SLC22 transporters in epithelial tissues. SLC22 transporters tend to have 12 transmembrane domains (numbered blue cylinders). SLC22 transporters are mostly expressed in epithelial tissues, such as the proximal tubule of the kidney, hepatocytes, cells of the choroid plexus, and the olfactory epithelium. They tend to be uptake transporters, often expressed on the basolateral (blood) side of the polarized epithelial cell, although certain transporters are expressed on the apical side. Figure adapted from Reference 146. Abbreviations: G, glycosylation sites; P, PKC phosphorylation sites.