Involvement of IsK-associated K⁺ channel in heart rate control of repolarization in a murine engineered model of Jervell and Lange-Nielsen syndrome

The Jervell and Lange-Nielsen (JLN) syndrome affects the human cardioauditory system, associating a profound bilateral deafness with an abnormally long QT interval on the ECG. It results from mutations in KVLQT1 and ISK genes that encode the 2 subunits forming the K⁺ channel responsible for the cardiac and inner ear slowly activating component of the delayed rectifier K⁺ current (I(Ks)). A JLN mouse model that presents typical inner ear defects has been created by knocking out the isk gene (isk-/-). This study specifically reports on the cardiac phenotype counterpart, determined in the whole animal and at mRNAs and cellular levels. Surface ECG recordings of isk-/- mice showed a longer QT interval at slow heart rates, a paradoxical shorter QT interval at fast heart rates, and an overall exacerbated QT-heart rate adaptation compared with wild-type (WT) mice. A 300-ms increase in the heart rate cycle length induces a 309 ± 21% increase in the QT duration of the WT mice versus a 500 ± 50% in isk-/- mice (p<0.001). It is concluded that the isk gene product and/or I(Ks), when present, blunts the QT adaptation to heart rate variations and that steeper QT-RR relationships reflect a greater susceptibility to arrhythmias in patients lacking I(Ks).