Glucocorticosteroids increase sodium transport in middle ear epithelium

The effect of glucocorticosteroids on ion transport was investigated on a middle ear cell line with the short-circuit current (Isc) technique. Dexamethasone (DXM) produced a dose- and time-dependent increase in Isc. Concentration of half-maximal stimulation was 2.68 x 10(-8) M. This effect was blunted by the glucocorticoid antagonist RU-38486 and was related to Na+ transport, as evidenced by the inhibition induced by 1) apical addition of the Na+ channel inhibitor benzamil (10(-6) M) or 2) substitution of Na+ with N-methylglucamine in the incubation medium. The increase in Na+ transport resulted from a primary modulation of apical Na+ entry, since 1) the Na(+)-K(+)-ATPase activity of cellular homogenates was not modified by corticosteroids and 2) the DXM-induced increase in the ouabain-sensitive uptake of 86Rb was blunted by benzamil. Ribonuclease protection assay revealed 1) a constitutive expression of the mRNA encoding the alpha-subunit of the epithelial Na+ channel and 2) that DXM increased the expression of this transcript. This increase was dose dependent and paralleled changes in transepithelial Na+ transport. This study suggests that a component of the beneficial effect of steroid therapy for the treatment of otitis media might be related to increased fluid clearance.