Aquaporins are membrane water channel proteins that function mainly in water transfer across cellular membranes. In our present study
we investigated the immunohistochemical distribution of aquaporin 1 (AQP1)
AQP3
AQP4
and AQP5 in the mouse respiratory system by immunofluorescence
immunoperoxidase
and immunoelectron microscopy. AQP3
AQP4
and AQP5 are expressed in epithelial cells
whereas AQP1 is expressed in subepithelial connective tissues and capillaries. In the airway surface epithelia from the nasal cavity to the intrapulmonary bronchioles
AQP5 was found to be mainly localized to the luminal side and both AQP3 and AQP4 to the abluminal side. In the alveolar epithelium
AQP5 is localized to the apical membranes of both type I and type II alveolar cells. Compared with the previous studies on the rat respiratory system
in which AQP5 is restricted to the alveolar type I cells and absent from the airway surface epithelia
we found that AQP5 in the mouse is much more widely distributed throughout the surface epithelia. These results suggest that AQP5 has a critical role in water-handling
such as the maintenance of airway surface liquid and clearance of alveolar fluid in the mouse respiratory system. c 2009 The Japan Society of Histochemistry and Cytochemistry.
