Electrical Coupling and Propagation in Engineered Ventricular Myocardium With Heterogeneous Expression of Connexin43

Abstract

Rationale: Spatial heterogeneity in connexin (Cx) expression has been implicated in arrhythmogenesis. Objective: This study was performed to quantify the relation between the degree of heterogeneity in Cx43 expression and disturbances in electric propagation. Methods and Results: Cell pairs and strands composed of mixtures of Cx43 −/− (Cx43KO) or GFP-expressing Cx43 +/+ (WT GFP ) murine ventricular myocytes were patterned using microlithographic techniques. At the interface between pairs of WT GFP and Cx43KO cells, dual-voltage clamp showed a marked decrease in electric coupling (approximately 5% of WT) and voltage gating suggested the presence of mixed Cx43/Cx45 channels. Cx43 and Cx45 immunofluorescence signals were not detectable at this interface, probably because of markedly reduced gap junction size. Macroscopic propagation velocity, measured by multisite high-resolution optical mapping of transmembrane potential in strands of cells of mixed Cx43 genotype, decreased with an increasing proportion of Cx43KO cells in the strand. A marked decrease in conduction velocity was observed in strands composed of <50% WT cells. Propagation at the microscopic scale showed a high degree of dissociation between WT GFP and Cx43KO cells, but consistent excitation without development of propagation block. Conclusions: Heterogeneous ablation of Cx43 leads to a marked decrease in propagation velocity in tissue strands composed of <50% cells with WT Cx43 expression and marked dissociation of excitation at the cellular level. However, the small residual electric conductance between Cx43 and WT GFP myocytes assures excitation of Cx43 −/− cells. This explains the previously reported undisturbed contractility in tissues with spatially heterogeneous downregulation of Cx43 expression.