EXPRESSION OF CYP2B1 IN FRESHLY ISOLATED AND PROLIFERATING CULTURES OF EPITHELIAL RAT LUNG-CELLS

Bronchiolar Clara cells and alveolar type 2 cells of the lung are know n to express relatively high levels of P450 enzymes compared to other pulmonary cells. Populations of enriched type 2 cells and Clara cells were isolated from rat lung by a procedure including lung perfusion, p rotease digestion, centrifugal elutriation, and differential attachmen t. Alveolar macrophages were removed by lavage. The Purity of the type 2 cell-enriched population was approximately 90%, and the purity of t he Clara cell-enriched population was 40-50%. Both type 2 cells and th e cells of the Clara cell-enriched population proliferated in culture. CYP2B1 mRNA was expressed approximately to the same level in type 2 c ells and the Clara cell-enriched population. The mRNA levels remained roughly constant for both cell types throughout the culture period, ex cept for an early transient reduction. The apoenzyme level of CYP2B1 w as 2-3 times higher in freshly belated cells of the Clara cell-enriche d population than in the type 2 cells. Both epithelial cell types show ed decreased level of CYP2B1 apoenzyme in culture. The differences in the CYP2B1 mRNA and apoenzyme expression levels in freshly isolated ce lls and cultured cells suggest the existence of a post-transcriptional regulatory mechanism for CYP2B1 expression in lung cells. The charact erization of specific functions of lung cells in culture, such as P450 gene expression, provides necessary information for the use of the ce lls in in vitro pulmonary toxicology.