title: Functional characterization of PCFT/HCP1 as the molecular entity of the carrier-mediated intestinal folate transport system in the rat model.
abstract: Proton-coupled folate transporter/heme carrier protein 1 (PCFT/HCP1) has recently been identified as a transporter that mediates the translocation of folates across the cellular membrane by a proton-coupled mechanism and suggested to be the possible molecular entity of the carrier-mediated intestinal folate transport system. To further clarify its role in intestinal folate transport, we examined the functional characteristics of rat PCFT/HCP1 (rPCFT/HCP1) expressed in Xenopus laevis oocytes and compared with those of the carrier-mediated folate transport system in the rat small intestine evaluated by using the everted tissue sacs. rPCFT/HCP1 was demonstrated to transport folate and methotrexate more efficiently at lower acidic pH and, as evaluated at pH 5.5, with smaller Michaelis constant (K(m)) for the former (2.4 microM) than for the latter (5.7 microM), indicating its characteristic as a proton-coupled folate transporter that favors folate than methotrexate as substrate. rPCFT/HCP1-mediated folate transport was found to be inhibited by several but limited anionic compounds, such as sulfobromophthalein and sulfasalazine. All these characteristics of rPCFT/HCP1 were in agreement with those of carrier-mediated intestinal folate transport system, of which the K(m) values were 1.2 and 5.8 microM for folate and methotrexate, respectively, in the rat small intestine. Furthermore, the distribution profile of the folate transport system activity along the intestinal tract was in agreement with that of rPCFT/HCP1 mRNA. This study is the first to clone rPCFT/HCP1, and we successfully provided several lines of evidence that indicate its role as the molecular entity of the intestinal folate transport system.
authors.affiliation: Department of Biopharmaceutics, Graduate School of Pharmaceutical Sciences, Nagoya City University, Mizuho-ku, Nagoya 467-8603, Japan.
authors.forename: Katsuhisa
authors.initials: K
authors.lastname: Inoue
authors.forename: Yasuhiro
authors.initials: Y
authors.lastname: Nakai
authors.forename: Sayaka
authors.initials: S
authors.lastname: Ueda
authors.forename: Shunsuke
authors.initials: S
authors.lastname: Kamigaso
authors.forename: Kin-ya
authors.initials: KY
authors.lastname: Ohta
authors.forename: Mai
authors.initials: M
authors.lastname: Hatakeyama
authors.forename: Yayoi
authors.initials: Y
authors.lastname: Hayashi
authors.forename: Masaki
authors.initials: M
authors.lastname: Otagiri
authors.forename: Hiroaki
authors.initials: H
authors.lastname: Yuasa
mesh_terms: D000818:Animals; D027321:Anion Transport Proteins / Q000235:genetics / Q000502:physiology*; D001693:Biological Transport, Active; D015152:Blotting, Northern; D018076:DNA, Complementary / Q000096:biosynthesis / Q000235:genetics; D003627:Data Interpretation, Statistical; D005492:Folic Acid / Q000378:metabolism*; D005493:Folic Acid Antagonists / Q000378:metabolism / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D007413:Intestinal Mucosa / Q000378:metabolism*; D007421:Intestine, Small / Q000187:drug effects / Q000378:metabolism; D008727:Methotrexate / Q000378:metabolism / Q000494:pharmacology; D009865:Oocytes; D058979:Proton-Coupled Folate Transporter; D051381:Rats; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014982:Xenopus laevis
chemical_list: D027321:Anion Transport Proteins; D018076:DNA, Complementary; D005493:Folic Acid Antagonists; D058979:Proton-Coupled Folate Transporter; C525126:Slc46a1 protein, rat; D005492:Folic Acid; D008727:Methotrexate