Table 1.

Distribution, physiologic function, and substrate specificity of human multidrug resistance proteins.

MRPs	Location	Physiologic function	Substrate specificity	References
MRP1	Ubiquitous	Efflux of a diverse range of endogenous substances and xenobiotics	Organic anions and steroid conjugates	He et al., 2011
MRP2	Liver, kidney, and gut	Excretion of bilirubin glucuronides into bile and xenobiotics into the intestinal lumen	Organic anions	He et al., 2011
MRP3	Liver, adrenal, pancreas, kidney, and gut	Acts as a protective mechanism when MRP2 is absent or nonfunctional. Also plays an important role in the enterohepatic circulation of endogenous compounds such as bile salts	Organic anions and monoanionic bile acids	Kruh and Belinsky, 2003
MRP4	Prostate, lung, muscle, pancreas, testis, ovary, bladder, and gallblader	Mediation of the extrusion of cAMP and cGMP in urine	Organic anions, cAMP, cGMP, and steroid conjugates	Maher et al., 2005
MRP5	Ubiquitous	Mediation of the extrusion of cAMP and cGMP in urine	Organic anions and cyclic nucleotides	Maher et al., 2005
MRP6	Liver and Kidney	Plays a vital constitutive housekeeping role in normal and abnormal hepatocytes.	Lipophilic anions	Madon et al., 2000
MRP7	Heart, liver, skeletal muscle, and kidney	Involved in phase III (cellular extrusion) of detoxification	Lipophilic anion	Chen et al., 2003
MRP8	Liver	Unknown	Cyclic nucleotides	Yabuuchi et al., 2002
MRP9	Breast tissue and testis	Unknown	Unknown	Yabuuchi et al., 2002