Dominant-Negative Suppression of Sodium Channel Activity by a Brugada Syndrome Mutation Observed in Cardiomyocytes

Abstract

Brugada syndrome (BrS) is an inherited cardiac disease with an autosomal dominant pattern. Unfortunately, the molecular and cellular mechanisms leading to BrS are not yet completely understood. Recently, the L325R-SCN5A mutation has been proposed to cause BrS through a dominant negative effect. This usually occurs if the mutant channels interact with wild-type (WT) channels forming non-functional channel multimers. However, sodium channel α-subunits are not believed to oligomerize. Therefore, we tested whether the dominant-negative effect seen in some BrS mutations is due to interactions between sodium channel α-subunits. Here we found that when WT-SCN5A and L325R channels were co-transfected in a 1:1 ratio in HEK293 cells, the peak INa density was reduced to only 29.8±6.2% of control. Surprisingly, a similar dominant-negative effect was also observed when L325R-SCN5A was coexpressed with the WT skeletal muscle sodium channel (WT-SCN4A). Moreover, when L325R channels were expressed in neonatal rat ventricular myocytes (NRVM), the peak INa was also reduced by about 80% (peak current density at −10 mV=-32.5+14.9pA/pF), compared to non-transfected NRVMs (peak current density at −10 mV=-182.7+36.3pA/pF). As expected, overexpression of WT-SCN5A increased the peak INa (peak current density at −10 mV=-234.6+32.2pA/pF). Interestingly, L325R did not interfere with the proper function of IK1 in NRVM, suggesting a specific dominant negative effect of L325R channels on sodium channels. In conclusion, the dominant negative effect observed in some BrS mutations suggests an interaction of sodium channel α-subunits which appears to occur even across different sodium channel isoforms.Our findings demonstrate that the L325R allele exerts a dominant negative effect on WT channels not only in heterologous expression systems but also in native cardiomyocytes, which would explain the BrS phenotype seen in patients carrying this mutation.