Ryanodine Receptor Use-Dependent Block Suppresses Ca2+ Waves in Permeabilized Casq2-/- and RyR2-R4496C Myocytes

Abstract

Background-Casq2 and RyR2 mutations can both cause catecholaminergic-polymorphic ventricular tachycardia (CPVT). Leaky RyR2s (increased open probability) generate Ca2+ waves, delayed afterdepolarizations and ventricular arrhythmias. We hypothesize that the RyR2 open-state inhibitors flecainide (FLEC) and R-propafenone (RPROP) abolish this sequence of events in both CPVT genotypes.Methods and Results-Using confocal microscopy, we recorded Ca2+ waves in permeabilized myocytes from casq2-/-, RyR2-R4496C and wild-type (WT) mice. Casq2-/- myocytes showed the highest wave frequency and speed and the lowest amplitude, RyR2-R4496C exhibited intermediate values and WT had the lowest values (Figure). We next obtained FLEC and RPROP concentration-response curves and calculated IC50 and efficacy of wave inhibition. Both FLEC and RPROP reduced all wave parameters with higher potency (lower IC50) and efficacy in casq2-/- and RyR4496C compared to WT (FLEC: IC50 12μM vs 22μM vs 49μM; efficacy 43% vs 29% vs 21% for casq2-/-, RyR2-R4496C and WT respectively. RPROP: IC50 18μM vs 28μM; efficacy 36% vs 17% for RyR2-R4496C and WT respectively; n=10-60 cells per group).Conclusion-RyR2 activity determines the potency and efficacy of open-state blockers for suppressing arrhythmogenic Ca2+ waves in permeabilized myocytes from casq2-/- and RyR2-R4496C CPVT models.View Large Image | View Hi-Res Image | Download PowerPoint Slide