Gating pore currents are defects in common with two Nav1.5 mutations in patients with mixed arrhythmias and dilated cardiomyopathy.
Bottom Line: The gating pore current, also called omega current, consists of a cation leak through the typically nonconductive voltage-sensor domain (VSD) of voltage-gated ion channels.Two Na(v)1.5 mutations (R222Q and R225W) located in the VSD are associated with atypical clinical phenotypes involving complex arrhythmias and dilated cardiomyopathy.Using the patch-clamp technique, in silico mutagenesis, and molecular dynamic simulations, we tested the hypothesis that these two mutations may generate gating pore currents, potentially accounting for their clinical phenotypes.
Affiliation: Centre de Recherche de L'Institut Universitaire en Santé Mentale de Québec, Québec City, Québec G1J 2G3, Canada.Show MeSH
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Mentions: It was recently proposed that arginine mutations inside the VSD would cause a loss of mobility (or a partial freezing) of the S4 after long depolarization periods (Sokolov et al., 2008; Fan et al., 2013; Groome et al., 2014). In the presence of 10 µM TTX, a 500-ms predepolarization was used to mimic the cardiac AP duration. We then applied a ramp protocol from −140 to 0 mV at 0.72 mV/ms to measure gating pore current (see protocol in inset of Fig. 6). At hyperpolarized potentials, gating pore currents were observed after a long depolarization for both R222Q and R225W mutations (−5.6 ± 1.1 pA/pF, n = 5, for R222Q and −3.3 ± 0.6, n = 3, for R225W) and were absent for the WT (−0.9 ± 0.1 pA/pF, n = 5). Such currents could not be observed without the 500-ms predepolarization (Fig. 6). These results show that after long depolarization periods, the mutated S4 segments need more time to resume their resting position and thus partially remain in a conformation, likely enabling gating pore current conduction.
Affiliation: Centre de Recherche de L'Institut Universitaire en Santé Mentale de Québec, Québec City, Québec G1J 2G3, Canada.