Novel mechanism forBrugada syndrome - Defective surface localization of anSCN5A 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 SC N5A underlie Brugada syndrome, an inherited disorder that leads to ventricu lar fibrillation and sudden death. This study describes changes in cellular localization and functional expression of hH1 in a naturally occurring SCN SA mutation (R1432G) reported for Brugada syndrome. Using patch-clamp exper iments, we show that there is an abolition of functional hi-Il expression i n R1432G mutants expressed in human tsA201 cells but not in Xenopus oocytes . In tsA201 cells, a conservative positively charged mutant, R1432K, produc ed sodium currents with normal gating properties, whereas other mutations a t this site abolished functional sodium channel expression. Immunofluoresce nt staining and confocal microscopy showed that the wild-type alpha subunit expressed in tsA201 cells was localized to the cell surface, whereas the R 1432G mutant was colocalized with calnexin within the endoplasmic reticulum . The beta (1) subunit was also localized to the cell surface in the presen ce of the a subunit; however, in its absence, the beta (1) subunit was rest ricted to a perinuclear localization. These results demonstrate that the di sruption of SCN5A cell-surface localization is one mechanism that can accou nt for the loss of functional sodium channels in Brugada syndrome. The full text of this article is available at http://www.circresaha.org.