Organic cation/zwitterions transporters (OCT-OCTN) of the SLC22 family share many structural characteristics with other MFS proteins and have received a great deal of attention because of their role in the handling of common drugs, toxins, and endogenic substances(neurotransmitters, polyamines). OCTs are expressing in many tissues, including kidney, liver, olfactory mucosa, brain, retina, and placenta. At present, 3 OCTs and 3 OCTNs are known. OCTs may be a part of the evolutionary conservative system that protects higher organisms against potentially toxic compounds in the environment. The polypeptide chain consists of 543–557 amino acid residues. The secondary structure of the molecule is characterized by 12 transmembrane helices and intracellular localization of N- and C-termini of the molecule. The large extracellular loop (110 amino acid residues) between helices 1 and 2 contains 3 sites for N-linked glycosylation and 6 conservative cysteine residues. The second large intracellular loop located between helices 6 and 7 contains consensus sites for protein kinase A, C, G and casein kinase 2. The specific sequence [-Ser/Thr]-Ile-Val-Thr-Glu-[Phe/Trp]-[Asp/Asn]-Leu-Val-Cys- before helix 2 is unique for the SLC family. OCT1 and OCT2 have 70 % similarity in the amino acid composition, and 50 % similarity to OCT3. According to the “Remote Sensing and Signaling Hypothesis”, OCTs (especially OCTNs) may function in remote interorgan communication by regulating the levels of signaling molecules and key metabolites between organs and organ-body fluids.