title: Functional involvement of RFVT3/SLC52A3 in intestinal riboflavin absorption.
abstract: Riboflavin, also known as vitamin B2, is transported across the biological membrane into various organs by transport systems. Riboflavin transporter RFVT3 is expressed in the small intestine and has been suggested to localize in the apical membranes of the intestinal epithelial cells. In this study, we investigated the functional involvement of RFVT3 in riboflavin absorption using intestinal epithelial T84 cells and mouse small intestine. T84 cells expressed RFVT3 and conserved unidirectional riboflavin transport corresponding to intestinal absorption. Apical [(3)H]riboflavin uptake was pH-dependent in T84 cells. This uptake was not affected by Na(+) depletion at apical pH 6.0, although it was significantly decreased at apical pH 7.4. The [(3)H]riboflavin uptake from the apical side of T84 cells was prominently inhibited by the RFVT3 selective inhibitor methylene blue and significantly decreased by transfection of RFVT3-small-interfering RNA. In the gastrointestinal tract, RFVT3 was expressed in the jejunum and ileum. Mouse jejunal and ileal permeabilities of [(3)H]riboflavin were measured by the in situ closed-loop method and were significantly reduced by methylene blue. These results strongly suggest that RFVT3 would functionally be involved in riboflavin absorption in the apical membranes of intestinal epithelial cells.
authors.affiliation: Dept. of Clinical Pharmacology and Therapeutics, Kyoto Univ. Hospital, Sakyo-ku, Kyoto 606-8507, Japan. ayone@kuhp.kyoto-u.ac.jp.
authors.forename: Hiroki
authors.initials: H
authors.lastname: Yoshimatsu
authors.forename: Atsushi
authors.initials: A
authors.lastname: Yonezawa
authors.forename: Yoshiaki
authors.initials: Y
authors.lastname: Yao
authors.forename: Kumiko
authors.initials: K
authors.lastname: Sugano
authors.forename: Shunsaku
authors.initials: S
authors.lastname: Nakagawa
authors.forename: Tomohiro
authors.initials: T
authors.lastname: Omura
authors.forename: Kazuo
authors.initials: K
authors.lastname: Matsubara
mesh_terms: D000818:Animals; D001693:Biological Transport, Active; D002478:Cells, Cultured; D057809:HEK293 Cells; D006801:Humans; D007082:Ileum / Q000187:drug effects / Q000378:metabolism; D017403:In Situ Hybridization; D007408:Intestinal Absorption / Q000187:drug effects / Q000235:genetics / Q000502:physiology*; D007413:Intestinal Mucosa / Q000378:metabolism; D007583:Jejunum / Q000187:drug effects / Q000378:metabolism; D026901:Membrane Transport Proteins / Q000187:drug effects / Q000235:genetics* / Q000502:physiology*; D008751:Methylene Blue / Q000494:pharmacology; D051379:Mice; D012333:RNA, Messenger / Q000096:biosynthesis / Q000235:genetics; D060888:Real-Time Polymerase Chain Reaction; D012256:Riboflavin / Q000378:metabolism*; D014162:Transfection
chemical_list: D026901:Membrane Transport Proteins; D012333:RNA, Messenger; C548553:SLC52A3 protein, human; D008751:Methylene Blue; D012256:Riboflavin
keywords: intestine; transporter; vitamin B2