The effect of MgPPi can be modulated by altering the ligand–NBD1 interaction. (A) WT channels were exposed to 2 mM MgPPi solution immediately after washout of 2 mM ATP or 50 µM P-ATP. (B) The lock-open efficiency of MgPPi was reduced by the W401G mutation, and P-ATP can partially restore the effectiveness of MgPPi on W401g-CFTR. (C) Summary of data presented in A and B. *, P < 0.01.