p-aminohippurate transport at the apical membrane in the OK kidney epithelial cell line

Purpose. We investigated the characteristics of transport of an organic anion, p-aminohippurate (PAH), at the apical membrane in a kidney epithelial cell line OK. Methods. Efflux and uptake of [¹⁴C]PAH across the apical membrane were measured using OK cell monolayers grown on microporous membrane filters. Results. PAH efflux to the apical side was greater than that to the basolateral side and significantly inhibited by probenecid. Diethyl pyrocarbonate (DEPC), an inhibitor of potential-sensitive organic anion transport, significantly decreased PAH efflux to the apical side. Moreover, PAH efflux to the apical side was significantly decreased on incubation with high potassium buffer, as compared with control condition. Extracellular pH and Cl^- had no effect on PAH efflux across the apical membrane. PAH uptake from the apical side was inhibited by various organic anions, and the inhibition patterns of PAH uptake from the apical and basolateral sides by various dicarboxylates were similar. Conclusions. These results suggested that PAH efflux to the apical side in OK cells was mediated by a potential-sensitive transport system, but not by an anion exchanger. Moreover, PAH uptake from the apical side was mediated by a specific transport system, which interacts with various organic anions and dicarboxylates.