SLC22A1 (solute carrier family 22 member 1), also called OCT1, is a 554 amino acid (aa), 70-80kD 12-transmembrane glycoprotein of the SLC22 family of polyspecific organic cation transporters (OCT). SLC22A1 is expressed in epithelial cells and some neurons, with detection on hepatocyte sinusoidal membranes and enterocyte basolateral membranes. It transports selected cations bidirectionally and is inhibited by non-transported cations. Human SLC22A1 shares 78% aa identity with mouse and rat SLC22A1. In humans, three inactive isoforms of 506, 483 and 353 aa, lack C-terminal exons 5, 5 and 6, or 3 and 6, respectively.