title: Cholangiocyte cilia detect changes in luminal fluid flow and transmit them into intracellular Ca2+ and cAMP signaling.
abstract: OBJECTIVE
  Cholangiocytes have primary cilia extending from the apical plasma membrane into the ductal lumen. While the physiologic significance of cholangiocyte cilia is unknown, studies in renal epithelia suggest that primary cilia possess sensory functions. Here, we tested the hypothesis that cholangiocyte cilia are sensory organelles that detect and transmit luminal bile flow stimuli into intracellular Ca2+ ([Ca2+]i) and adenosine 3',5'-cyclic monophosphate (cAMP) signaling.
  
  
  METHODS
  Scanning electron microscopy, transmission electron microscopy, and immunofluorescent confocal microscopy of rat isolated intrahepatic bile duct units (IBDUs) were used to detect and characterize cholangiocyte cilia. The fluid flow-induced changes in Ca2+ and cAMP levels in cholangiocytes of microperfused IBDUs were detected by epifluorescence microscopy and a fluorescence assay, respectively.
  
  
  RESULTS
  In microperfused IBDUs, luminal fluid flow induced an increase in [Ca2+]i and caused suppression of the forskolin-stimulated cAMP increase. The fluid flow-induced changes in [Ca2+]i and cAMP levels were significantly reduced or abolished when cilia were removed by chloral hydrate or when ciliary-associated proteins polycystin-1 (a mechanoreceptor), polycystin-2 (a Ca2+ channel), and the Ca2+-inhibitable adenylyl cyclase isoform 6 were individually down-regulated by small interfering RNAs.
  
  
  CONCLUSIONS
  Cholangiocyte cilia are sensory organelles containing polycystin-1, polycystin-2, and adenylyl cyclase isoform 6 through which luminal fluid flow affects both [Ca2+]i and cAMP signaling in the cell. The data suggest a new model for regulation of ductal bile secretion involving cholangiocyte cilia.
authors.affiliation: Miles and Shirley Fiterman Center for Digestive Diseases, Department of Internal Medicine, Mayo Clinic College of Medicine, Rochester, Minnesota 55905, USA.
authors.forename: Anatoliy I
authors.initials: AI
authors.lastname: Masyuk
authors.forename: Tatyana V
authors.initials: TV
authors.lastname: Masyuk
authors.forename: Patrick L
authors.initials: PL
authors.lastname: Splinter
authors.forename: Bing Q
authors.initials: BQ
authors.lastname: Huang
authors.forename: Angela J
authors.initials: AJ
authors.lastname: Stroope
authors.forename: Nicholas F
authors.initials: NF
authors.lastname: LaRusso
mesh_terms: D000818:Animals; D001653:Bile Ducts, Intrahepatic / Q000378:metabolism* / Q000648:ultrastructure; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000378:metabolism; D002923:Cilia / Q000378:metabolism / Q000648:ultrastructure; D000242:Cyclic AMP / Q000378:metabolism*; D066298:In Vitro Techniques; D007424:Intracellular Fluid / Q000378:metabolism*; D008297:Male; D008855:Microscopy, Electron, Scanning; D046529:Microscopy, Electron, Transmission; D008856:Microscopy, Fluorescence; D051381:Rats; D011916:Rats, Inbred F344; D015398:Signal Transduction / Q000502:physiology*; D050396:TRPP Cation Channels / Q000378:metabolism
chemical_list: D002118:Calcium; D015220:Calcium Channels; D000242:Cyclic AMP; D050396:TRPP Cation Channels