Zhang Y, Wang T, Ma A, Zhou X, Gui J, Wan H, Shi R, Huang C, Grace AA, Huang CL, Trump D, Zhang H, Zimmer T, Lei M
CORRELATIONS BETWEEN CLINICAL AND PHYSIOLOGICAL CONSEQUENCES OF THE NOVEL MUTATION R878C IN A HIGHLY CONSERVED PORE RESIDUE IN THE CARDIAC NA(+) CHANNEL. [JOURNAL ARTICLE]
Acta Physiol (Oxf) 2008 Jun 24.
Aim: We compared clinical and physiological consequences of novel mutation R878C in a highly conserved pore residue in domain II (S5-S6) of human, hNa(v)1.5, cardiac Na(+) channels.
Methods: 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.
Results: 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-hNa(v)1.5, whole-cell patch-clamped HEK293 cells expressing R878C-hNa(v)1.5 showed no detectable Na(+) currents (i(Na)), even with substitution of a similarly charged lysine residue. Voltage-clamped Xenopus oocytes injected with either 0.04 ng mul(-1) or 1.5 mug mul(-1) R878C-hNa(v)1.5 cRNA similarly showed no i(Na), yet WT-hNa(v)1.5 cRNA diluted to 0.0004-0.0008 ng mul(-1) provoked detectable i(Na). i(Na) was simply determined by the amount of injected WT-hNa(v)1.5: doubling the dose of WT-hNa(v)1.5 cRNA doubled i(Na). i(Na) amplitudes and activation and inactivation characteristics were similar whether WT-hNa(v)1.5 cRNA was given alone or combined with equal doses of R878C-hNa(v)1.5 cRNA therefore excluding dominant negative phenotypic effects. Na(+) channel function in HEK293 cells transfected with R878C-hNa(v)1.5 was not restored by exposure to mexiletine (200 muM) and lidocaine (100 muM). Fluorescence confocal microscopy using E3-Nav1.5 antibody demonstrated persistent membrane expression of both WT and R878C-hNa(v)1.5. Modeling studies confirmed such i(Na) reductions reproduced the SSS phenotype.
Conclusion: Clinical consequences of the novel R878C mutation correlate with results of physiological studies.
More from this journal |
