Modulation of the reentry frequency by stabilizing the O2 state. Representative traces and amplitude histograms for Cysless/I344C/R352Q-CFTR under these conditions: (A) in the presence of 2.75 mM ATP; (B–C) after MTSET modification, in the absence (B) or presence (C) of 2.75 mM ATP. (D) The trace highlights the O2→O1 transition when 2.75 mM ATP was applied to the patch after witnessing an ATP-independent channel opening. (E) The amplitude of O1 and O2 states of Cysless/I344C/R352Q-CFTR before (the left bar) or after (the right bar) being modified by MTSET. The O1/O2 ratio is 0.6 ± 0.02 (n = 8) before MTSET modification versus 0.68 ± 0.02 (n = 11) after MTSET modification. P < 0.05.