Ussing Chamber Measurements for CFTR Function

Epithelial cells grown to confluence were mounted in modified Ussing chambers. Short-circuit current (Isc) was obtained with an epithelial voltage clamp as described previously (34). Briefly, the mucosal bathing solution was changed to a low Cl^– solution containing 1.2 mM NaCl, 115 mM sodium gluconate, plus 100 μM amiloride followed by addition of agonists (20 μM forskolin, and/or 10 μM ivacaftor) to the mucosal surface. CFTR inhibitor 172 (CFTR_inh-172) (10 μM; Sigma-Aldrich) was added to the bathing solution at the conclusion of each experiment to block CFTR-dependent Isc.