Oxygen modulates Na1 absorption in middle ear epithelium

Portier, F., T. Van Den Abbeele, E. Lecain, E. Sauvaget, B. Escoubet, P. Tran Ba Huy, and P. Herman. Oxygen modulates Na1 absorption in middle ear epithelium. Am. J. Physiol. 276 (Cell Physiol. 45): C312–C317, 1999.— The physiology of the middle ear is primarily concerned with keeping the cavities air filled and fluid free to allow transmission of the sound vibrations from the eardrum to the inner ear. Middle ear epithelial cells are thought to play a key role in this process, since they actively transport Na1 and water. The PO2 of the middle ear cavities varies from 44 to 54 mmHg in healthy human ears but may be lower in the course of secretory otitis media. The effect of chronic hypoxia on ion transport was investigated on a middle ear cell line using the short-circuit current technique. Chronic hypoxia reversibly decreased the rate of Na1 absorption across the MESV cell line. Although a decrease in cellular ATP content was observed, the decrease of Na1 absorption seemed related to a primary modulation of apical Na1 entry. As revealed by RNase protection assay, the decrease in the rate of apical Na1 entry strictly paralleled the decrease in the expression of transcripts encoding the a-subunit of the epithelial Na1 channel. This effect of oxygen on Na1 absorption might account for 1) the presence of fluid in the middle ear in the course of secretory otitis media and 2) the beneficial effect of the ventilation tube in treating otitis media that allows the PO2 to rise and restores the fluid clearance.