Inhibition of Cardiac Ion Channels by Sertraline 329 Fig. 2. The effect of sertraline on human ether-a-go-go-related gene (hERG) currents expressed in HEK293 cells. (A) Current responses to step voltage pulses of －80 to ＋50 mV in 10 mV steps from a holding potential of －80 mV (upper panel). Center: absence of sertraline, control condition; lower: in the presence of 1 μM sertraline. (B) Voltage-relationship of the hERG current measured at the end of depolarizing pulses against the pulse potential in the control and 1 μM sertraline. (C) Voltage-relationship of the tail current measured at its peak just after repolarization in control and after application of 1 μM sertraline. Data were fitted using Boltzmann equation. (D) Dose-response relationship for inhibition of hERG currents by serial application of 0.1, 0.3, 1, and 3 μM sertraline (n=4). The relationship was fitted to a Hill equation. The IC50 and Hill coefficient were 0.7 μM and 1.3, respectively. currents. Voltage-dependent effects of sertraline on hERG channels were determined using the protocol shown in the inset of Fig. 2A. Representative hERG current traces in the absence and presence of sertraline (1 μM) are, respectively, shown in Fig. 2A. Both activating currents measured at the end of the depolarizing step (Fig. 2B) and peak tail current amplitude (Fig. 2C) measured following the step to －40 mV were dramatically reduced by sertraline. As demon- strated in Fig. 2D, sertraline concentration-dependently in- hibited hERG channel currents. Sertraline at concen- trations of 1, 3, 10, and 30 μM inhibited the IKr amplitude by 7.9±1.9%, 24.2±1.9%, 60.1±2.7%, and 86.4±1.4%, respec- tively (n=4). A non-linear fitting of the experimental values using Hill’s equation revealed the 50% inhibitory concen- tration (IC50) of sertraline. The IC50 and Hill coefficient were 0.7±0.01 μM and 1.3±0.02, respectively. Fig. 3 shows the effects of sertraline on the slowly activat- ing outward K＋ current (IKs) in KCNQ1/KCNE1 cDNA- transfected HEK293 cells. Sertraline inhibited IKs concen- tration-dependently. Sertraline at concentrations of 1, 3, 10, and 30 μM reduced the IKs amplitude by 1.5±3.8%, 10.3±2.5%, 36.6±3.5%, and 84.0±5.6%, respectively (n=4). The IC50 value calculated from the concentration-response curve was 12.3±1.3 μM, and the Hill coefficient was 2.5±0.1. And we also investigated the effects of sertraline on IK1 in KCNJ2 cDNA-transfected HEK293 cells (Fig. 4). Sertra- line at concentrations of 1, 3, 10, and 30 μM reduced the IK1 amplitude by 0.7±2.7%, 9.4±1.1%, 45.7±3.9%, and 92.5± 1.2%, respectively (n=4). The IC50 value calculated from the concentration-response curve was 10.5±0.5 μM, and the Hill coefficient was 2.1±0.2. Fig. 3. The effect of sertraline on IKs expressed in HEK293 cells. (A) The cells were depolarized to ＋60 mV from a holding potential of －80 mV, followed by a 3-s repolarization back to －40 mV (upper). Representative current traces under control condition and after application of 1, 3, 10, and 30 μM sertraline (lower). (B) Concentration response curve for inhibition of IKs by serial application of 1, 3, 10, and 30 μM sertraline. The relationship was fitted to a Hill equation. The IC50 and Hill coefficient were 12.3 μM and 2.5, respectively (n=4). (C) Voltage-relationship of the peak IKs measured at the end of depolarizing pulses against the pulse potential in the control and 10 μM sertraline (n=4). Fig. 4. The effect of sertraline on IK1 expressed in HEK293 cells. (A) The IK1 was elicited by the voltage of a one-step pulse (lasting 1 s) from －80 mV to －120 mV (upper). Representative current traces under control condition and after application of 1, 3, 10, and 30 μM sertraline (lower). (B) Concentration response curve for inhibition of IK1 by serial application of 1, 3, 10, and 30 μM sertraline. The relationship was fitted to a Hill equation. The IC50 and Hill coefficient were 10.5 μM and 2.1, respectively (n=4). (C) Voltage-relationship of the IK1 measured at the end of hyperpolarizing pulses against the pulse potential in the control and 10 μM sertraline (n=4).