Novel mechanism for Brugada syndrome: defective surface localization of an SCN5A mutant (R1432G).

The SCN5A gene encodes the alpha subunit of the human heart sodium channel (hH1), which plays a critical role in cardiac excitability. Mutations of SCN5A underlie Brugada syndrome, an inherited disorder that leads to ventricular fibrillation and sudden death. This study describes changes in cellular localization and functional expression of hH1 in a naturally occurring SCN5A mutation (R1432G) reported for Brugada syndrome. Using patch-clamp experiments, we show that there is an abolition of functional hH1 expression in R1432G mutants expressed in human tsA201 cells but not in Xenopus oocytes. In tsA201 cells, a conservative positively charged mutant, R1432K, produced sodium currents with normal gating properties, whereas other mutations at this site abolished functional sodium channel expression. Immunofluorescent staining and confocal microscopy showed that the wild-type alpha subunit expressed in tsA201 cells was localized to the cell surface, whereas the R1432G mutant was colocalized with calnexin within the endoplasmic reticulum. The beta(1) subunit was also localized to the cell surface in the presence of the alpha subunit; however, in its absence, the beta(1) subunit was restricted to a perinuclear localization. These results demonstrate that the disruption of SCN5A cell-surface localization is one mechanism that can account for the loss of functional sodium channels in Brugada syndrome. The full text of this article is available at http://www.circresaha.org.