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1 December 2004 High-resolution Studies of Lung Surfactant Collapse
Rachel Sibug-Aga, Robert C. Dunn
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Survanta is a replacement lung surfactant (LS) used in the treatment of respiratory distress syndrome (RDS), the fourth leading cause of infant mortality in the United States. It consists of purified LS from bovine sources and retains the surfactant proteins (SP) SP-B and SP-C, both thought to be important in proper respiratory function. As such, it provides a useful and biologically relevant model system to probe the structure and function of natural LS. Here, we report results from high-resolution studies on model monolayers formed from Survanta to probe the mechanism of collapse at high surface pressure. Our results show the formation of two different collapse structures. At 62 mN/m, slightly below the collapse pressure, monolayer collapse occurs through buckling. Confocal fluorescence measurements on supported films reveal regions of overlapping phase structure in the films that mark the transition from monolayer to multilayer. Simultaneous near-field scanning optical microscopy fluorescence and force measurements show that the transition seen in the fluorescence measurements accompanies corresponding ∼4–5 nm changes in membrane topography. This change in height is consistent with bilayer formation on monolayer collapse. Analysis of the phase structure near the transitions also suggests that the buckling occurs from a continuous film. However, when the film is compressed to its collapse pressure of 65 mN/m, buckling is no longer evident in the collapsed region. In addition, multilayers and lipid–protein aggregates that are up to 40 nm higher than the monolayer are observed in the collapsed film at this pressure.

Rachel Sibug-Aga and Robert C. Dunn "High-resolution Studies of Lung Surfactant Collapse," Photochemistry and Photobiology 80(3), 471-476, (1 December 2004).<0471:HSOLSC>2.0.CO;2
Received: 2 August 2004; Accepted: 1 September 2004; Published: 1 December 2004

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