BACKGROUND: The slow delayed rectifier potassium current IKs is crucial for the repolarization of the cardiac action potential. It is conducted by the voltage-gated channel Kv 7.1 encoded by KCNQ1, together with its β-subunit KCNE1. Loss-of-function mutations in KCNQ1 have been associated with heritable cardiac arrhythmias such as LQT syndrome. This disease is characterized by prolonged ventricular repolarization and propensity to ventricular tachyarrhythmia that may lead to syncope, cardiac arrest, and sudden death. We aimed to functionally characterize two Kv 7.1 mutations (p.A150T and p.L374H) identified in two independent LQTS patients with different severity of disease phenotype, family history and co-segregation of LQTS.

METHODS: We performed whole-cell patch clamp recordings in CHO-K1 cells, and confocal imaging in Madin Darby Canine Kidney (MDCK) cells.

RESULTS: IKs -A150T showed significantly decreased current amplitude from above +20 mV (approx. 52% decrease at +40 mV), but demonstrated cell membrane localization similar to wild-type (WT). IKs -L374H, however, exhibited a complete loss-of-function compared to WT channels. Confocal imaging showed ER retention of the channel in MDCK cells. Mimicking the heterozygous state of the patients by co-expressing WT and mutant subunits resulted in an approx. 22% decrease in current at +40 mV for A150T. The L374H mutation showed a more pronounced effect (62% reduction at +40 mV compared to WT channel).

CONCLUSION: Both mutations, Kv 7.1 A150T and L374H, led to loss of channel function. The degree of loss-of-function may mirror the disease phenotype observed in the patients. This article is protected by copyright. All rights reserved.