Caveolin-3 suppresses late sodium current by inhibiting nNOS-dependent S-nitrosylation of SCN5A

Aims: Mutations in CAV3-encoding caveolin-3 (Cav3) have been implicated in type 9 long QT syndrome (LQT9) and sudden infant death syndrome (SIDS). When co-expressed with SCN5A-encoded cardiac sodium channels these mutations increased late sodium current (I_Na) but the mechanism was unclear. The present study was designed to address the mechanism by which the LQT9-causing mutant Cav3-F97C affects the function of caveolar SCN5A. Methods and results: HEK-293 cells expressing SCN5A and LQT9 mutation Cav3-F97C resulted in a 2-fold increase in late I_Na compared to Cav3-WT. This increase was reversed by the neural nitric oxide synthase (nNOS) inhibitor L-NMMA. Based on these findings, we hypothesized that an nNOS complex mediated the effect of Cav3 on SCN5A. A SCN5A macromolecular complex was established in HEK-293 cells by transiently expressing SCN5A, α1-syntrophin (SNTA1), nNOS, and Cav3. Compared with Cav3-WT, Cav3-F97C produced significantly larger peak I_Na amplitudes, and showed 3.3-fold increase in the late I_Na associated with increased S-nitrosylation of SCN5A. L-NMMA reversed both the Cav3-F97C induced increase in late and peak I_Na and decreased S-nitrosylation of SCN5A. Overexpression of Cav3-F97C in adult rat cardiomyocytes caused a significant increase in late I_Na compared to Cav3-WT, and prolonged the action potential duration (APD90) in a nNOS-dependent manner. Conclusions: Cav3 is identified as an important negative regulator for cardiac late I_Na via nNOS dependent direct S-nitrosylation of SCN5A. This provides a molecular mechanism for how Cav3 mutations increase late I_Na to cause LQT9. This article is part of a Special Issue entitled "Na⁺ Regulation in Cardiac Myocytes".