Correlations between clinical and physiological consequences of the novel mutation R878C in a highly conserved pore residue in the cardiac Na⁺ channel

• Published in: Acta Physiologica 2008-12, Vol.194 (4), p.311-323
• Main Authors: Zhang, Y, Wang, T, Ma, A, Zhou, X, Gui, J, Wan, H, Shi, R, Huang, C, Grace, A.A, Huang, C.L.-H, Trump, D, Zhang, H, Zimmer, T, Lei, M
• Format: Article
• Language: English
• Subjects: Adult; Animals; Arrhythmias, Cardiac - genetics; Arrhythmias, Cardiac - metabolism; Biological and medical sciences; cardiac Na+ channels; cardiac Na⁺ channels; Cardiovascular; Electrocardiography; Female; Fundamental and applied biological sciences. Psychology; Heterozygote; Humans; Immunohistochemistry; Male; Microscopy, Confocal; Mutation - genetics; Myocardium - metabolism; novel mutation; Pedigree; pore-forming region; SCN5A; sick sinus syndrome; Sick Sinus Syndrome - genetics; Sick Sinus Syndrome - metabolism; Sodium Channels - genetics; Vertebrates: anatomy and physiology, studies on body, several organs or systems; Xenopus
• ISSN: 1748-1708; 1748-1716
• DOI: 10.1111/j.1748-1716.2008.01883.x

We compared the clinical and physiological consequences of the novel mutation R878C in a highly conserved pore residue in domain II (S5-S6) of human, hNav1.5, cardiac Na⁺ channels. Full clinical evaluation of pedigree members through three generations of a Chinese family combined with SCN5A sequencing from genomic DNA was compared with patch and voltage-clamp results from two independent expression systems. The four mutation carriers showed bradycardia, and slowed sino-atrial, atrioventricular and intraventricular conduction. Two also showed sick sinus syndrome; two had ST elevation in leads V1 and V2. Unlike WT-hNav1.5, whole-cell patch-clamped HEK293 cells expressing R878C-hNav1.5 showed no detectable Na⁺ currents (iNa), even with substitution of a similarly charged lysine residue. Voltage-clamped Xenopus oocytes injected with either 0.04 or 1.5 μg μL⁻¹ R878C-hNav1.5 cRNA similarly showed no iNa, yet WT-hNav1.5 cRNA diluted to 0.0004-0.0008 ng μL⁻¹resulted in expression of detectable iNa. iNa was simply determined by the amount of injected WT-hNav1.5: doubling the dose of WT-hNav1.5 cRNA doubled iNa. iNa amplitudes and activation and inactivation characteristics were similar irrespective of whether WT-hNav1.5 cRNA was given alone or combined with equal doses of R878C-hNav1.5 cRNA therefore excluding dominant negative phenotypic effects. Na⁺ channel function in HEK293 cells transfected with R878C-hNav1.5 was not restored by exposure to mexiletine (200 μ m) and lidocaine (100 μ m). Fluorescence confocal microscopy using E3-Nav1.5 antibody demonstrated persistent membrane expression of both WT and R878C-hNav1.5. Modelling studies confirmed that such iNa reductions reproduced the SSS phenotype. Clinical consequences of the novel R878C mutation correlate with results of physiological studies.