MODULATION OF MIDDLE-EAR EPITHELIAL FUNCTION BY STEROIDS - CLINICAL RELEVANCE

The efficacy of steroid therapy for the treatment of otitis media in c hildren remains controversial, and a putative modulation of the middle ear epithelial function has to be demonstrated. Using the MESV cell l ine, short-circuit current (I-SC) technique was used to evaluate chang es in ion transport induced by glucocorticoids. Dexamethasone (DXM) pr oduced a dose- and time-dependent increase in I-SC in MESV cells. This effect was inhibited by specific glucocorticoid antagonist (RU-38486) and was related to a sodium transport, since the DXM-induced increase in I-SC could be prevented or abolished i) by apical addition of the specific Na+ channel inhibitor benzamil; or ii) by substitution of sod ium with N-Methyl-glucamine in the incubation medium. RNase protection assay revealed that DXM increased the expression of the a subunit sod ium channel mRNA, which changes paralleled the modulation of ion trans port. These data demonstrate that steroids up-regulate the trans-epith elial sodium transport in the middle ear epithelium. As far as these e xperimental data can be extrapolated to the in vivo situation, a compo nent of the beneficial effect of steroid therapy for the treatment of otitis media may result from a corticosteroid-induced improvement in f luid clearance from the middle ear.