Novel LQT-3 mutation affects Na+ channel activity through interactions between alpha- and beta1-subunits

Area of Science:

• Cardiology
• Molecular Biology
• Genetics

Background:

• Congenital long-QT syndrome (LQT) is an inherited cardiac arrhythmia causing prolonged ventricular repolarization.
• Mutations in SCN5A, encoding the human cardiac sodium channel alpha-subunit, are a known cause of LQT3.
• Previous LQT3 mutations in SCN5A result in sodium channels that reopen, directly causing delayed repolarization.

Purpose of the Study:

• To investigate the functional consequences of a novel SCN5A mutation (D1790G) found in an LQT family.
• To determine the impact of this mutation on sodium channel activity, both alone and in combination with the beta1-subunit.

Main Methods:

• Whole-cell patch-clamp electrophysiology was used to analyze wild-type and D1790G mutant SCN5A channels expressed in HEK 293 cells.
• Experiments involved transient transfection with SCN5A alpha-subunit cDNA, alone or coexpressed with human Na+ channel beta1-subunit (hbeta1) cDNA.
• Biophysical properties, including steady-state inactivation and sustained inward currents, were measured.

Main Results:

• The D1790G mutation significantly shifted steady-state inactivation of heteromeric alpha- and beta1-subunit channels by -16 mV.
• No D1790G-induced sustained inward current was observed.
• The mutation did not significantly affect the biophysical properties of monomeric alpha-subunits (hH1).

Conclusions:

• The novel D1790G mutation in SCN5A alters the inactivation properties of heteromeric cardiac sodium channels.
• These alterations are likely due to disrupted interactions between the SCN5A alpha- and beta1-subunits.
• The findings provide new insights into the molecular mechanisms underlying LQT3 caused by SCN5A mutations.