cnull cells. Moreover, inhibiting mitochondrial Pi transport by lowering cytosolic Pi concentration also increased the frequency of Ca waves and reduced mitochondria Ca uptake in permeabilized Cnull cells. On the contrary, increasing cytosolic Pi concentration reduced the frequency of Ca waves and increased mitochondrial Ca uptake in permeabilized Cnull cells. Conclusions: Modulating mitochondrial Pi transport impacts arrhythmogenesis in CPVT cells through altering mitochondrial Ca uptake and buffering. Enhancing mitochondrial Pi transport may represent a promising therapeutic strategy to reduce arrhythmogenic Ca waves and cardiac arrhythmias in CPVT.