Definition:

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 (17-beta-glucuronosyl estradiol, dehydroepiandrosterone sulfate (DHEAS), and estrone 3-sulfate), as well as eicosanoid leukotriene C4, prostaglandin E2 and L-thyroxine (T4). Hydrogencarbonate/HCO3(-) acts as the probable counteranion that exchanges for organic anions. Shows a pH-sensitive substrate specificity towards sulfated steroids, taurocholate 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. Involved in the clearance of bile acids and organic anions from the liver. Can take up bilirubin glucuronides from plasma into the liver, contributing to the detoxification-enhancing liver-blood shuttling loop. Transports coproporphyrin I and III, by-products of heme synthesis, and may be involved in their hepatic disposition. Can transport HMG-CoA reductase inhibitors (also known as statins) such as pitavastatin, a clinically important class of hypolipidemic drugs. May play an important role in plasma and tissue distribution of the structurally diverse chemotherapeutic drugs methotrexate and paclitaxel. 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.