A Mutation Causing Brugada Syndrome Identifies a Mechanism for Altered Autonomic and Oxidant Regulation of Cardiac Sodium Currents
Background—The mechanisms of the electrocardiographic changes and arrhythmias in Brugada syndrome (BrS) remain controversial. Mutations in the sodium channel gene, SCN5A and regulatory proteins that reduce or eliminate sodium current (INa) have been linked to BrS. We studied the properties of a BS-associated SCN5A mutation in a protein kinase A (PKA) consensus phosphorylation site, R526H.
Methods and Results—In-vitro PKA phosphorylation was detected in the I-II linker peptide of wild type (WT) channels but not R526H or S528A (phosphorylation site) mutants. Cell surface expression of R526H and S528A channels were reduced compared with WT. Whole-cell INa through all channel variants revealed no significant differences in the steady-state activation, inactivation and recovery from inactivation. Peak current densities of the mutants were significantly reduced compared to WT. Infection of 2D cultures of neonatal rat ventricular myocytes with WT and mutant channels increased conduction velocity (CV) compared with non-infected cells. PKA stimulation significantly increased peak INa and CV of WT but not mutant channels. Oxidant stress inhibits cardiac Na currents; WT and mutant INa decreases with the intracellular application of NADH, an effect that is reversed by PKA stimulation in WT but not in R526H or S528A channels.
Conclusions—We identified a family with BrS and an SCN5A mutation in a PKA consensus phosphorylation site. The BrS mutation R526H is associated with a reduction in the basal level of INa and a failure of PKA stimulation to augment the current which may contribute to the predisposition to arrhythmias in patients with BrS, independent of the precipitants.
- protein kinase A phosphorylation
- ion channel
- reactive oxygen species
- SCN5A, mutation
- sudden cardiac death
- adrenergic stimulation
- Received August 26, 2013.
- Revision received March 13, 2014.
- Accepted March 23, 2014.