title: Role of human organic anion transporter 4 in the transport of ochratoxin A.
abstract: The purpose of this study was to investigate the characteristics of ochratoxin A (OTA) transport by multispecific human organic anion transporter 4 (hOAT4) using mouse proximal tubule cells stably transfected with hOAT4 (S(2) hOAT4). Immunohistochemical analysis revealed that hOAT4 protein was localized to the apical side of the proximal tubule. S(2) hOAT4 expressed hOAT4 protein in the apical side as well as basolateral side and the cells were cultured on the plastic dish for experiments. S(2) hOAT4 exhibited a time- and concentration-dependent, and a saturable increase in OTA uptake, with an apparent K(m) value of 22.9+/-2.44 microM. The OTA uptakes were inhibited by several substrates for the OATs. Probenecid, piroxicam, octanoate and citrinin inhibited OTA uptake by hOAT4 in a competitive manner (K(i)=44.4-336.4 microM), with the following order of potency: probenecid > piroxicam > octanoate >citrinin. The efflux of OTA by S(2) hOAT4 was higher than that by mock. Addition of OTA resulted in slight decrease in viability of S(2) hOAT4 compared with mock. These results indicate that hOAT4 mediates the high-affinity transport of OTA on the apical side of the proximal tubule, whereas the transport characteristics of OTA are distinct from those by basolateral OATs.
authors.affiliation: Department of Pharmacology and Toxicology, Kyorin University School of Medicine, 6-20-2 Shinkawa, Mitaka, Tokyo 181-8611, Japan.
authors.forename: Ellappan
authors.initials: E
authors.lastname: Babu
authors.forename: Michio
authors.initials: M
authors.lastname: Takeda
authors.forename: Shinichi
authors.initials: S
authors.lastname: Narikawa
authors.forename: Yukari
authors.initials: Y
authors.lastname: Kobayashi
authors.forename: Atsushi
authors.initials: A
authors.lastname: Enomoto
authors.forename: Akihiro
authors.initials: A
authors.lastname: Tojo
authors.forename: Seok Ho
authors.initials: SH
authors.lastname: Cha
authors.forename: Takashi
authors.initials: T
authors.lastname: Sekine
authors.forename: Dhanapal
authors.initials: D
authors.lastname: Sakthisekaran
authors.forename: Hitoshi
authors.initials: H
authors.lastname: Endou
mesh_terms: D000818:Animals; D001693:Biological Transport, Active / Q000187:drug effects; D002478:Cells, Cultured; D006801:Humans; D007150:Immunohistochemistry; D007668:Kidney / Q000378:metabolism; D027381:Liver-Specific Organic Anion Transporter 1; D051379:Mice; D009793:Ochratoxins / Q000493:pharmacokinetics*; D029362:Organic Anion Transporters, Sodium-Independent / Q000235:genetics / Q000378:metabolism*; D010894:Piroxicam / Q000494:pharmacology; D011339:Probenecid / Q000494:pharmacology; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D014162:Transfection
chemical_list: D027381:Liver-Specific Organic Anion Transporter 1; D009793:Ochratoxins; D029362:Organic Anion Transporters, Sodium-Independent; D011994:Recombinant Proteins; C498886:SLC22A9 protein, human; C498887:Slco1b2 protein, mouse; D010894:Piroxicam; C025589:ochratoxin A; D011339:Probenecid