Mitochondrial Ca 2+ overload is a pivotal risk factor for lethal ventricular arrhythmias due to the oxidation of mitochondrial respirasome and energetic failure

Background and Purpose Ventricular arrhythmias are a leading cause of death among patients with cardiovascular diseases and are associated with elevated levels of catecholamines. Mitochondrial Ca 2+ transport is essential for initiating an adrenergic response. However, continuous stimulation might lead to mitochondrial Ca 2+ overload and dysfunction within cardiac tissue. This study investigates the role of mitochondrial Ca 2+ in lethal arrhythmogenesis and the effects of its modulation. Experimental Approach Male C57BL/6 mice were administered either Ru360 (oxo‐bridged dinuclear ruthenium ammine complex) a potent and selective mitochondrial Ca 2+ transport inhibitor, or normal saline via intravenous injection. A baseline electrocardiogram (ECG) was recorded, followed by subcutaneous administration of isoprenaline. The ECG was monitored for an additional 20 min, after which cardiomyocytes and mitochondria were isolated for further characterization studies. Key Results Isoprenaline administration led to ventricular tachycardia and fibrillation, but Ru360 pretreatment successfully prevented these arrhythmias. Mitochondria from isoprenaline‐treated hearts showed higher Ca 2+ content, indicating overload that compromised mitochondrial function and membrane integrity, evidenced by decreased respiratory control, reduced Ca 2+ retention capacity and diminished membrane potential. Isoprenaline also increased oxidative stress, illustrated by elevated peroxide production, electron leak and acute oxidative modifications, and erratic cellular Ca 2+ dynamics. This mitochondrial dysfunction correlated with a decreased respirasome activity, but not a difference in respirasome abundance quantified by complexome profiling, which was prevented by Ru360 pretreatment. Conclusion Mitochondrial Ca 2+ overload significantly contributes to arrhythmias by disrupting respirasome function and increasing oxidative stress, impairing cellular Ca 2+ dynamics. Modulating mitochondrial Ca 2+ transport might be a promising strategy for developing innovative antiarrhythmic therapies.