Abstract Body (Do not enter title and authors here): Introduction: Kv4.3 encoded by KCND3 is an α-subunit of the I_to channel and is highly expressed in both brain and heart. Several KCND3 variants have been shown to be related to inherited arrhythmias and neurological disorders. We have reported a gain-of-function (GOF) KCND3 variant, p.G306A, which was identified in a young patient with early repolarization syndrome (ERS) and refractory epilepsy (RE). The variant increased peak current densities and slowed inactivation of I_to. Micromolar quinidine inhibited increased I_to and accelerated its delayed inactivation. In addition, administration of quinidine to our patient prevented his lethal arrhythmia and epileptic attack. Thus, the suppression of increased I_to can be an effective treatment for ERS and RE. However, it remains unknown if other medicine except for quinidine is effective to suppress the GOF effect on I_to.
Hypothesis: Selective serotonin reuptake inhibitor, fluoxetine which has inhibitory effect for I_to normalizes the GOF effect caused by KCND3 variants.
Aims: To utilize the fluoxetine for the treatment of ERS and RE, we aimed to elucidate the pharmacological effect of fluoxetine on Kv4.3-G306A comparing those to Kv4.3-wild type (WT).
Methods: Plasmids with Kv4.3 WT or G306A were transiently transfected to Chinese Hamster Ovary cells with KChIP2, and reconstituted I_to was measured using whole-cell patch-clamp method at 37⁰C degrees. Fluoxetine loading at 1-100 µM was applied externally.
Results: The peak current densities of I_to at +50 mV were 135.7±19.8 for WT and 321.0±116.7 pA/pF for G306A, and they were decreased to 101.1±20.9 and 199.6±63.6 pA/pF by application of 20 µM fluoxetine (Figure A and B). Fluoxetine inhibited I_to peak current with IC₅₀ of 41.6±7.1 µM for WT and 83.7±16.7 µM for G306A. Although the inactivation in G306A was significantly slower than WT, they were almost normalized after 20 µM fluoxetine application (Figure A and Table). The inhibition effect of fluoxetine was concentration dependent for both peak current densities and inactivation time constants.
Conclusion: Fluoxetine rescued the GOF effect on I_to reconstituted by KCND3 G306A variant, suggesting that fluoxetine could be an effective therapeutic for ERS and RE.