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Identification and properties of a novel variant of NBC4 (Na+/HCO3 co-transporter 4) that is predominantly expressed in the choroid plexus

Secretion of HCO3 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 HCO3 permeability has been observed and suggested to be the major pathway for HCO3 transport across the apical membrane. Recently, it was found that NBC (Na+/HCO3 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 HCO3 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 HCO3 and contributes to cerebrospinal fluid production.

Authors:   Fukuda H; Hirata T; Nakamura N; Kato A; Kawahara K; Wakabayashi S; Chang M-H; Romero MF; Hirose S
Journal:   Biochemical Journal
Volume:   450
edition:   1
Year:   2013
Pages:   179
DOI:   10.1042/BJ20121515
Publication date:   15-Feb-2013
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