Abstract
Lung surfactant films at the air/water interface exhibit the particularity that surfactant molecules are expelled from the surface monolayer into a surface associated multilamellar phase during compression. They are able to re-enter the surface film during the following expansion. The underlying mechanism for this behavior is not fully understood yet. However, an important role is ascribed to the surfactant-associated protein C (SP-C). Here, we studied a model lung surfactant, consisting of dipalmitoylphosphatidylcholine (DPPC), dipalmitoylphosphatidylglycerol (DPPG), and SP-C, by means of scanning near-field optical microscopy (SNOM). Attaching a fluorescent dye to the protein allowed the localization of its lateral distribution at various surface pressures with high resolution. At an early stage of compression, the film appears demixed into a pure lipid phase and a protein-enriched phase. Within the latter phase, protein aggregations are revealed. They show a uniform density, having three times the fluorescence intensity of their surroundings. Across the phase boundary between the lipid phase and the protein-rich phase, there is a protein density gradient rather than an abrupt border. When the film is highly compressed, we observe the formation of multilamellar structures that are fluorescent. They are often surrounded by a slightly fluorescent monolayer. The fluorescence of the multilayer stacks (i. e., the protein content per unit area) is proportional to the height of the stacks.
Full Text
The Full Text of this article is available as a PDF (295.9 KB).
Selected References
These references are in PubMed. This may not be the complete list of references from this article.
- Amrein M., von Nahmen A., Sieber M. A scanning force- and fluorescence light microscopy study of the structure and function of a model pulmonary surfactant. Eur Biophys J. 1997;26(5):349–357. doi: 10.1007/s002490050089. [DOI] [PubMed] [Google Scholar]
- Betzig E., Trautman J. K., Harris T. D., Weiner J. S., Kostelak R. L. Breaking the diffraction barrier: optical microscopy on a nanometric scale. Science. 1991 Mar 22;251(5000):1468–1470. doi: 10.1126/science.251.5000.1468. [DOI] [PubMed] [Google Scholar]
- Pérez-Gil J., Nag K., Taneva S., Keough K. M. Pulmonary surfactant protein SP-C causes packing rearrangements of dipalmitoylphosphatidylcholine in spread monolayers. Biophys J. 1992 Jul;63(1):197–204. doi: 10.1016/S0006-3495(92)81582-5. [DOI] [PMC free article] [PubMed] [Google Scholar]
- von Nahmen A., Post A., Galla H. J., Sieber M. The phase behavior of lipid monolayers containing pulmonary surfactant protein C studied by fluorescence light microscopy. Eur Biophys J. 1997;26(5):359–369. doi: 10.1007/s002490050090. [DOI] [PubMed] [Google Scholar]
- von Nahmen A., Schenk M., Sieber M., Amrein M. The structure of a model pulmonary surfactant as revealed by scanning force microscopy. Biophys J. 1997 Jan;72(1):463–469. doi: 10.1016/S0006-3495(97)78687-9. [DOI] [PMC free article] [PubMed] [Google Scholar]