In day 14 and day 15 explants, robust responses to Amil indicated epithelial sodium channel (ENaC) activity, and responses to FSK and cystic fibrosis (CF) transmembrane regulator (CFTR) inhibitor–172 (CFTRinh-172) indicated CFTR activity (Fig. 3, B to D and H to J), again aligning with previous work (8, 17). The gene discussed is CFTR; the disease is cystic fibrosis.