Scavenging free radicals by low-dose carvedilol prevents redox-dependent Ca2+ leak via stabilization of ryanodine receptor in heart failure.

We investigated whether defective intracellular Ca2+ handling is corrected by carvedilol in heart failure. In heart failure, the interaction between the N-terminal and central domains of the ryanodine receptor (RyR), the domains where many mutations have been found in patients with catecholaminergic polymorphic ventricular tachycardia (CPVT), is defective, as shown in our recent report. Sarcoplasmic reticulum vesicles were isolated from canine left ventricular muscle (normal or 4-weeks rapid ventricular pacing). The RyR was labeled with the fluorescent conformational probe methylcoumarin acetate (MCA) with DPc10 (a synthetic peptide corresponding to Gly2460-Pro2495 of RyR, one of the mutable domains in CPVT) as a site-direction carrier. Normal cardiac function was well preserved in carvedilol-treated/paced dogs (CV+) but not in the untreated/paced dogs (CV-). In CV-, the interdomain interaction within RyR was defective (i.e., in an unzipped state), as determined by the fluorescence quenching technique. However, in CV+, the domain interaction remained normal (i.e., in a zipped state). In CV-, oxidative stress of RyR (reduction in the number of free thiols) was severe, but it was negligible in CV+. In (CV-) failing cardiomyocytes, incubation with low-dose CV (30 nmol/l), which eliminated intracellular reactive oxygen species with no acute effect on cell shortening, markedly improved the contractile function and Ca2+ transient. However, after domain unzipping by DPc10, CV was without effect. Carvedilol, at a concentration that is sufficient to produce antioxidant effect, improves the intracellular Ca2+ handling and contractile dysfunction by correcting defective interdomain interaction within the RyR in the failing heart.