TY - JOUR T1 - Further characterization of the electrogenicity and pH-sensitivity of the human organic anion-transporting polypeptides OATP1B1 and OATP1B3 JF - Molecular Pharmacology JO - Mol Pharmacol DO - 10.1124/mol.110.069971 SP - mol.110.069971 AU - Pablo Martinez-Becerra AU - Oscar Briz AU - Marta R. Romero AU - Rocio I.R. Macias AU - Maria J. Perez AU - Carlos Sancho-Mateo AU - Maria Pilar Lostao AU - Jose M. Fernandez-Abalos AU - Jose J.G. Marin Y1 - 2010/01/01 UR - http://molpharm.aspetjournals.org/content/early/2010/12/22/mol.110.069971.abstract N2 - Organic anion-transporting polypeptides (OATPs) are involved in the liver uptake of many endogenous and xenobiotic compounds, such as bile acids and drugs, respectively. Using Xenopus laevis oocytes and CHO cells expressing rat Oatp1a1 and human OATP1B1 and OATP1B3, the sensitivity of these transporters to extracellular/intracellular pH (pHo/pHi) and changes in plasma membrane potential (ΔΨ) was investigated. In Xenopus laevis oocytes, non-specific plasma membrane permeability increased only at pHo below 4.5. Above this value, both using oocytes and CHO cells, extracellular acidification affected differently the specific transport of taurocholic acid (TCA) and estradiol 17β-D-glucuronide (E217βG) by Oatp1a1 (stimulation), OATP1B1 (inhibition) and OATP1B3 (stimulation). Changes in substrate uptake in the presence of valinomycin (K+-ionophore), CCCP and nigericin (protonophores), amiloride (Na+/H+-inhibitor), and cation replacement in the medium, were studied with fluorescent probes for measuring substrate uptake (CGamF), and changes in pHi (SNARF-4F) and ΔΨ (DilC1(5)). The results suggested that activity of these three carriers is sodium/potassium-independent and differently affected by changes in pHo and ΔΨ: Oatp1a1 was confirmed to be an electroneutral anion exchanger, whereas the function of both OATP1B1 and OATP1B3 was markedly affected by the magnitude of ΔΨ. Moreover, electrophysiological measurements revealed the existence of a net anion influx associated to OATP1B1/OATP1B3-mediated transport of TCA, E217βG and estrone-3-sulphate. Moreover, a leakage of Na+ through OATP1B1 and OATP1B3, which is not coupled to substrate transport was found. In conclusion, these results suggest that OATP1B1 and OATP1B3 are electrogenic transporters whose activity may be strongly affected under circumstances of displacement of local pH. ER -