Surface Behavior of Individual Lipids Similar to Constituents of Pulmonary Surfactant

摘要

Surface films of amphipathic neutral lipids and phospholipids, similar to those found in pulmonary surfactant, were characterized by their surface behavior, including that under high surface pressure. Each lipid was studied with respect to equilibrium point, hysteresis hypercompressibility, and isotension point, the last two being newly defined parameters. It was found that saturated (straight) hydrocarbon chain molecules exhibited much lower isotension-point surface tensions than did their respective unsaturated (branched) analogs, whereas the reverse was true for the equilibrium-point surface tensions. Saturated compounds exhibited considerably more hypercompressibility than did their unsaturated analogs. The ordering of limiting surface tension at highest compression (the isotension point) was not exclusively dependent on obvious steric factors; rather, subtle and undefined electronic factors were also participating. The significantly lowest surface tensions obtained on compression were exhibited by dipalmitoyl lecithin, sphingomyelin, and palmitic acid. The last compound demonstrates that lipids other than phospholipids can exhibit surface activity similar to pulmonary surfactant. Development of post-isotension-point hysteresis was limited to the saturated class of molecules tested. (Author)