Cx43 hemichannel microdomain signaling at the intercalated disc enhances cardiac excitability
Maarten A.J. De Smet, … , Karin R. Sipido, Luc Leybaert
Maarten A.J. De Smet, … , Karin R. Sipido, Luc Leybaert
Published February 23, 2021
Citation Information: J Clin Invest. 2021;131(7):e137752. https://doi.org/10.1172/JCI137752.
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Research Article Cardiology Cell biology

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 about the 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 were activated during diastolic Ca2+ release in single ventricular cardiomyocytes and cardiomyocyte cell pairs from mice and pigs. 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 compared with nonfailing rejected donor hearts. We conclude that microdomain coupling between Cx43 hemichannels and Ca2+ release is a potentially novel, targetable mechanism of cardiac arrhythmogenesis in heart failure.

Authors

Maarten A.J. De Smet, Alessio Lissoni, Timur Nezlobinsky, Nan Wang, Eef Dries, Marta Pérez-Hernández, Xianming Lin, Matthew Amoni, Tim Vervliet, Katja Witschas, Eli Rothenberg, Geert Bultynck, Rainer Schulz, Alexander V. Panfilov, Mario Delmar, Karin R. Sipido, Luc Leybaert

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Figure 10

Identification and regulation of Cx43 hemichannels in nonfailing and failing human ventricular cardiomyocytes.

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Identification and regulation of Cx43 hemichannels in nonfailing and fai...
(A) Unitary current example traces during first and second caffeine applications, NCX current subtracted. Recorded in nonfailing left ventricular human cardiomyocyte. (B) Summary dot plot and transition histogram indicating significantly reduced unitary current event probability during the second caffeine pulse (red) compared with the first (black) (nested t test; N/nNF = 20/64). (C) IV plots depicting linear current-voltage relationship with slope conductance approximately 220 pS and Erev ≈ 0 mV (NNF/nNF = 4/14). (D) Ca2+ release–induced unitary current example traces following 0.5 and 2 Hz pacing in nonfailing and failing human cardiac myocytes (NCX currents subtracted). (E) Summary graph and transition histograms indicate significant increase in unitary current event probability with increasing pacing frequency (nested t test; N/nNF = 5/25, N/nHF = 5/25). This effect is significantly stronger at 2 Hz in failing compared with nonfailing cardiomyocytes (nested t test). (F) Ca2+ release–induced unitary current example traces in the absence and presence of isoproterenol (10 nmol/L) in nonfailing and failing human cardiac myocytes (NCX currents subtracted). (G) Summary graph and transition histograms indicate significant increase in unitary current event probability with isoproterenol compared with baseline (nested t test; N/nNF = 5/13, N/nHF = 5/14). The effect was significantly stronger with ISO in failing compared with nonfailing cardiomyocytes (nested t test). (H) Ca2+ release–induced unitary current example traces during fast pacing and adrenergic stimulation in nonfailing and failing human cardiomyocytes. Including Gap19 in the pipette solution abolished unitary current activity (NCX currents subtracted). (I) Summary dot plot and transition histogram illustrating increased event probability in failing compared with nonfailing myocytes. Gap19 significantly reduced event probability in nonfailing and failing cardiomyocytes (nested 1-way ANOVA; N/nNF = 4/15, N/nHF = 5/15).