LOCALIZATION OF ENDOTHELIAL NOS AT THE BASAL MICROTUBULE MEMBRANE IN CILIATED EPITHELIUM OF RAT LUNG

Nitric oxide (NO), an important cell messenger molecule, is formed end ogenously in the lung airway, Three individual genes of NO synthase (N OS), which represent brain NOS (bNOS), inducible NOS (iNOS), and endot helial NOS (eNOS), have been reported in the cultured lung epithelium. Although studies in vivo showed that bNOS and iNOS were expressed and localized in the cytoplasm of bronchial epithelium, the expression an d localization of eNOS remains to be determined. Therefore, we employe d an eNOS monoclonal antibody whose immunospecificity was tested by bo th Western blot and preadsorption immunohistochemistry to immunostain rat lungs from fetus to adult. The results showed that eNOS immunoreac tivity began to appear in the lung epithelium within 2 hr after birth, Six hours later (8 hr after birth), the NOS immunoreaction was concen trated near the surface of the ciliated epithelial cells, This stainin g pattern appeared in lungs at Day 1, Week 1, Week 2, and in adult rat s. By electron microscopy, eNOS immunoreactivity was confirmed within ciliated epithelium and was shown to be associated with the basal micr otubule membrane of the cilia. Nonciliated cells were not stained, Typ e II epithelial cells also contain eNOS immunoreactivity, which is pri marily associated with rough endoplasmic reticulum and free ribosomes. However, macrophages in the lungs lacked eNOS immunoreactivity, This study demonstrated that eNOS was postnatally expressed in rat bronchia l ciliated epithelium. The localization of eNOS at the basal membrane of ciliary microtubules suggests that eNOS may be involved in the func tion of epithelial cilia, consistent with previous physiological studi es.