Abstract
Voltage gated sodium channels (Nav) are transmembrane proteins responsible for action potential initiation. Mutations mainly located in the voltage sensor domain (VSD) of Nav1.5, the cardiac sodium channel, have been associated with the development of arrhythmias combined with dilated cardiomyopathy. Gating pore currents have been observed with three unrelated mutations associated with similar clinical phenotypes. However, gating pores have never been associated with mutations outside the first domain of Nav1.5. The aim of this study was to explore the possibility that gating pore currents might be caused by the Nav1.5 R225P and R814W mutations (R3, S4 in DI and DII, respectively), which are associated with rhythm disturbances and dilated cardiomyopathy. Nav1.5 WT and mutant channels were transiently expressed in tsA201 cells. The biophysical properties of the alpha pore currents and the presence of gating pore currents were investigated using the patch-clamp technique. We confirmed the previously reported gain of function of the alpha pores of the mutant channels, which mainly consisted of increased window currents mostly caused by shifts in the voltage dependence of activation. We also observed gating pore currents associated with the R225P and R814W mutations. This novel permeation pathway was open under depolarized conditions and remained temporarily open at hyperpolarized potentials after depolarization periods. Gating pore currents could represent a molecular basis for the development of uncommon electrical abnormalities and changes in cardiac morphology. We propose that this biophysical defect be routinely evaluated in the case of Nav1.5 mutations on the VSD.
Highlights
Voltage-gated sodium channels (Nav) are transmembrane proteins responsible for the initiation and propagation of action potentials in many excitable cells
The S1– S4 segments of each domain make up the voltage sensor domain (VSD), which modulates the activity of the channel through conformational changes induced by variations in the transmembrane voltage
We further propose that this pathway should be routinely evaluated in future studies on SCN5A mutations in the VSD of the channel that are associated with arrhythmias and dilated cardiomyopathy
Summary
Voltage-gated sodium channels (Nav) are transmembrane proteins responsible for the initiation and propagation of action potentials in many excitable cells. Cardiac action potentials are initiated by Nav1.5, the main Nav isoform in the heart. This large 2016-amino-acid protein is encoded by the SCN5A gene and is composed of 24 transmembrane segments organized in four homologous. The assembly of the S5–S6 segments of each domain forms the alpha pore, which is responsible for the selective permeation of Na+ ions that underlies the physiological functions of the channel. Nav1.5 dysfunctions result in cardiac pathologies such as Brugada syndrome, type 3 Long QT syndrome, sick sinus syndrome, and cardiac conduction disorders with no structural heart disease (Amin et al, 2010)
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