Biochemical characterization of clonally isolated and continuously cultured type II cells from adult rat lung.

Clonally isolated and continuously cultured type II alveolar epithelial cells from adult rat lung (L-2) were compared to clonally cultured rat lung fibroblasts with respect to composition and biochemical function. There was no difference in phospholipid composition betweem those 2 cell types. After incubation with tritiated choline, the specific activity (cpm/nmol of lipid phosphorus) of disaturated phosphatidylcholine (PC) was lower than that of total PC in both cell types. Our findings suggest that, in our cell cultures, disaturated PC is not synthesized as a specific component of pulmonary surfactant, but more likely as a component of cell membranes. The increased DNA content of the L-2 cells indicates transformation and may be associated with the inability to synthesize surfactant. Under the described conditions, we are hesitant to use the clonally derived L-2 cell line as a model system for the study of pulmonary surfactant synthesis and secretion.