C-terminal long-QT type 1 R562S-Kv7.1 variant, the first variant in helix C impairing β-adrenergic response of the slow delayed rectifier K⁺ channel

Kv7.1 variants, associated with long QT syndrome type 1 (LQT1) and altering the function of the slow delayed rectifier K⁺ (I_Ks) channel, may result in arrhythmias, especially during exercise. This study focused on complex analysis of the R562S-Kv7.1 variant located in helix C of the Kv7.1 C terminus, which was identified in four putatively unrelated families in the Czech Republic.

The clinical and genetic investigation was followed by functional analysis (whole-cell patch clamp, confocal microscopy, computational simulations) and structural modelling. The genetic analysis suggested that R562S-Kv7.1 might be a founder LQT1 variant in Central Europe. R562S carriers showed a significantly prolonged corrected QT (QTc) interval at rest and a significantly higher QTc prolongation after exercise vs. healthy relatives. The functional analysis of R562S channels demonstrated their preserved membrane localization, a significant decrease in I_Ks with a rightward shift of the voltage dependence of activation, and, importantly, a lack of responsiveness to β-adrenergic stimulation. The latter seems to be related to a modified interaction of the modulatory KCNE1 subunit with Kv7.1. The pro-arrhythmic potential of R562S dysfunction, mediated by delayed afterdepolarizations during β-adrenergic stimulation, could be effectively prevented by mild (5%) inhibition of L-type Ca²⁺ current (I_Ca).

R562S-Kv7.1 is the first variant in helix C causing an impaired response of I_Ks channel to β-adrenergic stimulation, likely due to altered interactions between channel subunits, namely Kv7.1 and KCNE1. Mild I_Ca inhibition was suggested as a new treatment option.