Alteration in surface structure of Clara cells and pulmonary cytochrome P-450b level in rats exposed to ozone.

Changes in the surface structure of Clara cells in the terminal bronchioles following exposure of rats to 0.4 ppm ozone (O3) for 14 days were evaluated and compared to the content of pulmonary cytochrome P-450, an enzyme active in xenobiotic metabolism. Exposure to O3 caused a striking alteration of Clara cells in the terminal bronchiole. After 6 h exposure apical protrusions of Clara cells enlarged and these Clara cells formed clusters. However after 24 h exposure, the Clara cells decreased in number and flattened. They increased in number and enlarged again during the subsequent period of exposure. By the 14th day of O3 exposure the number of Clara cells had increased significantly. The content of cytochrome P-450b (IIB1), a main isozyme of pulmonary cytochromes P-450 of rats, was determined by an immuno-blotting method using anti-cytochrome P-450b antibody. The cytochrome P-450b in the rats exposed to O3 increased significantly to 1.37- and 1.81-times that of the control on the 7th and 14th days, respectively. Immuno-electron microscopy demonstrated that cytochrome P-450b was localized abundantly in endoplasmic reticulum of Clara cells. Morphological alterations in Clara cells appear to be closely related with changes in the cytochrome P-450b content of the lung.