Cd²⁺ enhances I_Cd-out of WT but not D509C or D456C hERG1 channels. (A) Traces for initial 10 ms of Ig_OFF of WT hERG1 channels elicited by return of membrane potential to −110 mV from the indicated V_t. (B and C) Traces for initial 10 ms of Ig_OFF of D509C (B) or D456C hERG1 (C) hERG1 channels elicited by return of membrane potential to −110 mV from the indicated V_t. Current traces for mutant channels are aligned below the traces for WT channels to facilitate comparisons based on measured shifts in the V_1/2 for activation of ionic currents. For all panels, black traces represent control currents, and red traces represent currents after treatment of an oocyte with 0.1 mM (WT channels) or 0.3 mM (mutant channels) CdCl₂.