Dantrolene, a Therapeutic Agent for Malignant Hyperthermia, Markedly Improves the Function of Failing Cardiomyocytes by Stabilizing Interdomain Interactions Within the Ryanodine Receptor

Objectives We sought to investigate the effect of dantrolene, a drug generally used to treat malignant hyperthermia, on the Ca(2+) release and cardiomyocyte function in failing hearts. Background The N-terminal (N: 1-600) and central (C: 2000-2500) domains of the ryanodine receptor (RyR) harbor many mutations associated with malignant hyperthermia in skeletal muscle RyR (RyR1) and polymorphic ventricular tachycardia in cardiac RyR (RyR2). There is strong evidence that interdomain interaction between these regions plays an important role in the mechanism of channel regulation. Methods Sarcoplasmic reticulum vesicles and cardiomyocytes were isolated from the left ventricular muscles of dogs (normal or rapid ventricular pacing for 4 weeks), for Ca(2+) leak, transient, and spark assays. To assess the zipped or unzipped state of the interacting domains, the RyR was labeled fluorescently with methylcoumarin acetate in a site-directed manner. We used a quartz-crystal microbalance technique to identify the dantrolene binding site within the RyR2. Results Dantrolene specifically bound to domain 601-620 in RyR2. In the sarcoplasmic reticulum isolated from pacing-induced failing dog hearts, the defective interdomain interaction (domain unzipping) had already occurred, causing spontaneous Ca(2+) leak. Dantrolene suppressed both domain unzipping and the Ca(2+) leak, demonstrating identical drug concentration-dependence (IC(50) = 0.3 mu mol/l). In failing cardiomyocytes, both diastolic Ca(2+) sparks and delayed afterdepolarization were observed frequently, but 1 mu mol/l dantrolene inhibited both events. Conclusions Dantrolene corrects defective interdomain interactions within RyR2 in failing hearts, inhibits spontaneous Ca(2+) leak, and in turn improves cardiomyocyte function in failing hearts. Thus, dantrolene may have a potential to treat heart failure, specifically targeting the RyR2. (J Am Coll Cardiol 2009; 53: 1993-2005) (C) 2009 by the American College of Cardiology Foundation