Localization of aquaporins, water channel proteins, in the mouse eustachian tube

Conclusion. Immunolocalization of the subtypes of water channel proteins, aquaporins (AQPs), was detected in the mouse eustachian tube (ET). AQPs are located continuously from the serous glands and the capillary vessels to the luminal side in the ET epithelium and may play an important role in the transportation of water to the surface of the ET lumen through the epithelium. Objectives. Although the water supply to the surface of the ET lumen is considered to be essential for closing of the ET, the pathway of the water in the ET is not fully understood. Since AQPs, a group of water transport proteins, have been reported to regulate water homeostasis, we examined the location of AQPs in the mouse ET. Materials and methods. Nine subtypes of AQPs were examined in paraffin embedded ETs of adult mice using the avidin-biotin peroxidase complex method of immunohistochemistry. Results. Four subtypes of AQPs were detected in the mouse ET. AQP-1 was detected in fibroblasts, endothelial cells of capillary vessels and cartilage cells. AQP-3 was distinctly detected in the basal membrane of epithelial cells. AQP-4 was detected in the basal membrane of epithelial cells. AQP-5 was expressed in the luminal side of the ET epithelial cells and also in the apical surface of the cells of the serous glands.