Abstract 15775: Tachycardia Rapidly Induces Regional Changes in Gap Junctions and Generates a Substrate for Re-entry Arrhythmias in Myofilament Ca2+ Sensitized Hearts
Increased myofilament Ca2+ sensitivity, a common finding in hypertrophic cardiomyopathy (HCM), is associated with an increased susceptibility for arrhythmias. Reentry-type arrhythmias are induced by injection of Isoproterenol (Iso) and ex vivo by fast pacing of isolated perfused hearts expressing a Ca sensitizing troponin T (TnT-I79N) HCM mutation. Fast pacing also triggers arrhythmias in control hearts after application of the Ca2+ sensitizer EMD57033. Regional conduction velocity (CV) slowing may contribute to formation of the arrhythmogenic substrate, but the underlying mechanism has not been elucidated. In the absence of structural abnormalities we hypothesized that a change in intercellular coupling via gap junctions (GJ) is responsible. Optical mapping studies revealed a slower lateral CV and increased anisotropy (fast/slow CV) in TnT-I79N and EMD treated hearts compared to control (all groups n≥7, p<0.05), consistent with changes in GJ conductance. We then analyzed connexin 43 (Cx43) by Western blot in total and soluble heart tissue fractions (three isoforms were separated (P0,P1,P2)), and via confocal imaging of immunostained frozen heart sections. No difference was detectable under baseline conditions in Cx43 expression level, soluble/insoluble ratio and isoform distribution in all assays (all n≥7). However, after hearts were rapidly paced (12-18 Hz for 16 min) Cx43 expression was lower in TnT-I79N compared to control (64.8±6.6%, n≥7, p=0.03) and the P0/P2 ratio increased (p=0.01). Strikingly, areas with high accumulation of Cx43-P0 isoform (“clusters”) were detected, with little homogeneous staining in controls. The P0/P2 ratio shift and the occurrence of P0 clusters were both prevented by the Ca de-sensitizer/uncoupler blebbistatin, which simultaneously suppressed the arrhythmias. Importantly, P0 clusters were also observed in EMD treated controls and in TnT-I79N mice after Iso injection in vivo (larger stdev for P0, both p≤0.05). We conclude that these rapidly induced clusters of Cx43-P0 may be responsible for the regional slowing of CV and thus formation of the arrhythmogenic substrate in Ca sensitized hearts. This constitutes a novel mechanism that increases susceptibility for reentry arrhythmias within minutes.
- © 2011 by American Heart Association, Inc.