Hydrolysis triggers the O1→O2 transition. (A) Four representative traces and amplitude histograms show the gating pattern of R352C-CFTR channel in the presence of 2.75 mM ATP. The events in blue boxes are expanded in Fig. 4 for clearer view. (B and C) Representative traces and amplitude histograms for R352C/E1371S-CFTR in the presence (B) or absence (C) of 2.75 mM ATP. The traces were recorded in 375 mM of pipette and perfusion solution (applied to Figs. 4 and 5 as well). Similar observations were made in three patches.