Effect of 50 µM Cd²⁺ on 344C/1141C and 345C/1141C. (A) In an inside-out patch, 50 µM Cd²⁺ inhibited 344C/1141C currents almost to the baseline, but removal of the metal ion results in a slow current relaxation that can be accelerated by DTT. The time constants were obtained by fitting corresponding current relaxation curves with single exponential functions. (B) The current relaxation time constants on 344C/1141C and 344C are similar (P = 0.51 for without DTT and P = 0.26 for with DTT, respectively), indicating introduction of 1141C does not increase the binding affinity of Cd²⁺ to 344C. Thus, position 344 may not be close to position 1141. Mean ± SEM is shown. (C) In an inside-out recording, 5 µM Cd²⁺ induced reversible inhibition on 345C/1141C, suggesting 345C and 1141C are not able to construct a bi-dentate Cd²⁺-binding site.