Expression and localization of aquaporin water channels in rat hepatocytes. Evidence for a role in canalicular bile secretion

Robert C. Huebert, Patrick L. Splinter, Fabiana Garcia, Raul A. Marinelli, Nicholas F. Larusso

Research output: Contribution to journalArticle

122 Scopus citations

Abstract

Although bile formation requires that large volumes of water be rapidly transported across liver epithelia, including hepatocytes, the molecular mechanisms by which water is secreted into bile are obscure. The aquaporins are a family of 10 channel-forming, integral membrane proteins of ∼28 kDa numbered 0-9 that allow water to rapidly traverse epithelial barriers in several organs including kidney, eye, and brain. We found transcripts of three of 10 aquaporins in hepatocytes (aquaporin 8 ≫ aquaporin 9 > aquaporin 0) by reverse transcription-polymerase chain reaction and quantitative ribonuclease protection assays; immunohistochemistry confirmed the presence of these three proteins in liver. Immunoblots of subcellular fractions of hepatocytes showed enrichment of aquaporins 0 and 8 in microsomes and canalicular plasma membranes; aquaporin 9 was enriched only in basolateral plasma membranes. Immunofluorescence of hepatocyte couplets confirmed the intracellular/canalicular localization of aquaporins 0 and 8 and the basolateral localization of aquaporin 9. Upon exposure of couplets to a choleretic stimulus (i.e. dibutyryl cAMP), aquaporin 8 redistributed to the canalicular plasma membrane; the subcellular distributions of aquaporins 0 and 9 were unaffected. In addition, exposure of couplets to dibutyryl cAMP caused an increase in canalicular water transport in the presence and absence of an osmotic gradient, an effect that was blocked by aquaporin inhibitors. These results provide evidence that aquaporins are present in hepatocytes and that aquaporins are involved in agonist-stimulated canalicular bile secretion.

Original languageEnglish (US)
Pages (from-to)22710-22717
Number of pages8
JournalJournal of Biological Chemistry
Volume277
Issue number25
DOIs
StatePublished - Jun 21 2002

ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology
  • Cell Biology

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