Restoration of mitochondrial Ca2+ and redox homeostasis by enhancement of SK channels rescues Ca2+ cycling in HFpEF cardiomyocytes.

Heart failure with preserved ejection fraction (HFpEF) accounts for nearly half of all heart failure cases. In addition to diastolic dysfunction, patients with HFpEF have a substantial risk of sudden cardiac death, suggesting a potential contribution of malignant ventricular arrhythmias. Recently, small conductance Ca2+-activated K+ (SK) channels have emerged as potential modulators of mitochondria-dependent production of harmful reactive oxygen species (ROS). This study aimed to evaluate SK channel enhancement as a novel strategy to reverse proarrhythmic changes in intracellular Ca2+ cycling and in mitochondrial redox and Ca2+ homeostasis in ventricular myocytes using obese ZSF1 rat model of HFpEF. Confocal imaging of Ca2+ and ROS was performed in ventricular myocytes isolated from lean and obese ZSF1 rats. Mitochondrial matrix Ca2+ and ROS levels were measured using matrix-targeted biosensors mtRCamp1h and MLS-HyPer7, respectively. SK channel activity was enhanced by adenoviral overexpression of rat SK channel type 2 and by pharmacological activators NS309 and Riluzole. Ventricular myocytes from obese ZSF1 rats, when periodically paced and exposed to the β-adrenergic agonist isoproterenol, showed increased pro-arrhythmic diastolic sarcoplasmic reticulum (SR) Ca2+ release, elevated mitochondrial ROS production, and marked mitochondrial Ca2+ overload. SK channel enhancement prevented mitochondrial Ca2+ overload, reduced ROS emission, and improved cytosolic Ca2+ cycling by suppressing diastolic SR Ca2+ release These findings identify SK channel activation as a potential antiarrhythmic therapeutic strategy in HFpEF by limiting mitochondrial Ca2+ uptake, reducing oxidative stress and stabilizing intracellular Ca2+ dynamics.