Production of Nitric Oxide by the Middle Ear Epithelium and Subsequent Inhibition of Sodium Transport

The production of nitric oxide (NO) within the middle ear has not previously been characterized. The presence of NO synthase (NOS) transcripts was demonstrated using RNA amplification by reverse transcriptase-polymerase chain reaction in rat middle ear mucosa and in rat primary cultured middle ear epithelial cells. The expression of NOS was indirectly assessed by nitrite measurement in the supernatant of primary cultured cells. The effect of NO on ion transport was investigated in a previously described middle ear epithelial cell line using the short-circuit current (I_sc) technique. NO per se had no effect on I_sc. However, previous work has shown that sodium transport is stimulated by reactive oxygen species (ROS). NO blunted this stimulation, an inhibition probably related to the toxicity of peroxynitrite, ONOO^-, a highly reactive compound. These results suggest that NO is produced by middle ear epithelial cells and that, in the presence of ROS, NO may be responsible for an inhibition of ion transport via peroxynitrite formation.