Influence of the extracellular pH on the transport of para-aminohippurate via organic anion transporter 1

Organic anion transporter 1 (OAT1) is one of the transporters responsible for renal elimination of organic anions. In the present study, the influence of extracellular pH on the transport-activity of OAT1 was examined using OAT1-transfected HEK 293 cells and the model substrate para-aminohippurate (PAH). The uptake of [3H]PAH was measured by a liquid scintillation counter at different time points, varying extracellular pH and chemicals possibly influencing pH-dependent processes. In general, uptake of PAH was higher at lower than at higher extracellular pH. Probenecid fully inhibited PAH uptake regardless of the extracellular pH. At pH 6.4 and pH 7.4, Michaelis-Menten constant remained the same, but Vmax increased. Carbonyl cyanide 3-chlorophenylhydrazone (CCCP) inhibited the uptake of PAH with an IC50 of 2,5 ± 0,5 µM. The pH dependence on the uptake of PAH remained in the presence of CCCP. Hydrogen carbonate has no influence on the uptake of PAH whereas acetazolamide, 4-acetamido-4-isothiocyanostilbene-2,2-disulfonate (SITS) and amiloride inhibited the uptake of PAH at pH 6.4 and 7.4.2015-02-2