Propafenone-mediated gap junctional uncoupling results from aberrant connexin-43 trafficking

Connexin-43 (Cx43) is the principal gap junction protein in the heart, mediating electrical coupling and ion exchange between cardiomyocytes to maintain synchronous contraction. Any disruption or malfunction of Cx43 can lead to arrhythmias and other cardiac issues. Understanding the functions and regulation of Cx43 is vital in both basic research and clinical contexts. Propafenone, a class Ic antiarrhythmic drug, has shown promise in rhythm control; however, its precise impact on cardiac cellular physiology, particularly regarding Cx43, remains incompletely understood. The present study investigated propafenone’s effects on Cx43 protein content, physiology, and underlying mechanisms in cell systems. Cell lines include human embryonic kidney HEK293 cells transfected with Cx43 (Ex-HEK); differentiated murine embryonic carcinoma EPI7 cells with an epithelioid morphology and visceral endoderm-like END2 cells, both endogenously expressing functional Cx43. Cx43 protein contents were determined by Western blot analysis, whereas immunofluorescence (IF) imaging was used to assess the subcellular localization of Cx43 proteins. Dye injections were used to gain insight into the effects of propafenone on Cx43 function. Full-length Cx43 protein levels were dose-dependently increased after propafenone treatment and IF microscopy showed an intracellular accumulation of Cx43 protein, both on heterologously and endogenously expressed Cx43. Propafenone did not alter the Cx43 half-life, in contrast to the lysosomal inhibitor chloroquine. Finally, gap-junctional coupling was decreased by chronic propafenone treatment. We conclude that propafenone increases non-functional Cx43 protein content, resulting in its intracellular accumulation, as a side effect.