R117 forms a salt bridge with E1126 in the open state. (A) Representative single-channel current traces of E1126R-, R117E/E1126R-, R117C-, and R117C/E1126C-CFTR recorded under the same experimental conditions as Fig. 2 and their all-points amplitude histograms (right). (B) Mean burst durations of WT-CFTR and the above mutants. #, P < 0.01 indicates a significant difference between WT- and R117C-CFTR; **, P < 0.01 indicates a significant difference between WT- and E1126R-CFTR, between R117C and R117E/E1126R-CFTR, and between R117C and R117C/E1126C. n.d., no current detected for R117E-CFTR in Xenopus oocytes. n = 4–6 each. (C) Single-channel amplitudes of WT-CFTR and mutants. *, P < 0.05 compared with WT-CFTR. (D) Mean fraction of open burst duration is plotted for each open conductance state of E1126R- and R117E/E1126R-CFTR. Mean ± SEM is shown.