Ivacaftor (10 μM) significantly increases the forskolin-stimulated Cl- secretion (IT) by ~4-fold with an EC50 of 100 nM in the recombinant Fisher rat thyroid (FRT) cells expressing G551D gating mutation of CFTR, and by ~6-fold with an EC50 of 25 nM in the recombinant cells expressing temperature-corrected F508del processing mutation of CFTR. Consistent with the increases in the forskolin-stimulated IT, Ivacaftor