title: Localization of the Sodium-Taurocholate cotransporting polypeptide in membrane rafts and modulation of its activity by cholesterol in vitro.
abstract: BACKGROUND
  The relevance of discrete localization of hepatobiliary transporters in specific membrane microdomains is not well known.
  
  
  OBJECTIVE
  To determine whether the Na+/taurocholate cotransporting polypeptide (Ntcp), the main hepatic sinusoidal bile salt transporter, is localized in specific membrane microdomains.
  
  
  METHODS
  Presence of Ntcp in membrane rafts obtained from mouse liver was studied by immunoblotting and immunofluorescence. HEK-293 cells stably transfected with rat Ntcp were used for in vitro studies. Expression, localization and function of Ntcp in these cells were assessed by immunoblotting, immunofluorescence and biotinylation studies and Na+ -dependent taurocholate uptake assays, respectively. The effect of cholesterol depletion/repletion assays on Ntcp function was also investigated.
  
  
  RESULTS
  Ntcp localized primarily to membrane rafts in in vivo studies and localized partially in membrane rafts in transfected HEK-293 cells. In these cells, membrane cholesterol depletion resulted in a shift of Ntcp localization into non-membrane rafts, which correlated with a 2.5-fold increase in taurocholate transport. Cholesterol repletion shifted back part of Ntcp into membrane rafts, and normalized taurocholate transport to values similar to control cells.
  
  
  CONCLUSIONS
  Ntcp localizes in membrane rafts and its localization and function are regulated by membrane cholesterol content. This may serve as a novel regulatory mechanism of bile salt transport in liver.
authors.affiliation: Departamento de Gastroenterologia, Facultad de Medicina, Pontificia Universidad Católica de Chile, Marcoleta 367, 833-0024, Santiago, Chile.
authors.forename: Héctor
authors.initials: H
authors.lastname: Molina
authors.forename: Lorena
authors.initials: L
authors.lastname: Azocar
authors.forename: Meenakshisundaram
authors.initials: M
authors.lastname: Ananthanarayanan
authors.forename: Marco
authors.initials: M
authors.lastname: Arrese
authors.forename: Juan Francisco
authors.initials: JF
authors.lastname: Miquel
mesh_terms: D000818:Animals; D001692:Biological Transport; D015153:Blotting, Western; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D005455:Fluorescent Antibody Technique; D006801:Humans; D008099:Liver / Q000378:metabolism; D008563:Membrane Lipids / Q000378:metabolism*; D051379:Mice; D008810:Mice, Inbred C57BL; D029363:Organic Anion Transporters, Sodium-Dependent / Q000378:metabolism*; D051381:Rats; D027981:Symporters / Q000378:metabolism*
chemical_list: D008563:Membrane Lipids; D029363:Organic Anion Transporters, Sodium-Dependent; D027981:Symporters; C071908:sodium-bile acid cotransporter