Ca2+ current involvement in a KCNH2 mutation's phenotype and its modulation by estrogen.

BACKGROUND: Estrogens affect repolarization and may act as phenotype modifiers in long QT syndrome (LQTS). In a LQT2 patient with the G628S-KCNH2 mutation (normal CACNA1C genes) the occurrence of arrhythmia-related symptoms followed 17-β estradiol (E2) administration. This study aims to test whether a mechanistic link can be established between the two events. METHODS: Membrane potential, ICaL and IKr were measured from mutant (LQT2) and wild-type (WT) hiPS-CMs exposed to 10 nM E2. Adequacy of E2 effects in accounting for patient's electrical phenotype was tested by in silico simulations using a "population" approach. Molecular characterization was carried out by qPCR and immunocytochemistry. RESULTS: LQT2 hiPS-CMs were characterized by marked prolongation of action potential duration (APD) and susceptibility to early afterdepolarizations (EADs), thus recapitulating the LQT2 phenotype. In LQT2 hiPS-CMs, IKr was absent, the ICaL window was increased and the recovery from inactivation was delayed. E2 reversed mutation's effects on APD and ICaL window, but failed to restore IKr and reduce EADs prevalence. E2 also introduced a fast component in ICaL recovery which contributed to ICaL availability during the AP plateau. E2 did not change the expression of KCNH2 channels, E2 receptors (GPER) and CaV1.2 channels (CACNA1C). Simulations indicate that the changes in ICaL gating are a major determinant of APD prolongation and EADs associated with the KCNH2 mutation. CONCLUSIONS: The KCNH2 mutation was associated with ICaL gating abnormalities crucially contributing to APD prolongation, which were largely corrected by E2. However, by accelerating ICaL recovery, E2 facilitated EADs despite APD shortening.