Models of pulmonary surfactant: monolayers of dipalmitoylphosphatidylcholine and phosphatidylinositol

Abstract The properties of monolayers composed of dipalmitoylphosphatidylcholine (DPPC) and phosphatidylinositol (PI) from three sources have been investigated at 37°C. The monolayers were formed over subphases containing buffered physiological saline at two surface loads, and they were compressed and expanded at 3.6 cm 2 /s for five successive cycles. The minimum surface tension reached by the monolayers before their collapse was dependent on the proportions of DPPC and PI present. DPPC-rich monolayers reached very low surface tension (high surface pressure) near 0 mM m −1 while those containing only unsaturated PI collapsed between 12 and 16 mN m −1 . For any given ratio of DPPC and PI in the monolayer, when the surface load was high, the minimum surface tension was influenced slightly by the fatty acid composition of the PI, with monolayers having PI containing fewer double bonds per chain reaching slightly lower values than those containing more unsaturated chains. It was observed that neither of the three PI substantially enhanced the ability of collapsed phases to readsorb into a monolayer at the air-water interface. In this respect the PI-containing films were similar to films containing the same amounts of DPPC and an unsaturated phosphatidylglycerol that had been studied under equivalent conditions.(Biochim. Biophys. Acta (1983) 732,243–250).