SLC4A1 and adenoma: One functional group of transporters to be discussed are Cl−/HCO3− exchangers belonging to the class of SLC (solute carrier) 4 proteins such as AE1 (SLC4A1), AE2 (SLC4A2), and AE3 (SLC4A3) [21, 26], or SLC26 proteins [1] such as DRA (SLC26A3; downregulated in adenoma).