Background— Connexin 43 (Cx43) is a major determinant of conduction in the ventricular working myocardium of mammals. We investigated the effect of decreased Cx43 expression on conduction velocity and arrhythmogenesis using adult mice with inducible deletion of Cx43.

Methods and Results— Cx43^Cre-ER(T)/+ mice, in which 1 coding region of the Cx43 gene was replaced by Cre-ER(T), were mated to Cx43^fl/fl mice, generating Cx43^Cre-ER(T)/fl mice. Application of 4-hydroxytamoxifen (4-OHT) induced Cre-ER(T)–mediated deletion of the floxed Cx43 allele. Epicardial ventricular mapping using a 13×19 multiterminal electrode grid (300-μm spacing) was performed on Langendorff-perfused hearts from Cx43^fl/fl plus carrier (n=10), Cx43^fl/fl plus 4-OHT (n=10), Cx43 ^Cre-ER(T)/fl plus carrier (n=9), and Cx43^Cre-ER(T)/fl plus 4-OHT (n=10). Cx43 protein amount in group 3 hearts was decreased by ≈50% compared with group 1. 4-OHT did not affect cardiac protein amounts in group 2 but decreased Cx43 expression up to 95% in group 4 compared with group 3. Epicardial activation of both left ventricle (LV) and right ventricle (RV) during sinus rhythm was similar in all groups. Conduction velocity (CV) changed only in group 4 animals. For RV (LV), longitudinal CV decreased from 38 (35) to 31.6 (33.6) and transverse CV from 24.4 (16.8) to 10.1 (11.3) cm/s. Dispersion of conduction in RV (LV) was increased by 91% (38%). Programmed stimulation resulted in ventricular arrhythmias in group 4 (7 of 10 mice) but never in groups 1 through 3.

Conclusions— Heterozygous expression of Cx43 did not affect ventricular conduction velocity. Up to 95% decrease of Cx43 protein in 4-OHT–treated Cx43^Cre-ER(T)/fl mice reduced conduction velocity and increased dispersion of conduction and propensity for ventricular arrhythmias.