SLC9A3 and adenoma: Interestingly, colonic expression of the genes encoding the apical ion transporters Na+/H+ exchanger 3 (NHE3) and the Cl−/HCO3− exchanger Down-regulated in Adenoma (DRA), which are involved in ion and water re-uptake from the colon were upregulated in GF KO mice (Figure 1D,E).