Effects of cysteine substitutions on single-channel current amplitude. (A) Single-channel traces for cysless/WT and two cysteine-substituted mutants. Single-channel amplitude: cysless/WT, 0.46 ± 0.005 pA (n = 5); cysless/K355C, 0.28 ± 0.011 pA (n = 4); cysless/F337C, 0.19 ± 0.008 pA (n = 3). (B) Summary of the single-channel amplitude for cysless/WT and all mutant channels. The data are shown as mean and SEM of three to seven experiments. Stars indicate a significant difference in the single-channel amplitude from the cysless/WT, as determined by Student’s t test. Daggers indicate channels whose single-channel amplitude is too small and/or variable to be measured accurately.