Dipalmitoylphosphatidylcholine and cholesterol in monolayers spread from adsorbed films of pulmonary surfactant.
Pulmonary surfactant forms a surface film that consists of a monolayer and a monolayer-associated reservoir. The extent to which surfactant components including the main component, dipalmitoylphosphatidylcholine (DPPC), are adsorbed into the monolayer, and how surfactant protein SP-A affects their adsorptions, is not clear. Transport of cholesterol to the surface region from dispersions of bovine lipid extract surfactant [BLES(chol)] with or without SP-A at 37 degrees C was studied by measuring surface radioactivities of [4-(14)C]cholesterol-labeled BLES(chol), and the Wilhelmy plate technique was used to monitor adsorption of monolayers. Results showed that transport of cholesterol was lipid concentration dependent. SP-A accelerated lipid adsorption but suppressed the final level of cholesterol in the surface. Surfactant adsorbed from a dispersion with or without SP-A was transferred via a wet filter paper to a clean surface, where the surface radioactivity and surface tension were recorded simultaneously. It was observed that 1) surface radioactivity was constant over a range of dispersion concentrations; 2) cholesterol and DPPC were transferred simultaneously; and 3) SP-A limited transfer of cholesterol. These results indicate that non-DPPC components of pulmonary surfactant can be adsorbed into the monolayer. Studies in the transfer of [1-(14)C]DPPC-labeled BLES(chol) to an equal or larger clean surface area revealed that SP-A did not increase selective adsorption of DPPC into the monolayer. Evaluation of transferred surfactant with a surface balance indicated that it equilibrated as a monolayer. Furthermore, examination of transferred surfactants from dispersions with and without prespread BLES(chol) monolayers revealed a functional contiguous association between adsorbed monolayers and reservoirs.
Yu
S H
SH
Department of Obstetrics and Gynaecology, University of Western Ontario, London, Ontario, Canada N6A 5B8. shyu@uwo.ca
Possmayer
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D015060:1,2-Dipalmitoylphosphatidylcholine / Q000032:analysis / Q000737:chemistry*; D000327:Adsorption; D000818:Animals; D001345:Autoradiography; D002417:Cattle; D055598:Chemical Phenomena; D002627:Chemistry, Physical; D002784:Cholesterol / Q000032:analysis / Q000737:chemistry*; D007700:Kinetics; D011510:Proteolipids / Q000737:chemistry / Q000494:pharmacology; D037662:Pulmonary Surfactant-Associated Protein A; D037661:Pulmonary Surfactant-Associated Proteins; D011663:Pulmonary Surfactants / Q000737:chemistry* / Q000494:pharmacology; D013499:Surface Properties
D011510:Proteolipids; D037662:Pulmonary Surfactant-Associated Protein A; D037661:Pulmonary Surfactant-Associated Proteins; D011663:Pulmonary Surfactants; D015060:1,2-Dipalmitoylphosphatidylcholine; D002784:Cholesterol