Abstract 13129: Acute Inhibition of Sodium Channel Beta Subunit (β1) -mediated Adhesion is Highly Proarrhythmic
Introduction: The sodium channel auxiliary subunit and cell adhesion molecule β1 (SCN1b) is enriched at cardiomyocyte intercalated disks (ID) along with the pore-forming subunit NaV1.5. We recently demonstrated that the perinexus, an NaV1.5-rich ID nanodomain located near connexin43 (Cx43) gap junctions (GJ), is important for cell-to-cell electrical coupling. Disrupting close membrane apposition within the perinexus was highly proarrhythmic.
Hypothesis: β1-mediated adhesion is key to close membrane apposition within the perinexus; therefore, inhibiting β1-mediated adhesion may disrupt perinexal structure, impair conduction and precipitate arrhythmias.
Methods and Results: NaV1.5 and β1 localization within ID nanodomains was quantitatively assessed from super-resolution STochastic Optical Reconstruction Microscopy (STORM) images of en face IDs from adult guinea pig ventricles. NaV1.5 and β1 were located 63±15 and 75±25 nm from Cx43 GJ; 31% of both NaV1.5 and β1 localized to GJ perinexi. β1-mediated adhesion was acutely inhibited by βadp1, a novel peptide mimetic of β1’s putative extracellular adhesion domain. βadp1 decreased cellular adhesion as assessed by Electric Cell-Substrate Impedance Spectroscopy (ECIS) in β1-overexpressing 1610 cells in a dose-dependent manner but not in native 1610 cells. Perinexal intermembrane spacing as measured by Transmission Electron Microscopy (TEM) increased 3-fold from 17±1 nm in vehicle controls (0.25% DMSO) to 49±5 nm (p<0.05) in 100 μM βadp1-treated hearts; however, intermembrane spacing at other ID locations was unaltered (22±1 vs. 24±1 nm). Optical mapping revealed preferential slowing of transverse conduction (8.0±0.7 vs. 16.5±1.2 cm/s, p<0.05) and increased anisotropy (3.9±0.2 vs. 2.6±0.2, p<0.05) in βadp1-treated hearts relative to vehicle controls. Further, 3 of 4 βadp1-treated hearts exhibited spontaneous ventricular tachycardias.
Conclusions: These data support a role for β1-mediated adhesion in maintaining close apposition between NaV1.5-rich perinexal membranes. Importantly, acute inhibition of β1-mediated adhesion resulted in disruption of close membrane apposition within the GJ perinexus and precipitated severe conduction slowing and spontaneous arrhythmias.
Author Disclosures: R. Veeraraghavan: None. G.S. Hoeker: None. S. Poelzing: None. R.G. Gourdie: None.
- © 2016 by American Heart Association, Inc.