Identification of aquaporin 5 (AQP5) within the cochlea: cDNA cloning and in situ localization.

Dysfunction of fluid and electrolyte homeostasis is considered to cause variety of inner ear disorders. One group of candidate proteins that may play a critical role in the inner ear fluid homeostasis is the aquaporins, a family of proteins whose members have well defined roles in fluid transport in variety of organs. This study reports the identification of AQP5, a member of the aquaporin family, within the rat inner ear and its in situ localization. AQP5 was initially identified within rat cochlear RNA via RT-PCR and sequence analysis of the amplified fragments. Immunoblot of cochlear homogenate yielded a predominant AQP5-immunoreactive band of M(r) 35 kDa. The anti-AQP5 immunoreactivity, indicating expression of the AQP5 polypeptide, was localized within the cochlea in situ to the cell types that form the lateral wall of the cochlear duct-the external sulcus (ES) cells and the cells of the spiral prominence. Expression of AQP5 was observed in the apical turn but not the basal turn of the cochlea; nor was it observed in the vestibular neuroepithelia or its supporting cells. The restricted expression of AQP5 to the apical turns of the cochlea suggests its potential role in low frequency hearing. Copyright 1999 Academic Press.