Urate anion transport function of URAT1 in renal proximal tubule epithelial cells. Schematic representation of urate reabsorption in the proximal tubule. Urate reabsorption at the apical (luminal) membrane is critically regulated by URAT1. The organic anion transporter URAT1 exchanges tubular lumen urate with anions inside proximal tubular epithelial cells. Potent stimulators of the exchange process include the intracellular organic ions lactate, nicotinate, and the monocarboxylate metabolite of the anti-tuberculous drug pyrazinimde. Certain intracellular inorganic ions, including chloride, also stimulate urate exchange by URAT1 but with lesser potency. As depicted, urate reabsorption is suppressed at the luminal membrane by some drugs, including benzbromarone, probenecid, losartan, and sulfinpyrazone, consistent with their urisouric properties. Other agents. that affect urate reabsorption in the proximal tubule, including furosemide and salicylates, may act partly by regulating URAT1 function.