Hydrophobic lung surfactant proteins B and C remain associated with surface film during dynamic cyclic area changes

Abstract

The biophysical activity of lung surfactant depends, to a large extent, on the presence of the hydrophobic surfactant proteins B (SP-B) and C (SP-C). The role of these proteins in lipid adsorption and lipid squeeze-out under dynamic conditions simulating breathing is not yet clear. Therefore, the aim of this study was to investigate the interaction of spread hydrophobic surfactant proteins with phospholipids in a captive-bubble surfactometer during rapid cyclic area changes (6 cycles/min). We found that SP-B and SP-C facilitated the rapid transport of lipids into the air-water interface in a concentration-dependent manner (threshold concentration > or = 0.05:0.5 mol% SP-B/SP-C). Successive rapid cyclic area changes did not affect the concentration-dependent lipid adsorption process, suggesting that SP-B and SP-C remained associated with the surface film.

The Role of Surfactant Proteins in DPPC Enrichment of Surface Films

“…If an enrichment of the monolayer in DPPC occurs, only a relatively small amount of non-DPPC lipids has to be removed. In earlier studies using the CBS, we observed that refinement did indeed occur and was completed after one or two cycles (Putz et al, 1999;Veldhuizen et al, 1999). In this study, DPPC was gradually substituted by POPC until a limiting effect of this substitution in the surface activity of the sample was observed.…”

“…A clear effect of the percentage of DPPC on the ␥ min values of protein-free spread films, on a subphase containing liposomes with the same composition, was observed. In previous studies (Veldhuizen et al, 1999(Veldhuizen et al, , 2000Putz et al, 1998Putz et al, , 1999 80% DPPC was used as the standard lipid mixture, which results in near-zero minimum surface tensions during cycling. However, when lowered amounts of DPPC were present, the films caused higher minimum surface tensions, as shown in Fig.…”

Roles of γ-Globulin in the Dynamic Interfacial Behavior of Mixed Dipalmitoyl Phosphatidylcholine/γ-Globulin Monolayers at Air/Liquid Interfaces

“…Moreover, the results obtained by epifluorescence and dark-field microscopy provided evidence that SP-B and SP-C acted in softening the lipids, presumably essential for a high structural flexibility of the monolayer at higher lateral pressures, and were involved in surface refinement by means of squeeze-out of monolayer materials upon compression (22). However, during rapid cyclic area changes, it has been suggested that SP-B and SP-C remained associated with the surface film (23).…”

“…This variation is probably due to the differences in their surface properties at the interface. As a result, the dynamic surface properties of mixed phospholipid/protein monolayers relative to lung surfactant systems at the air/liquid interface have been studied by many investigators (8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22)(23).…”

Structure of SP-B/DPPC Mixed Films Studied by Neutron Reflectometry

“…There has been considerable interest in the changes induced in surfactant phospholipid films by SP-B (as well as the smaller, even more hydrophobic peptide, SP-C) at the air/water interface. The surface activity of films of phospholipids mixed with SP-B have been studied by captive bubble methods (15), which demonstrated that SP-B facilitates rapid incorporation of lipids into the air/water interface and that the protein remains associated with the surface film. Langmuir trough measurements have also been reported on phospholipid/SP-B mixtures; results demonstrated evidence that the protein was lost from saturated lipid films at high surface pressures (16).…”