title: Identification and properties of a novel variant of NBC4 (Na(+)/HCO(3)- co-transporter 4) that is predominantly expressed in the choroid plexus.
abstract: Secretion of HCO(3)- at the apical side of the epithelial cells of the choroid plexus is an essential step in the formation of cerebrospinal fluid. Anion conductance with a high degree of HCO(3)- permeability has been observed and suggested to be the major pathway for HCO(3)- transport across the apical membrane. Recently, it was found that NBC (Na(+)/HCO(3)- co-transporter) 4, an electrogenic member of the NBC family, was expressed in the choroid plexus. We found that a novel variant of the NBC4 [NBC4g/Slc4a5 (solute carrier family 4, sodium bicarbonate co-transporter, member 5)] is almost exclusively expressed in the apical membrane of rat choroid plexus epithelium at exceptionally high levels. RNA interference-mediated knockdown allowed the functional demonstration that NBC4g is the major player in the HCO(3)- transport across the apical membrane of the choroid plexus epithelium. When combined with a recent observation that in choroid plexus epithelial cells electrogenic NBC operates with a stoichiometry of 3:1, the results of the present study suggest that NBC4g mediates the efflux of HCO(3)- and contributes to cerebrospinal fluid production.
authors.affiliation: Department of Biological Sciences, Tokyo Institute of Technology, 4259-B19 Nagatsuta-cho, Midori-ku, Yokohama 226-8501, Japan.
authors.forename: Hidekazu
authors.initials: H
authors.lastname: Fukuda
authors.forename: Taku
authors.initials: T
authors.lastname: Hirata
authors.forename: Nobuhiro
authors.initials: N
authors.lastname: Nakamura
authors.forename: Akira
authors.initials: A
authors.lastname: Kato
authors.forename: Katsumasa
authors.initials: K
authors.lastname: Kawahara
authors.forename: Shigeo
authors.initials: S
authors.lastname: Wakabayashi
authors.forename: Min-Hwang
authors.initials: MH
authors.lastname: Chang
authors.forename: Michael F
authors.initials: MF
authors.lastname: Romero
authors.forename: Shigehisa
authors.initials: S
authors.lastname: Hirose
mesh_terms: D000818:Animals; D001639:Bicarbonates / Q000378:metabolism; D002831:Choroid Plexus / Q000378:metabolism*; D057809:HEK293 Cells; D006367:HeLa Cells; D006801:Humans; D017136:Ion Transport; D008297:Male; D051381:Rats; D017208:Rats, Wistar; D027982:Sodium-Bicarbonate Symporters / Q000235:genetics* / Q000378:metabolism
chemical_list: D001639:Bicarbonates; C422004:Slc4a4 protein, rat; D027982:Sodium-Bicarbonate Symporters