The Antiarrhythmic Effect of Inhibition of the Mitochondrial Calcium Uniporter under Catecholamine Overload is Partly Dependent on Mitochondrial Function Preservation

Abstract

IntroductionVentricular arrhythmias are a major cause of mortality in cardiovascular patients. Catecholamines have been associated with the development of ventricular arrhythmias and no new intervention has demonstrated efficacy in reducing mortality since the use of β‐blockers. Mitochondrial calcium transport has been deemed necessary for an adequate adrenergic response and constant adrenergic stimulation leads to mitochondrial calcium overload with subsequent mitochondrial dysfunction. Inhibition of the mitochondrial calcium uniporter (MCU) have been described to reduce asynchronized contraction in cellular and animal models. In this study, we assessed the effects that MCU inhibition by administration of Ru360, a MCU inhibitor, has on ventricular arrhythmia incidence in a model of catecholamine toxicity and characterize cellular and mitochondrial function to describe the subcellular mechanisms involved.MethodsThe study followed the national guidelines for laboratory animal use and care and was approved by the Animal Care and Use Committee. 12‐15‐week‐old C57bl/6 male mice received Ru360 or normal saline via IV, and a baseline ECG was recorded. Afterwards, Isoproterenol (400mg/kg) was administrated subcutaneously, and ECG recording was kept for another 20 minutes. Finally, hearts were excised, and cardiomyocytes and mitochondria isolated for further characterization. Data is presented as mean ± SEM. Fisher exact test was performed to evaluate arrhythmia incidence and one‐way ANOVA followed by Holm‐Sidak method for mitochondrial experiments and heart rate measurements.ResultsRu360 completely prevented the development of ventricular arrhythmias at a dose of 50nmol/kg. Mitochondrial Ca2+ transport inhibition preserved mitochondrial function and membrane integrity demonstrated by a preserved respiratory control and calcium retention capacity and a partially preserved mitochondrial membrane potential. MCU inhibition also prevented mitochondrial membrane potential loss upon the addition of a Ca2+ insult. The effects shown appear to be caused by a reduced oxidative stress, shown by a higher cytochrome c oxidase activity, that helps preserve cellular Ca2+ homeostasis as seen in confocal microscopy.ConclusionRu360 prevents arrhythmias possibly by reducing mitochondrial Ca2+ overload, preserving mitochondrial function, preventing mitochondrial ROS formation and oxidative damage, and conserving cellular Ca2+ homeostasis.