Characterization of the slow current decay in G551D-CFTR. (A) Acceleration of the slow-phase current decay by the W401G mutation. A continuous recording demonstrates an unequivocal biphasic response upon ATP washout for G551D/W401G-CFTR. The current decay phase was fitted with a single exponential function (red line), yielding a time constant of 17.6 s, which is significantly shorter than that of G551D-CFTR (P < 0.05). (B) Summary of time constant of the slow current decay in different mutants. 31.1 ± 5.3 s (n = 12) for G551D-CFTR, 19.0 ± 3.2 s (n = 8) for G551D/W401G-CFTR, and 31.7 ± 5.9 s (n = 12) for G551D/Y1219G-CFTR. Mean ± SEM is shown.