title: A nucleoside transporter is functionally linked to ectonucleotidases in rat liver canalicular membrane.
abstract: Prevention of nucleoside loss in bile is physiologically desirable because hepatocytes are the main source of nucleosides for animal cells which lack de novo nucleoside biosynthesis. We have demonstrated a Na+ gradient-energized, concentrative nucleoside transport system in canalicular membrane vesicles (CMV) from rat liver by studying [3H]adenosine uptake using a rapid filtration technique. The Na(+)-dependent nucleoside transporter accepts purine, analogues of purine nucleosides and uridine; exhibits high affinity for adenosine (apparent Km, 14 microM); is not inhibited by nitrobenzylthioinosine or dipyridamole, and is present in CMV but not in rat liver sinusoidal membrane vesicles. Adenosine transport in right side-out CMV was substantially greater than with inside-out CMV. CMV also contain abundant ecto-ATPase and ecto-AMPase (5'-nucleotidase). These ectoenzymes were shown to degrade nucleotides into nucleosides which were conserved by the Na(+)-dependent nucleoside transport system.
authors.affiliation: Department of Physiology, Tufts University School of Medicine, Boston, Massachusetts 02111.
authors.forename: M
authors.initials: M
authors.lastname: Che
authors.forename: T
authors.initials: T
authors.lastname: Nishida
authors.forename: Z
authors.initials: Z
authors.lastname: Gatmaitan
authors.forename: I M
authors.initials: IM
authors.lastname: Arias
mesh_terms: D000241:Adenosine / Q000378:metabolism*; D000255:Adenosine Triphosphate / Q000378:metabolism*; D000818:Animals; D002352:Carrier Proteins / Q000378:metabolism*; D002462:Cell Membrane / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism*; D007700:Kinetics; D008099:Liver / Q000201:enzymology / Q000378:metabolism*; D008297:Male; D008565:Membrane Proteins / Q000378:metabolism*; D033703:Nucleoside Transport Proteins; D009705:Nucleosides / Q000494:pharmacology; D009708:Nucleotidases / Q000378:metabolism*; D009711:Nucleotides / Q000494:pharmacology; D011189:Potassium Chloride / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D012965:Sodium Chloride / Q000494:pharmacology
chemical_list: D002352:Carrier Proteins; D008565:Membrane Proteins; D033703:Nucleoside Transport Proteins; D009705:Nucleosides; D009711:Nucleotides; D012965:Sodium Chloride; D011189:Potassium Chloride; D000255:Adenosine Triphosphate; D009708:Nucleotidases; D000241:Adenosine