title: Evidence for an ATP-dependent bile acid transport protein other than the canalicular liver ecto-ATPase in rats.
abstract: OBJECTIVE
  Canalicular secretion is rate limiting in overall blood-to-bile transport of bile acids. Studies using transfected cells have implicated the canalicular ecto-adenosine triphosphatase (ecto-ATPase) in adenosine triphosphate (ATP)-dependent bile acid transport. However, the structural features of this ecto-ATPase are not those anticipated for an in-to-out ATP-dependent transporter. The aim of this study was to explore the possible existence of an ATP-dependent bile acid transport mechanism distinct from ecto-ATPase.
  
  
  METHODS
  Bile acid transport activity and ecto-ATPase expression were analyzed in primary rat hepatocytes, rat hepatoma HTC cells, and specially adapted HTC (HTC-R) cells using plasma membrane vesicles and Northern blot, slot blot, ribonuclease protection assay, and Western blot analyses.
  
  
  RESULTS
  Plasma membranes isolated from HTC-R cells exhibited ATP-dependent taurocholate transport, which was many-fold greater than that in HTC cells. Hepatocytes showed the highest transport rates. Protein and RNA analyses showed very low expression of ecto-ATPase in HTC and HTC-R cells compared with hepatocytes. There was no difference between the two cell types at both the RNA and protein level.
  
  
  CONCLUSIONS
  These findings show the presence in HTC-R cells and, apparently in hepatocytes, of one or more proteins other than the ecto-ATPase that mediate ATP-dependent transport of bile acids.
authors.affiliation: Department of Medicine, University of California, San Francisco 94143-0538, USA.
authors.forename: T T
authors.initials: TT
authors.lastname: Luther
authors.forename: P
authors.initials: P
authors.lastname: Hammerman
authors.forename: C M
authors.initials: CM
authors.lastname: Rahmaoui
authors.forename: P P
authors.initials: PP
authors.lastname: Lee
authors.forename: S
authors.initials: S
authors.lastname: Sela-Herman
authors.forename: G S
authors.initials: GS
authors.lastname: Matula
authors.forename: M
authors.initials: M
authors.lastname: Ananthanarayanan
authors.forename: F J
authors.initials: FJ
authors.lastname: Suchy
authors.forename: R R
authors.initials: RR
authors.lastname: Cavalieri
authors.forename: N
authors.initials: N
authors.lastname: Lomri
authors.forename: B F
authors.initials: BF
authors.lastname: Scharschmidt
mesh_terms: D018528:ATP-Binding Cassette Transporters / Q000302:isolation & purification / Q000378:metabolism* / Q000502:physiology; D000251:Adenosine Triphosphatases / Q000378:metabolism* / Q000502:physiology; D000818:Animals; D001647:Bile Acids and Salts / Q000378:metabolism*; D001648:Bile Canaliculi / Q000201:enzymology; D015152:Blotting, Northern; D015153:Blotting, Western; D008114:Liver Neoplasms, Experimental; D051381:Rats; D013656:Taurocholic Acid / Q000378:metabolism; D014407:Tumor Cells, Cultured
chemical_list: D018528:ATP-Binding Cassette Transporters; D001647:Bile Acids and Salts; D013656:Taurocholic Acid; D000251:Adenosine Triphosphatases; C027201:ectoATPase