p-aminohippuric acid transport at renal apical membrane mediated by human inorganic phosphate transporter NPT1

Organic anions are secreted into urine via organic anion transporters acros s the renal basolateral and apical membranes. However, no apical membrane t ransporter for organic anions such as p-amino-hippuric acid (PAH) has Set b een identified. In the present study, we showed that human NPT1, which is p resent in renal apical membrane, mediates the transport of PAH. The K-m val ue for PAH uptake was 2.66 mM and the uptake was chloride ion sensitive. Th ese results are compatible with those reported for the classical organic an ion transport system at the renal apical membrane. PAH transport was inhibi ted by various anionic compounds. Human NPT1 also accepted uric acid, benzy lpenicillin, faropenem, and estradiol-17 beta-glucuronide as substrates. Co nsidering its chloride ion sensitivity, Npt1 is expected to function for se cretion of PAH from renal proximal tubular cells. This is the first molecul ar demonstration of an organic anion transport function for PAH at the rena l apical membrane. (C) 2000 Academic Press.