Abstract 376: Acute Modulation of Sodium Channel Auxiliary Subunit β1-mediated Adhesion: a Novel Antiarrhythmic Strategy

Abstract

Cardiac impulse propagation is thought to occur by direct cell to cell flow of current via connexin43 (Cx43) gap junctions (GJs). We recently demonstrated that cardiac sodium channels (Na v 1.5) localized within the perinexus, an intercalated disk (ID) nanodomain adjacent to Cx43 GJ, may enable ephaptic coupling between cardiac myocytes. We hypothesized that β1-mediated adhesion may closely approximate membranes within ID nanodomains, facilitating ephaptic coupling. Super-resolution STochastic Optical Reconstruction Microscopy-based Relative Localization Analysis (STORM-RLA) and immuno-electron microscopy identified two Na V 1.5 populations within the ID in guinea pig ventricles (GPVs): A perinexal population, accounting for 47% of ID-localized Na V 1.5 and a plicate population, co-distributing with N-Cadherin, accounting for 29%. β1 was preferentially localized to the perinexus (48% of ID-localized β1) over N-Cadherin-rich plicate regions (8%). βadp1, a novel peptide inhibitor of β1 adhesion, selectively and dose-dependently inhibited barrier function in β1-overexpressing 1610 cells in electric cell-substrate impedance spectroscopy studies. Neither βadp1 nor a scrambled control peptide (βadp1-scr) affected I Na or action potentials in isolated GPV myocytes. However, βadp1 reduced peak current recorded from Na V 1.5 clusters adjacent Cx43-EGFP at cell-cell contacts using scanning ion conductance microscopy-guided patch clamp. In GPVs, βadp1 (100 μM) compromised the diffusion-resistance of the ID as assessed by perfusion of fixable fluorescent dyes. βadp1 (48±4 μm) but not βadp1-scr (22±1 μm) increased perinexal intermembrane spacing compared to control GPVs (17±1μm). Optical mapping revealed that βadp1 but not βadp1-scr slowed conduction in GPVs and iPSC-derived cardiomyocyte monolayers. Importantly, in GPVs, βadp1 increased conduction anisotropy and precipitated spontaneous tachyarrhythmias in a dose-dependent manner. Thus, β1-mediated adhesion generates close apposition between Na V 1.5-rich perinexal membranes, facilitating ephaptic conduction in the heart. Importantly, β1-mediated adhesion may be a target for novel, mechanistically-driven antiarrhythmic therapy.