Mediates the Na(+)-independent uptake of organic anions ( ). Shows broad substrate specificity, can transport both organic anions such as bile acid taurocholate (cholyltaurine) and conjugated steroids (dehydroepiandrosterone 3-sulfate, 17-beta-glucuronosyl estradiol, and estrone 3-sulfate), as well as eicosanoids (prostaglandin E2, thromboxane B2, leukotriene C4, and leukotriene E4), and thyroid hormones (T4/L-thyroxine, and T3/3,3',5'-triiodo-L-thyronine) (     , ). Can take up bilirubin glucuronides from plasma into the liver, contributing to the detoxification-enhancing liver-blood shuttling loop . Involved in the clearance of endogenous and exogenous substrates from the liver (, ). Transports coproporphyrin I and III, by-products of heme synthesis, and may be involved in their hepatic disposition . May contribute to regulate the transport of organic compounds in testes across the blood-testis-barrier (Probable). Can transport HMG-CoA reductase inhibitors (also known as statins), such as pravastatin and pitavastatin, a clinically important class of hypolipidemic drugs ( ). May play an important role in plasma and tissue distribution of the structurally diverse chemotherapeutic drug methotrexate . May also transport antihypertension agents, such as the angiotensin-converting enzyme (ACE) inhibitor prodrug enalapril, and the highly selective angiotensin II AT1-receptor antagonist valsartan, in the liver (, ). Shows a pH-sensitive substrate specificity towards prostaglandin E2 and T4 which may be ascribed to the protonation state of the binding site and leads to a stimulation of substrate transport in an acidic microenvironment . Hydrogencarbonate/HCO3(-) acts as the probable counteranion that exchanges for organic anions .
Subcellular locations: Basolateral cell membrane, Basal cell membrane
Detected in basolateral membranes of hepatocytes . Localized to the basal membrane of Sertoli cells .
Highly expressed in liver, at the basolateral membranes of centrilobular hepatocytes (  ). Expressed in liver (at protein level) . Expressed in fetal liver . Not detected in heart, brain, placenta, lung, skeletal muscle, kidney, pancreas, spleen, thymus, prostate, testis, ovary, small intestine, colon and leukocyte (, ). In testis, primarily localized to the basal membrane of Sertoli cells and weakly expressed in Leydig cells and within the tubules .