Organic cation transporters (OCT) are expressed in the plasma membrane of epithelial cells from a wide range of tissues, where they function in the elimination of endogenous amines, cationic drugs and other xenobiotics. The structure of OCTs consists of a 12-transmembrane-domain structure and a large extracellular hydrophilic loop. In humans, OCT1 is primarily expressed in the liver, while OCT2 is expressed in the kidney. OCT3 is expressed in the placenta, skeletal muscle, prostate, aorta and liver. OCT2, also known as SLC22A2, is a multi-specific transporter protein localizing to the basolateral and luminal membranes of the kidney distal tubule and proximal tubules. OCT2 is responsible for mediating the pH-sensitive tubular uptake of organic compounds from circulation. An additional splice variant exists for OCT2, namely OCT2-A.