Abstract 17691: Local Na+/Ca2+ Signaling Contributes to the Propensity for Arrhythmogenic Spontanous Ca2+ Waves During Catecholaminergic Polymorphic Ventricular Tachycardia (CPVT)
Background: Na+ channel inhibitors prevent arrhythmias in catecholaminergic polymorphic ventricular tachycardia (CPVT), but their antiarrhythmic mechanism remains elusive. Previously, it has been proposed that these agents reduce CPVT by affecting the cardiac ryanodine receptor (RyR2) directly and/or by modulating cellular excitability. However, the role of local Na+/Ca2+ signaling in CPVT is poorly understood and is the focus of this research.
Methods: After-contractions were monitored in Casq2-R33Q isolated trabeculae, while confocal microscopy of wild type (WT) and Casq2-R33Q isolated murine ventricular myocytes and trabeculae was used to assess Ca2+ handling during various pharmacological interventions.
Results: In R33Q trabeculae, 0.1-1μ M tetrodotoxin (TTX) decreased frequency of isoproterenol (ISO, 10-300nM) induced after-contractions in a concentration dependent manner. Confocal microscopy of these preparations revealed that direct modulation of spontaneous Ca2+ waves (SCWs) by TTX was primarily responsible for this phenomenon. Likewise, application of 100nM TTX to ISO (100nM) treated R33Q myocytes decreased frequency of SCWs by 66.1±24.0% and increased the latency by 81.6±8.1% without affecting either the Ca2+ transient amplitude or sarcoplasmic reticulum (SR) Ca2+ load. Interestingly, in quiescent, ISO treated R33Q myocytes TTX decreased Ca2+ spark frequency(by 12.2±9.7%) and amplitude (by 14.3±10.6%) without altering SR Ca2+ load suggesting a direct involvement of local Na+/Ca2+ signaling on SCWs. This assertion was further supported in quiescent, WT mycytes by an increase in both Ca2+ spark frequency (by 35.8±8.8%) and amplitude (by 18.7±9.3%) and reduced SR Ca2+ load (by 17.5±6.5%) during neuronal Na+ current augmentation with β-pompilidotoxin (β-PMTX, 50μ M). Importantly, effects of β-PMTX on spark parameters were reversed by Na+/Ca2+ exchange inhibition with 5μ M SN-6. Further, SCW frequency in WT, ISO treated myocytes during β-PMTX application was increased by 31.8±11.3%, while decreasing SR Ca2+ load.
Conclusion: These data suggest that a local Na+/Ca2+ signaling independent of SR Ca2+ load, direct RyR2 inhibition or reduced excitability, contribute to propensity for arrhythmogenic SCWs during CPVT.
- © 2012 by American Heart Association, Inc.