title: Regulation of biliary secretion through apical purinergic receptors in cultured rat cholangiocytes.
abstract: To evaluate whether ATP in bile serves as a signaling factor regulating ductular secretion, voltage-clamp studies were performed using a novel normal rat cholangiocyte (NRC) model. In the presence of amiloride (100 microM) to block Na+ channels, exposure of the apical membrane to ATP significantly increased the short-circuit current (Isc) from 18.2 +/- 5.9 to 52.8 +/- 12.7 microA (n = 18). The response to ATP is mediated by basolateral-to-apical Cl- transport because it is inhibited by 1) the Cl- channel blockers 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (1 mM), diphenylanthranilic acid (1.5 mM), or 5-nitro-2-(3-phenylpropylamino)benzoic acid (50 or 100 microM) in the apical chamber, 2) the K+ channel blocker Ba2+ (5 mM), or 3) the Na(+)-K(+)-2Cl- cotransport inhibitor bumetanide (200 microM) in the basolateral chamber. Other nucleotides stimulated an increase in Isc with a rank order potency of UTP = ATP = adenosine 5'-O-(3)-thiotriphosphate, consistent with P2u purinergic receptors. ADP, AMP, 2-methylthioadenosine 5'-triphosphate, and adenosine had no effect. A cDNA encoding a rat P2u receptor (rP2uR) was isolated from a liver cDNA library, and functional expression of the corresponding mRNA in Xenopus laevis oocytes resulted in the appearance of ATP-stimulated currents with a similar pharmacological profile. Northern analysis identified hybridizing mRNA transcripts in NRC as well as other cell types in rat liver. These findings indicate that exposure of polarized cholangiocytes to ATP results in luminal Cl- secretion through activation of P2u receptors in the apical membrane. Release of ATP into bile may serve as an autocrine or paracrine signal regulating cholangiocyte secretory function.
authors.affiliation: Department of Medicine, University of Colorado Health Sciences Center, Denver 80262, USA.
authors.forename: T
authors.initials: T
authors.lastname: Schlenker
authors.forename: J M
authors.initials: JM
authors.lastname: Romac
authors.forename: A I
authors.initials: AI
authors.lastname: Sharara
authors.forename: R M
authors.initials: RM
authors.lastname: Roman
authors.forename: S J
authors.initials: SJ
authors.lastname: Kim
authors.forename: N
authors.initials: N
authors.lastname: LaRusso
authors.forename: R A
authors.initials: RA
authors.lastname: Liddle
authors.forename: J G
authors.initials: JG
authors.lastname: Fitz
mesh_terms: D000255:Adenosine Triphosphate / Q000494:pharmacology*; D000584:Amiloride / Q000494:pharmacology; D000595:Amino Acid Sequence; D000818:Animals; D001646:Bile / Q000378:metabolism*; D001652:Bile Ducts / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D002462:Cell Membrane / Q000502:physiology; D016764:Cell Polarity; D002478:Cells, Cultured; D002712:Chlorides / Q000378:metabolism; D019976:Cloning, Organism; D005260:Female; D006801:Humans; D007473:Ion Channels / Q000037:antagonists & inhibitors; D008099:Liver / Q000378:metabolism; D008564:Membrane Potentials / Q000187:drug effects; D051379:Mice; D008969:Molecular Sequence Data; D009865:Oocytes / Q000502:physiology; D012333:RNA, Messenger / Q000096:biosynthesis; D051381:Rats; D018048:Receptors, Purinergic P2 / Q000096:biosynthesis / Q000737:chemistry / Q000502:physiology*; D058473:Receptors, Purinergic P2Y2; D011994:Recombinant Proteins / Q000096:biosynthesis; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D015398:Signal Transduction; D014158:Transcription, Genetic; D014982:Xenopus laevis
chemical_list: D002712:Chlorides; D007473:Ion Channels; C546385:P2RY2 protein, human; C546386:P2ry2 protein, mouse; C546387:P2ry2 protein, rat; D012333:RNA, Messenger; D018048:Receptors, Purinergic P2; D058473:Receptors, Purinergic P2Y2; D011994:Recombinant Proteins; D000584:Amiloride; D000255:Adenosine Triphosphate