Meniere's disease is one of the pathological entities characterized by endolymphatic hydrops of the cochlear and vestibular labyrinths. Hydrops can result from an alteration of ion and water transport properties of the epithelial cells bordering the endolymphatic system. Little is known about the cellular basis of the pathologic processes involved because data from normal or pathological conditions are lacking for 1) mechanisms of active secretion and absorption of ions, 2) water permeabilities, and 3) ionic permeabilities (both conductive and non-conductive pathways). This project will continue our study of ion and water transport by further developing in vitro techniques to study extra-sensory epithelia, such as common crus and semicircular canal. Experimentation will be done on mechanisms which cannot be studied in vivo (e.g., potassium and sodium transport without the confounding influence of the sensory structures). We will conduct the investigation on several levels: 1) intact epithelium with cells and junctions considered as one membrane, 2) intact epithelium, but properties of luminal and contraluminal cell membranes distinguished by the use of appropriate drugs and 3) isolated patches of luminal membrane. In the first preparation, both uni-directional, isotopic fluxes of ions and net ionic and water fluxes will be determined; in the latter case, nanoliter samples of collected luminal perfusate will be analyzed for ion content (K, Na, C1, Rb). In the second preparation transmural potentials and resistance will be determined. By eliminating the contribution of the basolateral membrane with high-K solutions or with an appropriate ionophore, the specific properties of the luminal membrane can be inferred. Patch clamp pipets will be used to isolate and characterize the postulated rheogenic potassium pump of the dark cells. Ion and water movement will be distinguished from each other by the use of non-transported markers, such as polyethylene glycol. The transport properties of the vestibular dark cells will be defined. The """"""""histologically less-active"""""""" cells, such as those of the semicircular canals, will be studied to determine their role in endolymph homeostasis. This information will be compared with the in vivo characterizations of ion and water transport in the cochlea, which we are presently studying by techniques complementing those proposed herein.
