Aquaporin-6 expression in rat gastrointestinal tract is upregulated by feeding

Background: Some aquaporins have been identified and partially
characterized in the gastrointestinal tract suggesting their
involvement in fluid and small solutes movements. Here we
studied the presence and localization of aquaporin-6 in some
regions of the rat gastrointestinal tract, given its peculiar function
as an ion selective channel.
Materials and methods: The aquaporin-6 expression along the
gastrointestinal tract was investigated by RT-PCR and immunoblotting,
while its localization by in situ hybridization and
immunohistochemistry. The effect of feeding on the aquaporin-
6 mRNA expression was investigated by quantitative real
time RT-PCR.
Results: RT-PCR and immunoblotting experiments showed
that aquaporin-6 was expressed in all the investigated portions
of the rat gastrointestinal tract. Immunoblotting analysis of
brush border membrane vesicle preparations showed an intense
signal for aquaporin-6 protein. The results of in situ hybridization
experiments demonstrate that aquaporin-6 transcript is
present in the isthmus, neck and basal regions of the stomach
lining, and throughout the crypt-villus axis in both small and
large intestine. In the latter regions, immunohistochemistry
revealed strong aquaporin-6 labelling in the apical membrane of
the surface epithelial cells, while weak or no labelling was
observed in the crypt cells. In the stomach, an intense staining
was observed in mucous neck cells and lower signal in principal
cells and some parietal cells. In addition, jejunal mRNA expression
was specifically stimulated by feeding.
Conclusions: This study provides evidence for the aquaporin-
6 distribution throughout the gastrointestinal tract. Aquaporin-
6 localization at the apical membranes of the superficial epithelial
cells and its upregulation by feeding in the small intestine
suggest its direct involvement in the absorption of water and
anions.