title: Angiotensin II directly regulates intestinal epithelial NHE3 in Caco2BBE cells.
abstract: BACKGROUND
  Angiotensin II (AII) effects on intestinal Na+ transport may be multifactorial. To determine if AII might have a direct effect on intestinal epithelial Na+ transport, we investigated its actions on Na+ transport in human intestinal epithelial Caco2BBE cells.
  
  
  RESULTS
  AII increased apical (brush border) sodium-hydrogen exchanger (NHE)-3, but not NHE2, activity within one hour. Similarly, only apical membrane NHE3 abundance increased at 1-2 hours without any change in total NHE3 protein abundance. From 4-48 hours, AII stimulated progressively larger increases in apical NHE3 activity and surface abundance, which was associated with increases in NHE3 protein expression. At 4-24 hours, NHE3 mRNA increases over baseline expression, suggesting increased gene transcription. This was supported by AII induced increases in rat NHE3 gene promoter-reporter activity. AII induction of NHE3 was blocked by the AII type I receptor antagonist losartan. Acute changes in AII-induced increases in NHE3 exocytosis were blocked by a phospholipase C inhibitor, an arachidonic acid cytochrome P450 epoxygenase inhibitor, as well as phosphatidylinositol 3 kinase (PI3K) inhibitors and Akt inhibitor, partially blocked by a metalloproteinase inhibitor and an EGF (epidermal growth factor) receptor kinase inhibitor, but not affected by an inhibitor of MEK-1 (MAPKK-1, mitogen activated protein kinase kinase-1).
  
  
  CONCLUSIONS
  We conclude that angiotensin II has a direct role in regulating intestinal fluid and electrolyte absorption which may contribute to its overall effects in regulation systemic volume and blood pressure. AII activates several key signaling pathways that induce acute and chronic changes in NHE3 membrane trafficking and gene transcription.
authors.affiliation: Department of Medicine, University of Chicago, Chicago, IL 60637, USA. mmusch@medicine.bsd.uchicago.edu
authors.forename: Mark W
authors.initials: MW
authors.lastname: Musch
authors.forename: Yan Chun
authors.initials: YC
authors.lastname: Li
authors.forename: Eugene B
authors.initials: EB
authors.lastname: Chang