title: Expression and immunolocalization of aquaporin-7 in rat gastrointestinal tract.
abstract: BACKGROUND
  In the gastrointestinal tract of mammals, water can either be secreted with digestive juices or absorbed by the small and large intestine. Transcellular water movement can be mediated by the transmembrane protein family of AQPs (aquaporins), as has also been recently identified in the gastrointestinal tract. However, the localization, expression and functioning of AQPs in the gastrointestinal tract have not been completely characterized. For the present study, we investigated: (1) the expression of AQP7 in some portions of rat gastrointestinal tract by semiquantitative reverse transcriptase-PCR and by immunoblotting and (2) the cellular and subcellular localization of AQP7 by immunohistochemistry.
  
  
  RESULTS
  AQP7 mRNA and proteins were highly expressed in the small intestine, weakly in the caecum, colon and rectum and were absent in the stomach. Immunoblotting analysis using rat gastrointestinal tract membrane fractions showed two major bands corresponding to a molecular mass of approx. 34 and 40 kDa for the AQP7 protein. No bands were observed when the anti-AQP7 antibody was preadsorbed with the immunizing peptide. Immunohistochemistry revealed strong AQP7 labelling in the surface epithelial cells of duodenum, jejunum, ileum, caecum, colon and rectum, whereas weak or no labelling was observed in the crypt cells. The labelling was manifest particularly in the apical membrane but intracellular staining was also observed.
  
  
  CONCLUSIONS
  The results indicate that AQP7 is present in the small and large intestine. The higher expression of AQP7 protein at the apical pole of the superficial epithelial cells suggests its involvement in rapid fluid movement through the villus epithelium.
authors.affiliation: Department of Experimental Medicine, Section of Human Physiology, University of Pavia, Via Forlanini 6, I-27100 Pavia, Italy. lumberto@unipv.it
authors.forename: Umberto
authors.initials: U
authors.lastname: Laforenza
authors.forename: Giulia
authors.initials: G
authors.lastname: Gastaldi
authors.forename: Monica
authors.initials: M
authors.lastname: Grazioli
authors.forename: Emanuela
authors.initials: E
authors.lastname: Cova
authors.forename: Simona
authors.initials: S
authors.lastname: Tritto
authors.forename: Alide
authors.initials: A
authors.lastname: Faelli
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Calamita
authors.forename: Ulderico
authors.initials: U
authors.lastname: Ventura
mesh_terms: D000818:Animals; D020346:Aquaporins / Q000032:analysis / Q000378:metabolism*; D002463:Cell Membrane Permeability; D041981:Gastrointestinal Tract / Q000378:metabolism*; D015151:Immunoblotting; D007150:Immunohistochemistry; D007408:Intestinal Absorption / Q000502:physiology; D007413:Intestinal Mucosa / Q000378:metabolism; D007420:Intestine, Large / Q000378:metabolism; D007421:Intestine, Small / Q000378:metabolism; D016253:Microscopy, Immunoelectron; D012333:RNA, Messenger / Q000032:analysis / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014018:Tissue Distribution; D014867:Water / Q000378:metabolism
chemical_list: C491926:Aqp7 protein, rat; D020346:Aquaporins; D012333:RNA, Messenger; D014867:Water