Abstract 2693: Decreased Connexin43 Phosphorylation and Reduced Lateral Conduction Velocity Contribute to Arrhythmia Risk in Hypertrophic Cardiomyopathy Due to Troponin T Mutations
Carriers of the troponin T (TnT) I79N mutation linked to familial hypertrophic cardiomyopathy often die of sudden cardiac death at a young age. Mouse hearts expressing TnT-I79N are susceptible to reentrant ventricular tachycardia even without exhibiting interstitial fibrosis or hypertrophy. We hypothesized that slowed conduction due to altered regulation of the gap junction protein connexin 43 (C×43) contributes to the increased arrhythmia risk.
Methods: Optical activation maps (left ventricle stimulated at 10 Hz in the center of the field of view) were generated from isolated perfused control (n=20) and TnT-I79N (n=9) transgenic hearts. Fast (longitudinal) and slow (lateral) conduction velocity (CV) was calculated by plotting local CVs against orientation. After optical mapping, hearts were flash frozen and Cx43 phosphorylation analyzed by western blot. Phosphorylated Cx43 (P1, P2) migrated slower in SDS page and at least three distinct bands could be separated (P0, P1, P2).
Results: Lateral CV, but not the longitudinal CV, was significantly reduced in TnT-I79N mice compared to control (17.3±1.1 cm/s (n=5) vs. 25.3±2.7 cm/s (n=4) respectively, p<0.05). This decrease was associated with decreased expression of C×43 in TnT-I79N (to 67±4 % of control (n=12), p<0.01) and decreased Cx43 phosphorylation (un-phosphorylated P0-Cx43 increased to 146±20% of control, p<0.05). Blebbistatin, a Ca2+ desensitizer and contractile uncoupler, prevented ventricular arrhythmias in TnT-I79N hearts. Strikingly, blebbistatin also prevented both the decrease in lateral CV and Cx43 phosphorylation, while it had no effect in control hearts. Conversely, the Ca2+ sensitizer EMD57033, which mimics the Ca sensitizing effects of the TnT-I79N mutation, decreased Cx43 phosphorylation (P0-Cx43 491±147%, n=4, p<0.05) and lateral conduction velocity, and rendered control hearts susceptible to ventricular tachycardia induction.
Conclusion: Altered Cx43 phosphorylation leading to slowing of lateral CV likely represents one of the underlying mechanisms contributing to the arrhythmia susceptibility of TnT-I79N mice.
This research has received full or partial funding support from the American Heart Association, National Center.