title: Adenosine triphosphate release and purinergic (P2) receptor-mediated secretion in small and large mouse cholangiocytes.
abstract: Adenosine triphosphate (ATP) is released from cholangiocytes into bile and is a potent secretogogue by increasing intracellular Ca²(+) and stimulating fluid and electrolyte secretion via binding purinergic (P2) receptors on the apical membrane. Although morphological differences exist between small and large cholangiocytes (lining small and large bile ducts, respectively), the role of P2 signaling has not been previously evaluated along the intrahepatic biliary epithelium. The aim of these studies therefore was to characterize ATP release and P2-signaling pathways in small (MSC) and large (MLC) mouse cholangiocytes. The findings reveal that both MSCs and MLCs express P2 receptors, including P2X4 and P2Y2. Exposure to extracellular nucleotides (ATP, uridine triphosphate, or 2',3'-O-[4-benzoyl-benzoyl]-ATP) caused a rapid increase in intracellular Ca²(+) concentration and in transepithelial secretion (I(sc)) in both cell types, which was inhibited by the Cl(-) channel blockers 5-nitro-2-(-3-phenylpropylamino)-benzoic acid (NPPB) or niflumic acid. In response to mechanical stimulation (flow/shear or cell swelling secondary to hypotonic exposure), both MSCs and MLCs exhibited a significant increase in the rate of exocytosis, which was paralleled by an increase in ATP release. Mechanosensitive ATP release was two-fold greater in MSCs compared to MLCs. ATP release was significantly inhibited by disruption of vesicular trafficking by monensin in both cell types.
  
  
  CONCLUSIONS
  These findings suggest the existence of a P2 signaling axis along intrahepatic biliary ducts with the "upstream" MSCs releasing ATP, which can serve as a paracrine signaling molecule to "downstream" MLCs stimulating Ca²(+)-dependent secretion. Additionally, in MSCs, which do not express the cystic fibrosis transmembrane conductance regulator, Ca²(+)-activated Cl(-) efflux in response to extracellular nucleotides represents the first secretory pathway clearly identified in these cholangiocytes derived from the small intrahepatic ducts.
authors.affiliation: Department of Pediatrics, University of Texas Southwestern Medical Center, Dallas, TX.
authors.forename: Kangmee
authors.initials: K
authors.lastname: Woo
authors.forename: Meghana
authors.initials: M
authors.lastname: Sathe
authors.forename: Charles
authors.initials: C
authors.lastname: Kresge
authors.forename: Victoria
authors.initials: V
authors.lastname: Esser
authors.forename: Yoshiyuki
authors.initials: Y
authors.lastname: Ueno
authors.forename: Julie
authors.initials: J
authors.lastname: Venter
authors.forename: Shannon S
authors.initials: SS
authors.lastname: Glaser
authors.forename: Gianfranco
authors.initials: G
authors.lastname: Alpini
authors.forename: Andrew P
authors.initials: AP
authors.lastname: Feranchak
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism*; D000818:Animals; D000952:Antigens, Polyomavirus Transforming / Q000235:genetics; D002118:Calcium / Q000378:metabolism; D019005:Cystic Fibrosis Transmembrane Conductance Regulator / Q000502:physiology; D005089:Exocytosis; D051379:Mice; D008807:Mice, Inbred BALB C; D012313:RNA / Q000302:isolation & purification; D018048:Receptors, Purinergic P2 / Q000235:genetics / Q000502:physiology*; D058469:Receptors, Purinergic P2X / Q000235:genetics / Q000502:physiology; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction; D014162:Transfection
chemical_list: D000952:Antigens, Polyomavirus Transforming; D018048:Receptors, Purinergic P2; D058469:Receptors, Purinergic P2X; D019005:Cystic Fibrosis Transmembrane Conductance Regulator; D012313:RNA; D000255:Adenosine Triphosphate; D002118:Calcium
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