ION TRANSPORTS IN THE MIDDLE-EAR EPITHELIUM

Ion transports in the middle ear epithelium have been recently charact erized. Experimental data using cell culture have found the existence of a sodium transepithelial transport that drives a water flow. This i s thought to play a key role in the maintain of air-filled and fluid-f ree cavities. Impairment of this process is involved in the pathogenes is of secretory otitis media, which is the main cause of acquired hear ing loss. Several modulations of this transport have been evidenced: ( i) reactive oxygen species induced an endogenous synthesis of prostagl andin E-2 (PGE(2)), which in turn increased the cAMP level and modulat ed ion transport rate; (ii) steroids increased the expression of the c u subunit sodium channel mRNA, which changes paralleled the modulation of ion transport in the middle ear epithelium; (iii) moderate hypoxia selectively and reversibly decreased the rate of sodium transport, as a result of a parallel decrease in oc epithelial sodium channel subun it mRNA level. These modulations may explain the course of middle ear pathology. However, the development of an in vivo model has become man datory to assess the relevance of these data in the pathophysiology of the middle ear.