Aquaporin-2 in the human endolymphatic sac

Abstract

Objective To detect and localize aquaporin-2 (AQP-2), a water channel regulated by the antidiuretic hormone, in human endolymphatic sac.

Material and Methods Human endolymphatic sacs were sampled during removal of vestibular schwannomas via a translabyrinthine approach. Samples were immediately fixed in 10% formalin (24 h) and embedded in paraffin; in situ hybridization and immunohistochemistry were performed with an AQP-2-specific probe and a polyclonal antibody.

Results Both AQP-2 mRNA and protein were detected in the epithelium of the endolymphatic sac. AQP-2 immunostaining was mainly cytoplasmic, suggesting that most AQP-2 was located in intracellular pools.

Conclusion In the endolymphatic sac, AQP-2 probably participates in the homeostasis of endolymph; the possibility of reducing the volume of endolymph by inhibiting its expression and membranous insertion using an antidiuretic hormone inhibitor represents a new therapeutic approach for the treatment of Ménière's disease.

Keywords:

• antidiuretic hormone
• endolymph
• inner ear
• water channel