Elucidation of molecular mechanism and treatment for abnormal ryanodine receptor in patients with malignant hyperthermia and lethal arrhythmia

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The N-terminal (1-600) and central (2000-2500) domains of the ryanodine receptor (RyR), harbor many mutations associated with malignant hyperthermia (MH), catecholaminergic polymorphic ventricular tachycardia (CPVT), and arrhythmogenic right ventricular cardiomyopathy type 2. There is strong evidence to suggest that inter-domain interaction between these regions plays an important role in the mechanism of channel regulation. Recently we reported that dantrolene, a specific drug for the treatment of MH, prevented abnormal Ca^<2+> leak by the correction of the defective inter-domain interaction between N-terminal and central domains within MU RyRI. Here, we examined the effect of dantrolene on the Ca^<2+> release function of RyR2 in human CPVT-associated RyR2^<R24745/+> knock-in (KI) mice model.To identify the dantrolene-binding region we screened several recombinant fragments (-600 amino acid residues) corresponding to various regions covering the area from the N-terminus to residue 275 … More 0, which include the aforementioned mutable domains. Dantrolene was found to specifically bind to the domain 601-620 of RyR2 using a quartz crystal microbalance technique (a highly sensitive mass-measuring technique). ECG was monitored in KI mice (n=6) and wild-type (WT) mice (n=6), before and after injection of epinephrine (1.0 mg/kg) or exercise by treadmill. In KI mice bi-directional ventricular tachycardia (VT) was easily induced after injection of epinephrine or exercise, but not in WT mice. In K1 mice pretreated with dantrolene for 7 days, number of premature ventricular contractions at rest significantly decreased, and VT was not induced by injection of epinephrine or exercise. In cardiomyocytes from KI mice, Ca^<2+> spark (SpF; s^<-1>・100μm^<-1>:15.8±0.6, p<0.01) and delayed afterdepolarization-mediated Ca^<2+> transient (DAD-CaT) were frequently seen after addition of isoproterenol, compared to those from WT mice (SpF: 0.8±0.1). Both SpF and DAD-CaT seen in KI mice were inhibited by 1.0 μM dantrolene (SpF: 1.5±0.2, p<0.01).In cardiomyocytes from KI mice, Ca' spark (SpF ; s1900prif 15.8±0.6, p<0.01) and delayed afterdepolarization-mediated Ca' transient(DAD-CaT) were frequently seen after addition of isoproterenol, compared to those from WT mice (SpF : 0.8±0.1). Both SpF and DAD-CaT seen in KI mice were inhibited by 1.0 p.M dantrolene (SpF : I.5±0.2, p<0.01). n conclusion, dantrolene, by interacting with N-terminal mutable domain, seems to correct the hypersensitized channel gating caused by RyR2 mutation, thereby inhibiting diastolic Ca^<2+> sparks, DAD, and then lethal arrhythmia. Less