The pH difference (∆pH) between CF and non-CF among these studies is about 0.2–0.65 (Coakley et al., 2003; Pezzulo et al., 2012; Shan et al., 2012; Haggie et al., 2016; Scudieri et al., 2018; Simonin et al., 2019; Gianotti et al., 2020), whereas well-differentiated epithelia with better epithelial polarization and more CFTR expressed in the apical membrane than those of less differentiated epithelia (Sheppard et al., 1994), exhibit larger ∆pH (∼0.5) decreases in CF than non-CF epithelia (Scudieri et al., 2018; Gianotti et al., 2020). The gene discussed is CFTR; the disease is cystic fibrosis.