Function and mechanism analysis of short QT syndrome related KCNH2 gene variants

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In our short QT syndrome family, we identified double mutations in KCNH2 and SLC4A3 genes. However, the KCNH2-H70Y did not affect IKr channel kinetics, which play an important role in the cardiac action potential. Therefore, we aimed to elucidate the relationship between a SLC4A3 mutation and QTc interval. Because the SLC4A3 gene encodes AE3 protein, which worked as an Cl-/HCO3- exchanger for maintaining intracellular pH (pHi), we examine the pHi of SLC4A3-WT and mutant HEK293 stable cells. We found that mutant cells showed low ability for the H+-equivalent flux and slow exchange speed when extracellular solution changed between physiological salt solution and Cl- free solution. Therefore, the SLC4A3-mutation showed loss-of-function of the channel kinetics.We also studied the AE3 protein expression of total cell lysate, mutant cells showed normal expression with WT cells. Then, we focus our study on the electrophysiological study to check whether the SLC4A3 mutant directly involved in the phase 3 and 4 of cardiac action potential. However, there is no significant difference on the IKs, IK1 and Ikr wild-type (WT) currents, recorded on SLC4A3 WT and mutant HEK293 stable cell lines. In the following, we transfected KCNH2-H70Y plasmid into cells stably expressing SLC4A3 mutant, the IKr channel deactivation time constants were prolonged compared to the WT cells.In conclusion, under the abnormal pHi environment affected by SLC4A3 mutation, KCNH2-H70Y decelerate the IKr deactivation kinetics, which may shorten the cardiac action potential and lead to short QT syndrome.