Macrophage-Dependent Interleukin-6-Production and Inhibition of I(K) Contributes to Acquired QT Prolongation in Lipotoxic Guinea Pig Heart

In the heart, the delayed rectifier K current, I(K), composed of the rapid (I(Kr)) and slow (I(Ks)) components contributes prominently to normal cardiac repolarization. In lipotoxicity, chronic elevation of pro-inflammatory cytokines may remodel I(K), elevating the risk for ventricular arrythmias and sudden cardiac death. We investigated whether and how the pro-inflammatory interleukin-6 altered I(K) in the heart, using electrophysiology to evaluate changes in I(K) in adult guinea pig ventricular myocytes. We found that palmitic acid (a potent inducer of lipotoxicity), induced a rapid (~24 h) and significant increase in IL-6 in RAW264.7 cells. PA-diet fed guinea pigs displayed a severely prolonged QT interval when compared to low-fat diet fed controls. Exposure to isoproterenol induced torsade de pointes, and ventricular fibrillation in lipotoxic guinea pigs. Pre-exposure to IL-6 with the soluble IL-6 receptor produced a profound depression of I(Kr) and I(Ks) densities, prolonged action potential duration, and impaired mitochondrial ATP production. Only with the inhibition of I(Kr) did a proarrhythmic phenotype of I(Ks) depression emerge, manifested as a further prolongation of action potential duration and QT interval. Our data offer unique mechanistic insights with implications for pathological QT interval in patients and vulnerability to fatal arrhythmias.