Mexiletine rescues a mixed biophysical phenotype of the cardiac sodium channel arising from the SCN5a mutation, N406K, found in LQT3 patients

Rou Mu Hu, David J. Tester, Ryan Li, Tianyu Sun, Blaise Z. Peterson, Michael John Ackerman, Jonathan C. Makielski, Bi Hua Tan

Research output: Contribution to journalArticle


Introduction: Individual mutations in the SCN5A-encoding cardiac sodium channel α-subunit usually cause a single cardiac arrhythmia disorder, some cause mixed biophysical or clinical phenotypes. Here we report an infant, female patient harboring a N406K mutation in SCN5A with a marked and mixed biophysical phenotype and assess pathogenic mechanisms. Methods and Results: A patient suffered from recurrent seizures during sleep and torsades de pointes with a QTc of 530 ms. Mutational analysis identified a N406K mutation in SCN5A. The mutation was engineered by site-directed mutagenesis and heterologously expressed in HEK293 cells. After 48 hours incubation with and without mexiletine, macroscopic voltage-gated sodium current (INa) was measured with standard whole-cell patch clamp techniques. SCN5A-N406K elicited both a significantly decreased peak INa and a significantly increased late INa compared to wide-type (WT) channels. Furthermore, mexiletine both restored the decreased peak INa of the mutant channel and inhibited the increased late INa of the mutant channel. Conclusion: SCN5A-N406K channel displays both “gain-of-function” in late INa and “loss-of-function” in peak INa density contributing to a mixed biophysical phenotype. Moreover, our finding may provide the first example that mexiletine exerts a dual rescue of both “gain-of-function” and “loss-of-function” of the mutant sodium channel.

Original languageEnglish (US)
Pages (from-to)176-186
Number of pages11
Issue number1
StatePublished - Jan 1 2018



  • Mexiletine
  • Mixed phenotype
  • Mutation
  • SCN5A
  • Sodium channel

ASJC Scopus subject areas

  • Biophysics
  • Biochemistry

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