Some ECL1 mutants exhibit altered rectification. WT-CFTR, K114D-CFTR, and E116R-CFTR currents were generated under a voltage protocol wherein membrane potential was held at 0 mV for 50 ms then ramped from −100 mV to 100 mV over 300 ms with the TEVC technique. Standard ND96 was used as bath solution. Currents are shown after subtraction of background currents (in the absence of 10 µM ISO). Rectification of the I-V relationship (rectification ratio) was quantified as defined in Materials and methods. **, P < 0.01 compared with WT-CFTR. n = 5–7. Mean ± SEM is shown.