To specifically study CFTR function in the apical membrane of FRT epithelia heterologously expressing F508del‐ and G551D‐CFTR, we measured apical Cl− currents (IClapical) after permeabilising the basolateral membrane with amphotericin B, whereas to study native CFTR, we measured CFTR‐mediated short‐circuit current (Isc) in epithelia of human bronchial epithelial cells from cystic fibrosis patients (genotypes: F508del/F508del and F508del/G551D). The gene discussed is CFTR; the disease is cystic fibrosis.