Abstract 17175: Caveolin-3 Suppresses Late Sodium Current by Inhibiting Nnos-Dependent S-Nitrosylation of Scn5a
Background: Mutations in CAV3 —encoding Caveolin-3 (Cav3) have been implicated in arrhythmia syndromes such as long QT Syndrome type 9 (LQT9) and sudden infant death syndrome (SIDS). When coexpressed with SCN5A —encoded Nav1.5, these mutations result in a gain-of-function molecular phenotype by increasing late sodium current (I Na). Objetive To determine the mechanism by which LQT9-causing mutant Cav3-F97C affects the function of Nav1.5.
Methods and Results: HEK-293 cells expressing SCN5A and Cav3-F97C resulted in a 2-fold increase in late I Na compared to Cav3-WT and this effect was reversed by the neural nitric oxide synthase (nNOS) inhibitor L-NMMA. Based on these findings we hypothesized that the nNOS complex was involved in the modulatory effect of Cav3 on Nav1.5 channels. A Nav1.5 macromolecular complex was established in HEK-293 cells by transiently expressing SCN5A, α1-syntrophin (SNTA1), nNOS, and Cav3. Compared with Cav3-WT, Cav3-F97C had significantly larger peak I Na amplitudes, and showed a 3.3-fold increase in the late I Na and an increase in S-nitrosylation of SCN5A. When treated with L-NMMA, the Cav3-F97C-induced increase in both late and peak I Na was reversed, and S-nitrosylation of SCN5A for Cav3-F97C was minimal. In adult rat cardiomyocytes overexpressing Cav3, Cav3-F97C caused a significant increase in late I Na compared to Cav3-WT, and prolonged action potential duration (APD90) in a nNOS-dependent manner.
Conclusions: These results identify Cav3 as an important negative regulator for cardiac late I Na via nNOS-dependent direct S-nitrosylation of SCN5A, and indicates the molecular mechanism for LQT9 to be the loss of this inhibition by Cav3-F97C resulting in increased late I Na.
- © 2010 by American Heart Association, Inc.