Single-Molecule Localization of the Cardiac Voltage-Gated Sodium Channel Reveals Different Modes of Reorganization at Cardiomyocyte Membrane Domains

Background: Mutations in the gene encoding the cardiac voltage-gated sodium channel Na v 1.5 cause various cardiac arrhythmias. This variety may arise from different determinants of Na v 1.5 expression between cardiomyocyte domains. At the lateral membrane and T-tubules, Na v 1.5 localization and function remain insufficiently characterized. Methods: We used novel single-molecule localization microscopy and computational modeling to define nanoscale features of Na v 1.5 localization and distribution at the lateral membrane, the lateral membrane groove, and T-tubules in cardiomyocytes from wild-type (N=3), dystrophin-deficient ( mdx ; N=3) mice, and mice expressing C-terminally truncated Na v 1.5 (ΔSIV; N=3). We moreover assessed T-tubules sodium current by recording whole-cell sodium currents in control (N=5) and detubulated (N=5) wild-type cardiomyocytes. Results: We show that Na v 1.5 organizes as distinct clusters in the groove and T-tubules which density, distribution, and organization partially depend on SIV and dystrophin. We found that overall reduction in Na v 1.5 expression in mdx and ΔSIV cells results in a nonuniform redistribution with Na v 1.5 being specifically reduced at the groove of ΔSIV and increased in T-tubules of mdx cardiomyocytes. A T-tubules sodium current could, however, not be demonstrated. Conclusions: Na v 1.5 mutations may site-specifically affect Na v 1.5 localization and distribution at the lateral membrane and T-tubules, depending on site-specific interacting proteins. Future research efforts should elucidate the functional consequences of this redistribution.