Abstract 16593: Flecainide and R-Propafenone Annihilate Calcium Waves in Calsequestrin Null Ventricular Myocytes By Decreasing the Number of Subcellular Calcium Wave Initiation Sites
Background- Mutations in the genes that encode either the ryanodine receptors (RyR2) or calsequestrin (casq2) can lead to catecholaminergic-polymorphic ventricular tachycardia (CPVT), a Ca2+-triggered arrhythmia. We recently reported that the RyR2 open-channel blockers flecainide (FLEC) and R-propafenone (RPROP) reduce spark mass and prevent Ca2+ waves in intact myocytes and CPVT in mice lacking calsequestrin (casq2-/-). We hypothesized that by decreasing spark mass FLEC and RPROP lead to a sub-threshold Ca2+ signal that reduces the likelihood of activating neighboring RyR2, thereby reducing the number of initiation sites and, thus, the generation of Ca2+ waves.
Methods and results- To test this hypothesis, we characterized the initiation sites in an experimental model of Ca2+ waves - permeabilized casq2-/- myocytes, and compared it against wild-type (WT) cells. We also quantified the effects of FLEC and RPROP on Ca2+ wave initiation sites in casq2-/- cells. Myocytes were imaged in 2D mode using confocal microscopy. Initiation sites were defined as the sites where the initial burst and fusion of sparks originates a propagated Ca2+ wave. Under control conditions ([EGTA]=0.05 mM, [Ca2+]t=0.06 mM), casq2-/- myocytes exhibit initiation sites ranged between 1 and 4 (2.3±0.1 (n=21)), localized at the ends as well as on the lateral sides of the cell. The simultaneous activation of various initiation sites determines the confluence of robust Ca2+ waves that enhances the propagation of the wave along the entire myocyte. In contrast, WT cells depict a significantly smaller number of initiation sites (between 1 and 2 (1.3±0.1 (n=15)). In WT the sites are localized predominantly at one end of the myocyte and their frequency of discharge is ~ 40 % lower compared to casq2-/-. When casq2-/- cells are exposed either FLEC (25 µM) or RPROP (25 µM) the number of initiation sites significantly decreased to approximately 60% of control values (FLEC=1.3±0.1 (n=15), RPROP=1.4±0.1 (n=9), p<0.01).
Conclusion- The data presented here suggest that the decrease in the number of initiation sites is an underlying mechanism responsible for the annihilation of Ca2+ waves by FLEC or RPROP and, thus, for preventing delayed-after-depolarizations and ventricular arrhythmias.
- Arrhythmias, treatment of
- Ventricular arrhythmia
- Excitation-contraction coupling (ECC)
- © 2011 by American Heart Association, Inc.