Overview of Drug Transporter Families

Transporters are membrane proteins whose primary function is to facilitate the flux of molecules into and out of cells. Because of the involvement of transporters in all facets of drug absorption, tissue distribution, excretion, and efficacy/toxicity, characterization of transporter structure can provide a scientific basis for understanding drug delivery and disposition, as well as the molecular mechanisms of drug interaction and interindividual/interspecies differences. Most drug transporters are expressed in tissues with barrier functions such as the liver, kidney, intestine, placenta, and brain. Cells at the border of these barriers are usually polarized. Drug transporters can be classified in a number of different manners, including as efflux transporters versus influx transporters, secretory transporters versus absorptive transporters, and ATP-binding cassette (ABC) transporters versus solute carrier (SLC) transporters. Regulation of transporter activity at the gene level usually occurs within hours and days and is therefore classified as long-term or chronic regulation.