Potassium channels in the Cx43 gap junction perinexus modulate ephaptic coupling: an experimental and modeling study
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It was recently demonstrated that cardiac sodium channels (Nav1.5) localized at the perinexus, an intercalated disc (ID) nanodomain associated with gap junctions (GJ), may contribute to electrical coupling between cardiac myocytes via an ephaptic mechanism. Impairment of ephaptic coupling by acute interstitial edema (AIE)-induced swelling of the perinexus was associated with arrhythmogenic, anisotropic conduction slowing. Given that Kir2.1 has also recently been reported to localize at intercalated discs, we hypothesized that Kir2.1 channels may reside within the perinexus and that inhibiting them may mitigate arrhythmogenic conduction slowing observed during AIE. Using gated stimulated emission depletion (gSTED) and stochastic optical reconstruction microscopy (STORM) super-resolution microscopy, we indeed find that a significant proportion of Kir2.1 channels resides within the perinexus. Moreover, whereas Nav1.5 inhibition during AIE exacerbated arrhythmogenic conduction slowing, inhibiting Kir2.1 channels during AIE preferentially increased transverse conduction velocity—decreasing anisotropy and ameliorating arrhythmia risk compared to AIE alone. Comparison of our results with a nanodomain computer model identified enrichment of both Nav1.5 and Kir2.1 at intercalated discs as key factors underlying the experimental observations. We demonstrate that Kir2.1 channels are localized within the perinexus alongside Nav1.5 channels. Further, targeting Kir2.1 modulates intercellular coupling between cardiac myocytes, anisotropy of conduction, and arrhythmia propensity in a manner consistent with a role for ephaptic coupling in cardiac conduction. For over half a century, electrical excitation in the heart has been thought to occur exclusively via gap junction-mediated ionic current flow between cells. Further, excitation was thought to depend almost exclusively on sodium channels with potassium channels being involved mainly in returning the cell to rest. Here, we demonstrate that sodium and potassium channels co-reside within nanoscale domains at cell-to-cell contact sites. Experimental and computer modeling results suggest a role for these channels in electrical coupling between cardiac muscle cells via an ephaptic mechanism working in tandem with gap junctions. This new insight into the mechanism of cardiac electrical excitation could pave the way for novel therapies against cardiac rhythm disturbances.
KeywordsCardiac conduction Gap junctions Sodium channels Potassium channels Arrhythmia Ephaptic coupling
The authors would like to thank Dr. James Smyth for the assistance with the STORM microscopy. Thanks also to Dr. Gregory Hoeker and Michael Entz for the assistance with optical mapping experiments and to Mrs. Jane Jourdan for the assistance with NRVM experiments.
Compliance with ethical standards
The investigation was conducted in conformation with the Guide for the Care and Use of Laboratory Animals published by the US National Institutes of Health (NIH publication no. 85-23, revised 1996). All animal study protocols were approved by the Institutional Animal Care and Use Committee (IACUC) at the Virginia Polytechnic University.
Conflicts of interest
The authors declare that they have no conflict of interest.
This work was supported by an NIH R01 grant awarded to Dr. Poelzing (R01-HL102298-01A1), by an NIH R01 grant awarded to Dr. Gourdie (RO1 HL56728-14A2), and by an American Heart Association post-doctoral fellowship awarded to Dr. Veeraraghavan (2013–15, completed).
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