Extracellular nucleotides stimulate Cl- currents in biliary epithelia through receptor-mediated IP3 and Ca2+ release

Amal K. Dutta, Kangmee Woo, R. Brian Doctor, J. Gregory Fitz, Andrew P. Feranchak

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27 Scopus citations

Abstract

Extracellular ATP regulates bile formation by binding to P2 receptors on cholangiocytes and stimulating transepithelial Cl- secretion. However, the specific signaling pathways linking receptor binding to Cl - channel activation are not known. Consequently, the aim of these studies in human Mz-Cha-1 biliary cells and normal rat cholangiocyte monolayers was to assess the intracellular pathways responsible for ATP-stimulated increases in intracellular Ca2+ concentration ([Ca2+] i) and membrane Cl- permeability. Exposure of cells to ATP resulted in a rapid increase in [Ca2+]i and activation of membrane Cl- currents; both responses were abolished by prior depletion of intracellular Ca2+. ATP-stimulated Cl- currents demonstrated mild outward rectification, reversal at ECl-, and a single-channel conductance of ∼17 pS, where E is the equilibrium potential. The conductance response to ATP was inhibited by the Cl- channel inhibitors NPPB and DIDS but not the CFTR inhibitor CFTR inh-172. Both ATP-stimulated increases in [Ca2+] i and Cl- channel activity were inhibited by the P2Y receptor antagonist suramin. The PLC inhibitor U73122 and the inositol 1,4,5-triphosphate (IP3) receptor inhibitor 2-APB both blocked the ATP-stimulated increase in [Ca2+]i and membrane Cl - currents. Intracellular dialysis with purified IP3 activated Cl- currents with identical properties to those activated by ATP. Exposure of normal rat cholangiocyte monolayers to ATP increased short-circuit currents (Isc), reflecting transepithelial secretion. The I sc was unaffected by CFTRinh-172 but was significantly inhibited by U73122 or 2-APB. In summary, these findings indicate that the apical P2Y-IP3 receptor signaling complex is a dominant pathway mediating biliary epithelial Cl- transport and, therefore, may represent a potential target for increasing secretion in the treatment of cholestatic liver disease.

Original languageEnglish (US)
JournalAmerican Journal of Physiology - Gastrointestinal and Liver Physiology
Volume295
Issue number5
DOIs
Publication statusPublished - Nov 2008

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Keywords

  • ATP
  • Cholangiocyte
  • Cl channel
  • Inositol 1,4,5-triphosphate
  • P2Y receptor
  • Purinergic signaling

ASJC Scopus subject areas

  • Gastroenterology
  • Physiology (medical)
  • Physiology
  • Hepatology

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