Computer simulation of wild-type and mutant human cardiac Na+ current

Area of Science:

• Molecular Cardiology
• Computational Biology
• Electrophysiology

Background:

• Inherited cardiac arrhythmias like Long QT syndrome (LQTS) and Brugada syndrome (BrS) predispose individuals to sudden cardiac death.
• Mutations in cardiac ion channel genes, particularly SCN5A encoding the sodium channel, are implicated in LQTS and BrS.
• Novel SCN5A mutations Y1795C and Y1795H identified at the same codon exhibit distinct disease phenotypes.

Purpose of the Study:

• To computationally simulate and analyze the functional consequences of SCN5A mutations Y1795C (LQTS) and Y1795H (BrS).
• To investigate the impact of these mutations on cardiac sodium current (I(Na)) and ventricular myocyte action potential morphology 'in silico'.

Main Methods:

• Development and application of a nine-state Markov model for cardiac sodium channels.
• Simulation of wild-type and mutant (Y1795C, Y1795H) I(Na) based on voltage-clamp experimental data.
• Integration of the Markov model into the Luo-Rudy ventricular myocyte model to assess action potential changes.

Main Results:

• Both Y1795C and Y1795H mutations altered sodium channel inactivation, leading to sustained I(Na).
• The Markov model accurately reproduced experimentally observed I(Na) alterations in mutant channels.
• In silico simulations showed Y1795C mutation prolonged action potential duration, consistent with LQTS, while Y1795H caused minimal changes, aligning with BrS.

Conclusions:

• The study successfully models the electrophysiological effects of distinct SCN5A mutations.
• Computational modeling provides valuable insights into genotype-phenotype correlations in inherited arrhythmia syndromes.
• The findings underscore the critical role of sodium channel function in cardiac electrical stability and disease pathogenesis.