Figure 11.

Rapid decay of current in A1374C CFTR channels (containing a mid-interface target Cys—in the NBD2 D loop—between the two composite sites) upon ATP washout (w/o) or modification by MTSET⁺. (A and B) A1374C-(C832S-C1458S) CFTR channels were modified by 1 mM MTSET⁺ (red trace bar) either while closed in the absence of ATP (A), as assessed by subsequent diminished ATP-activated current (3 mM, black bars below records), or in the presence of ATP (B). 10 mM DTT (black bars above record) removed the MTSET⁺ adduct after each modification. (B) Colored lines show single-exponential fits to current decay time courses on modification by MTSET⁺ (red, τ_MTS), or on ATP removal (gray, τ_ATPw/o); colored numbers give time constants. (C) Amplitude of residual current (I_residual %), relative to ATP-activated current before modification, for A1374C channels modified, while closed (left, 0 ATP), by 5 µM–1 mM MTSET⁺ (red bar, 9 ± 2%; n = 8 measurements in six patches), or while opening and closing (right, 3 mM ATP), by 10 µM–1 mM MTSET⁺ (red bar, 17 ± 6%, n = 3 measurements in two patches). (D) Average τ_ATPw/o (gray bar, w/o, 1.2 ± 0.6 s; n = 4 measurements in three patches) with corresponding average τ_MTS (red bar, MTSET⁺, 2.5 ± 0.9 s) from the same patches. Error bars represent mean ± SEM.