ATP12A and cystic fibrosis: Figure 2C shows that non-CF and CF epithelia acidify the apical solution after 3 hours. Unexpectedly, acidification was more marked in non-CF epithelia, with pH values close to 6.5 (Figure 2C, left). Inclusion of proton pump inhibitors also led to some unexpected results. In non-CF cells, bafilomycin A1 and ouabain were both effective in partially reducing the acidification, and combination of the 2 compounds had an additive effect. In contrast, CF cells were mostly sensitive to ouabain and not to bafilomycin A1 (Figure 2C, right).