Novel Brugada Syndrome-related Kcnd3Mutations Increase I_to,f Via Augmenting Membrane Expression And Altering Kinetics Of Cardiac Kv4.3Channel

Aim：Cardiac potassium channel KV4.3encoded by gene KCND3formsa tetramer complex with KChIP2subunit, which encodes the fast transientoutward K+current (Ito,f) and this current determines the phase1repolarization of action potential. Brugada syndrome (BrS) is an inheritedcardiac disease featured by abnormal electrocardiogram (ECG) and fatalarrhythmias. Recent study has linked two novel gain-of-function mutations inKCND3to BrS. However, the underlying mechanism remains largelyunknown. The aim of this study is to elucidate the mechanisms for thephenotype caused by both mutations.Method: We engineered both mutations on rat KCND3as G581R(correspond to human G600R) and L450F. Whole cell voltage clamp wasused to determine the effect of the BrS related mutations on K+currentencoded by KV4.3. Western blot and immunofluorescence confocalmicroscopy studies were undertaken to assess the total and membraneexpression of KV4.3of wild type channel and the mutants. RT-PCR wasutilized to study the transcriptional level of KV4.3.Results: While expressed with KChIP2subunit or alone, both mutantssignificantly increased the total and membrane expression of KV4.3, as well asIto,f, compared with wild type. Both mutants demonstrated significantly slower inactivation compared with wild type when expressed with KChIP2.Additionally, while expressed alone, compared with KV4.3-WT, bothKV4.3-G581R and KV4.3-L450F accelerated the recovery from inactivation.Conclusion: Our study revealed that both of the BrS related novelKCND3mutations can increase Ito,fvia increasing the functional expressionand altering the kinetics of KV4.3, while KChIP2also plays an important rolein the pathogenesis of BrS caused by these mutations..