Modeled Ig of WT hERG1 channels in the presence of extracellular Cd²⁺. (A) Ig in response to the voltage-clamping protocol used in Fig. 12. (B and C) Ig_ON at 0–10 ms and 10–300 ms, respectively. (D and E) Ig_OFF at 300–310 ms and 310–600 ms, respectively. (F) Gating current (Ig) caused by movement of VSD and current conducted by Cd²⁺ (I_Cd) for a 300-ms voltage step to +60 mV, followed by a return to the holding potential of −110 mV. The sum of these two currents produces the gating currents simulated to occur in the presence of Cd²⁺. (G) Currents underlying the initial 2 ms of Ig_OFF (300–302 ms). Major contributors to initial Ig_OFF are Cd²⁺currents (I_Cd) related to transitions between S₁₉–S₂₅ and S₂₄–S₃₀ (black) and between S₅–S₁₅ and S₁₄–S₂₄ (pink). Currents related to VSD movement (red, green, and blue) have a small contribution to initial Ig_OFF but dominate after decay of I_Cd.