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

Abstract Changes in the surface structure of Clara cells in the terminal bronchioles following exposure of rats to 0.4 ppm ozone (O 3 ) for 14 days were evaluated and compared to the content of pulmonary cytochrome P -450, an enzyme active in xenobiotic metabolism. Exposure to O 3 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 O 3 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 O 3 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.