Three different patterns of functional consequences after MTS modification. (A and B) Neither MTSES nor MTSET altered the current of cysless/T351C channels. (C) Modification of 348C by MTSES decreased the current. (D) MTSET increased ATP-dependent current in cysless/M348C channels. After the removal of ATP, there remained a large amount of ATP-independent current, which disappeared upon the application of 10 µM CFTRinh-172. (E) MTSES reduced the current of cysless/Q353C channels. (F) For cysless/Q353C, the treatment of MTSET had little influence on channel function, but prevented the current decrease in response to MTSES, as in E.