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Original Article |
Correspondence to: Shou-Hwa Yu, at the Department of Obstetrics and Gynaecology, University of Western Ontario, 339 Windermere Road, London, Ontario, Canada N6A 5A5., shyu{at}uwo.ca (E-mail)
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°C was studied by measuring surface radioactivities of [4-14C]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 [1-14C]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., and F. Possmayer. Dipalmitoylphosphatidylcholine and cholesterol in monolayers spread from adsorbed films of pulmonary surfactant. J. Lipid Res. 2001. 42: 1421;1429.
Supplementary key words: air/water interface, cholesterol, DPPC, L-B film, SP-A
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