The SCN5A double mutant R1232W/T1620M abolished functional sodium channel expression and was retained within the endoplasmic reticulum compared to cell surface localization of wild-type channels.
Does the SCN5A double mutant R1232W/T1620M alter functional expression and cellular localization of cardiac sodium channels compared to wild-type?
The SCN5A double mutant R1232W/T1620M causes loss of function of the cardiac Na+ channel by trapping the protein in the endoplasmic reticulum, supporting its role in Brugada syndrome.
Brugada syndrome is an inherited cardiac disorder caused by mutations in the cardiac sodium channel gene, SCN5A, that leads to ventricular fibrillation and sudden death. This study reports the changes in functional expression and cellular localization of an SCN5A double mutant (R1232W/T1620M) recently discovered in patients with Brugada syndrome. Mutant and wild-type (WT) human heart sodium channels (hNa(v)1.5) were expressed in tsA201 cells in the presence of the beta(1)-auxiliary subunit. Patch-clamp experiments in whole-cell configuration were conducted to assess functional expression. Immunohistochemistry and confocal microscopy were used to determine the spatial distribution of either WT or mutant cardiac sodium channels. The results show an abolition of functional sodium channel expression of the hNa(v)1.5/R1232W/T1620M mutant in the tsA201 cells. A conservative positively charged mutant, hNa(v)1.5/R1232K/T1620M, produced functional channels. Immunofluorescent staining showed that the FLAG-tagged hNa(v)1.5/WT transfected into tsA201 cells was localized on the cell surface, whereas the FLAG-tagged hNa(v)1.5/R1232W/T1620M mutant was colocalized with calnexin within the endoplasmic reticulum (ER). These results indicate that a positively charged arginine or lysine residue at position 1232 in the double mutant is required for the proper transport and functional expression of the hNa(v)1.5 protein. These results support the concept that loss of function of the cardiac Na(+) channel is responsible for the Brugada syndrome. The full text of this article is available at http://www.circresaha.org.
Baroudi et al. (Fri,) conducted a other in Brugada syndrome. SCN5A double mutant R1232W/T1620M vs. Wild-type (WT) human heart sodium channels was evaluated on Functional sodium channel expression and spatial distribution. The SCN5A double mutant R1232W/T1620M abolished functional sodium channel expression and was retained within the endoplasmic reticulum compared to cell surface localization of wild-type channels.