An
organic anion-transporting polypeptide (OATP) is a
membrane transport protein or 'transporter' that mediates the transport of mainly organic
anions across the
cell membrane. Therefore OATPs are present in the lipid bilayer of the cell membrane, acting as the cell's gatekeepers. OATPs belong to the
Solute Carrier Family (SLC), more specifically the Solute Carrier Organic Anion (SLCO) gene subfamily