Identification of a post-hydrolytic state by AMP-PNP. Macroscopic current of WT-CFTR channels was activated by ATP to a steady state before carrying out similar ligand-exchange protocols as shown in Fig. 2: (A) washout for 10 s and before applying AMP-PNP; (B) directly switched to a 1-s AMP-PNP pulse; and (C) washout for 3 s and before applying a 1-s AMP-PNP pulse.