FUNCTIONS OF ATP-BINDING CASSETTE (ABC) TRANSPORTERS

Several types of transporters present in the body control the fate of drugs by affecting uptake, distribution, and elimination processes. Among other functions, these proteins mediate the influx and efflux of endogenous as well as exogenous substances across the membranes of the small intestine, bile duct, and blood-brain barrier. In polypharmacotherapy, ATP-dependent transporters (ATP-binding cassette [ABC] transporters) expressed on the apical membrane of intestinal epithelial cells determine oral bioavailability, intestinal efflux clearance, and drug-drug interactions of certain xenobiotics. P-glycoprotein (Pgp), product of the human MDR1 gene, is one of the most important proteins belonging to the ABC transporter superfamily. The tissue and organ distribution of Pgp significantly affects the uptake of xenobiotics, and interactions of drugs with this protein may alter bioavailability of other drugs that are administered simultaneously. The subfamilies of ATP-dependent efflux transporters are discussed, with emphasis on their functions.