A Mutation Causing Brugada Syndrome Identifies a Mechanism for Altered Autonomic and Oxidant Regulation of Cardiac Sodium Currents

Abstract

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.

“Heart Oddity”: Intrinsically Reduced Excitability in the Right Ventricle Requires Compensation by Regionally Specific Stress Kinase Function

“…(F,G) Physiological fluctuations of Nav 1.5 phosphorylation may lead to variations in excitability and conduction velocity [slower conduction with less phosphorylation (Zaitsev et al, 2019)]. While such variations are benign under normal conditions (F), they may lead to acute conduction crisis and reentrant arrhythmias when I Na expression is globally reduced (G) (Remme and Wilde, 2014), or when the phosphorylation balance of Nav 1.5 is compromised (Aiba et al, 2014) in patients with Brugada syndrome (BrS).…”

“…Interestingly, the conductivity of channels involved in the generation and transmission of the ventricular impulse (notably the cardiac Na + channel, Nav1.5) may be modulated by phosphorylation, and thus are amenable to regulation by protein kinases responding to various neural and hormonal signals, in particular transmitted through activation of G-protein-coupled receptors (GPCRs) (Sato et al, 2015). Prominent in these signaling pathways are the calcium/calmodulin-dependent protein kinase II (CaMKII) (Hund et al, 2010;Ashpole et al, 2012;Glynn et al, 2015;Burel et al, 2017) and the cAMP-activated protein kinase A (PKA) (Murphy et al, 1996;Zhou et al, 2002;Aiba et al, 2014), collectively known as "stress" kinases for their involvement in the "fight or flight" physiological response (Wehrens et al, 2004;Wu et al, 2016). This mini-review will focus on very recent (and still limited) information regarding how the electrical wave propagation through ventricular chambers is regulated by stress kinases.…”

High-throughput reclassification ofSCN5Avariants

“…because of other proteins that interact with or modify NaV1.5. [57][58][59] This study only examined a single splice isoform and the most common haplotype (H558) of SCN5A; for some variants, it has been shown that alternate haplotypes/isoforms can affect channel properties. 60 Conclusion: This study used automated patch clamping to study 73 previously unstudied SCN5A variants, resulting in the reclassification of 50/60 variants of uncertain significance.…”

Cardiac Na Channels

“…Changes in the NAD(H) balance has been shown to promote mitochondrial ROS production, which leads to a reduction in Na V 1.5 peak current, which may provide a link between altered metabolism, excitability, conduction block, and arrhythmic risk (Liu et al, 2013, 2010). Indeed, naturally occurring disease-linked mutations that have been shown to prevent the protein kinase A potentiation of Na V 1.5 during oxidative stress, leading to loss of Na channel function and manifestations of Brugada syndrome (Aiba et al, 2014). …”