Cx43 hemichannel microdomain signaling at the intercalated disc enhances cardiac excitability.

Abstract

Cx43, a major cardiac connexin, forms precursor hemichannels that accrue at the intercalated disc to assemble as gap junctions. While gap junctions are crucial for electrical conduction in the heart, little is known on potential roles of hemichannels. Recent evidence suggests that inhibiting Cx43 hemichannel opening with Gap19 has antiarrhythmic effects. Here, we used multiple electrophysiology, imaging and super-resolution techniques to understand and define the conditions underlying Cx43 hemichannel activation in ventricular cardiomyocytes, their contribution to diastolic Ca2+ release from the sarcoplasmic reticulum, and their impact on electrical stability. We showed that Cx43 hemichannels are activated during diastolic Ca2+ release in single ventricular cardiomyocytes and cardiomyocyte cell pairs from mouse and pig. This activation involved Cx43 hemichannel Ca2+ entry and coupling to Ca2+ release microdomains at the intercalated disc resulting in enhanced Ca2+ dynamics. Hemichannel opening furthermore contributed to delayed afterdepolarizations and triggered action potentials. In single cardiomyocytes, cardiomyocyte cell pairs and arterially perfused tissue wedges from failing human hearts, increased hemichannel activity contributed to electrical instability as compared to non-failing rejected donor hearts. We conclude that microdomain coupling between Cx43 hemichannels and Ca2+ release is a novel, targetable, mechanism of cardiac arrhythmogenesis in heart failure.