[Contribution to the study of endolymph homeostasis].

The secretory structures of the cochlea including stria vascularis and spiral ligament are responsible for the secretion of endolymph, a fluid characterized by a high potassium concentration [150-180 mM], a low sodium concentration [< 1 mM] and a positive potential [80-100 mV]. This intra-cellular-like fluid fills the endolymphatic compartment and is essential in the transduction process which takes place in the organ of Corti. Yet, the mechanisms which control the homeostasis of this fluid remain largely unknown. To approach this issue we investigated the possibility of a steroid synthesis by the rat cochlea which might modulate the secretion of endolymph. Results show that inner ear expresses mARN encoding some of the enzymes of the steroid pathways. We also investigated the presence of the gastric H+, K(+)-ATPase pump. Results from RT-PCR show that the gastric H+, K(+)-ATPase alpha and beta subunits are expressed in the rat inner ear-lateral wall, organ of Corti and spiral ganglion neurons. The presence of the alpha subunit in inner ear was confirmed by immunoblot. Immunohistochemistry localized this protein in the intermediate cells of the stria vascularis, in the spiral ligament and in spiral ganglion neurons. Along with the vacuolar H(+)-ATPase, the gastric H+, K(+)-ATPase could be involved in the maintenance of H+ equilibrium in endolymph. All these arguments suggest that among the various types of so-called "sensorineural" deafness, some entities including some forms of congenital hearing loss and diuretic-induced ototoxic deafness should be classified as endolymphatic deafness. Such identification seems necessary since these entities result from different pathogenetic mechanisms and might benefit from the development of new therapies.