Ion transports in the middle ear epithelium.

Ion transports in the middle ear epithelium have been recently characterized. Experimental data using cell culture have found the existence of a sodium transepithelial transport that drives a water flow. This is thought to play a key role in the maintain of air-filled and fluid-free cavities. Impairment of this process is involved in the pathogenesis of secretory otitis media, which is the main cause of acquired hearing loss. Several modulations of this transport have been evidenced: (i) reactive oxygen species induced an endogenous synthesis of prostaglandin E2 (PGE2), which in turn increased the cAMP level and modulated ion transport rate; (ii) steroids increased the expression of the alpha 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 alpha epithelial sodium channel subunit mRNA level. These modulations may explain the course of middle ear pathology. However, the development of an in vivo model has become mandatory to assess the relevance of these data in the pathophysiology of the middle ear.