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 previousl y been characterized. The presence of NO synthase (NOS) transcripts was dem onstrated using RNA amplification by reverse transcriptase-polymerase chain reaction in rat middle ear mucosa and in rat primary cultured middle ear e pithelial cells. The expression of NOS was indirectly assessed by nitrite m easurement in the supernatant of primary cultured cells. The effect of NO o n ion transport was investigated in a previously described middle ear epith elial cell line using the short-circuit current (I-sc) tecnique. NO per sc had no effect on I-sc. However, previous work has shown that sodium transpo rt is stimulated by reactive oxygen species (ROS). NO blunted this stimulat ion, 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 res ponsible fur an inhibition of ion transport via peroxynitrite formation.