ATP-dependent para-aminohippurate transport by apical multidrug resistanceprotein MRP2

Background Para-aminohippurate (PAH). a widely used model substrate for org anic anion transport in proximal tubule epithelia, was investigated as a su bstrate for the epical multidrug resistance protein MRP2 (symbol ABCC2). Th is ATP-dependent export pump for anionic conjugates and additional amphiphi lic anions was cloned recently and localized to the apical membrane of prox imal tubules in human and rat kidney. Methods. Membrane vesicles from HEK-MRP2 cells containing recombinant human MRP2 and from control vector-transfected HEK-Co cells were incubated with various concentrations of [H-3]PAH, and the net ATP-dependent transport int o inside-out vesicles was determined. Comparative studies were performed wi th membrane vesicles containing recombinant human MRP1. Results. Transport rates at 10 mu mol/L PAH were 21.9 +/- 1.9 and 1.6 +/- 0 .4 pmol x mg protein(-1) x min(-1) (means +/- SEM, N = 10) with membrane ve sicles from HEK-MRP2 and HEK-Co cells, respectively. The K-m value for PAH was 880 mu mol/L. The high-affinity substrate leukotriene C-4 and the inhib itor of MRP-mediared transport, MK571, inhibited MRP2-mediated transport of PAH (100 nmol/L) with IC50 values of 3.3 and 4.0 mu mol/L, respectively. T he nephrotoxic mycotoxin ochratoxin A inhibited MRP2-mediated PAH transport with an IC50 value of 58 mu mol/L. Ochratoxin A was itself a substrate for MRP2. Conclusions. PAH is a good substrate for the ATP-dependent export pump MRP2 . The localization and function of MRP2 indicate that this unidirectional t ransport protein contributes to the secretion of PAH and other amphiphilic anions into the lumen of kidney proximal tubules.