Nonselective squeeze-out of dioleoylphosphatidylcholine and dioleoylphosphatidylglycerol from binary mixed monolayers...

In order to enable the possible use of dipalmitoylphosphatidylcholine as an artificial lung surfactant, the addition of dioleoylphosphatidylcholine or dioleoylphosphatidylglycerol has been suggested. A preferential loss of molecules of the second component during compression of the interfacial layer was proposed. In this study two types of measurement were carried out in order to verify such a preferential squeeze-out. In the first type, electron micrographs of a pure dipalmitoylphosphatidylcholine monolayer and of mixed monolayers of dipalmitoylphosphatidylcholine and egg phosphatidylglycerol were taken in order to study the nature of the structures formed during compression of the monolayer. The electron microscopy photos show horizontally stacked layers in the collapse phase of dipalmitoylphosphatidylcholine, and long vertical ridges in the mixed monolayers up to 20% second component. At higher concentrations of the second component no such structures can be detected. The second type involved monolayer studies with binary mixtures of dipalmitoylphosphatidylcholine and dioleoylphosphatidylcholine or dioleoylphosphatidylglycerol, one of the pair being always radioactively labelled. Counting the radioactivities in bulk phase and monolayer after compression revealed nonselective squeeze-out of either component.