Aquaporins as potential drug targets for Meniere's disease and its related diseases.

The homeostasis of water in the inner ear is essential for maintaining function of hearing and equilibrium. Since the discovery of aquaporin water channels, it has become clear that these channels play a crucial role in inner ear fluid homeostasis. Indeed, proteins or mRNAs of AQP1, AQP2, AQP3, AQP4, AQP5, AQP6, AQP7 and AQP9 are expressed in the inner ear. Many of them are expressed mainly in the stria vascularis and the endolymphatic sac, which are the main sites of secretion and/or absorption of endolymph. Vasopressin type2 receptor is also expressed there. Water homeostasis of the inner ear is regulated in part via the arginine vasopressin-AQP2 system in the same fashion as in the kidney, and endolymphatic hydrops, a morphological characteristic of Meniere's disease, is thought to be caused by mal-regulation of this system. Therefore, aquaporins appear to be important for the development of novel drug therapies for Meniere's disease and related disorders.