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

Abstract

Spatial heterogeneity in connexin (Cx) expression has been implicated in arrhythmogenesis. This study was performed to quantify the relation between the degree of heterogeneity in Cx43 expression and disturbances in electric propagation. 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. 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.