Organic Cation and Zwitterion Transporters (OCTs, OCTNs)

This chapter focuses on organic cation transporter (OCT)1 (SLC22A1), OCT2 (SLC22A2), OCT3 (SLC22A3), zwitterion/OCN (OCTN)1 (SLC22A4), OCTN2 (SLC22A5), and OCT6 also called CT2 (SLC22A16). All these transporters are capable of translocating cationic drugs. OCTN1, OCTN2, and OCT6 are also able to translocate zwitterions including L-carnitine. Due to structural and functional similarities of all SLC22 family members, some considerations concerning substrate recognition and translocation obtained from studies with OCT1–3 may be valid for OCTN1, OCTN2, OCT6, and organic anion transporters (OATs). The chapter provides a comprehensible updated overview in which the current knowledge concerning functional properties, structure function relationships, physiological functions in different organs, roles in drug handling, as well as biomedical implications of OCT1–3, OCTN1, OCTN2, and OCT6 is summarized. Specific emphasis is put on aspects concerning the understanding of how these polyspecific transporters recognize and translocate structurally different drugs and how these drugs may interact at individual transporters.