Modulation of Middle Ear Epithelial Function by Steroids: Clinical Relevance

Abstract

The efficacy of steroid therapy for the treatment of otitis media in children remains controversial, and a putative modulation of the middle ear epithelial function has to be demonstrated. Using the MESV cell line, short-circuit current (I_sc) technique was used to evaluate changes in ion transport induced by glucocorticoids. Dexamethasone (DXM) produced 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 sodium with N-Methyl-glucamine in the incubation medium. RNase protection assay revealed that DXM increased the expression of the α subunit sodium channel mRNA, which changes paralleled the modulation of ion transport. These data demonstrate that steroids up-regulate the trans-epithelial sodium transport in the middle ear epithelium. As far as these experimental data can be extrapolated to the in vivo situation, a component of the beneficial effect of steroid therapy for the treatment of otitis media may result from a corticosteroid-induced improvement in fluid clearance from the middle ear

Key Words:

• short-circuit current technique
• steroids
• otitis media
• fluid clearance