Influence of E. coli lipopolysaccharide binding to rat alveolar type II cells on their functional properties

The interaction between lipopolysaccharide from E. coli 0111:B4 and rat alveolar type II pneumocytes and its influence on the functional properties of the cells and their membranes were studied. Type II cells were isolated by a novel procedure involving digestion of the lung connective tissue with elastase and Percoll-gradient centrifugation. Binding of (14C)lipopolysaccharide to type II cells resulted in a partially reversible; non-specific, high affinity process. (14C)Choline incorporation into phosphatidylcholine by type II cells was stimulated by lipopolysaccharide, the maximum effect being observed at 10-20 micrograms/ml. 45Ca2+ uptake by type II cells was also increased by lipopolysaccharide. Using plasma membranes from lung homogenates an increase of membrane microviscosity versus the amount of lipopolysaccharide was shown. These results indicate that E. coli lipopolysaccharide interacts with alveolar type II cells by binding reversibly to particular ingredients of the membrane bilayer and induces a modification of ion permeability and fluidity of the membrane.