348C, but not 341C, of TM6 can tightly coordinate Cd²⁺ with 1141C of TM12. (A) An inside-out recording shows that the inhibition of 341C/1141C currents was subject to the continuous presence of Cd²⁺ in the solution. (B) Contrary to that shown in A, for the double mutant 348C/1141C, the current inhibition brought by Cd²⁺ in an inside-out patch was reversed extremely slowly by simple washout, but DTT rapidly restored the current. The current decay phase was fitted with a single exponential function (see Fig. S9 for more details). (C) Summary of the percent inhibition of 348C, 1141C, and 348C/1141C currents by 5 µM Cd²⁺. Mean ± SEM is shown.