Influence of lipid saturation grade and head group charge: A refined lung surfactant adsorption model
Ute Klenz 1, Mohammed Saleem 1, Michaela C Meyer 1 and Hans-Joachim Galla 2*
1 Institute of Biochemistry, University of Muenster,Germany
2 Institue of Biochemistry, University of Muenster,Germany
* To whom correspondence should be addressed. E-mail: gallah{at}uni-muenster.de.
Submitted on February 7, 2008
Revised on February 13, 2008
Accepted on 20 March 2008
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Abstract |
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Rapid adsorption of surfactant material to the air/liquid interface of the lung is essential for maintaining normal lung function. The detailed mechanism of this process, however, still remains unclear. In this study we therefore wanted to elucidate the influence of lipid saturation grade and head group charge of surface layer lipids on surfactant protein-induced vesicle insertion into monolayers spread at the air/water interface of a film balance. We used DPPC, DPPG, POPC and POPG as monolayer lipids doped with either surfactant protein B or C (0.2 and 0.4 mol%, respectively). Vesicles consisting of DPPC/DPPG (4:1, mol ratio) were injected into a stirred subphase in order to quantify adsorption kinetics. Based on kinetic film balance and fluorescence measurements a refined model describing distinct steps of vesicle adsorption to surfactant monolayers is presented. First, in a protein-independent step, lipids from vesicles bridged to the interfacial film by Ca2+-ions are inserted into defects of a disordered monolayer at low surface pressures. Second, in a surfactant-protein facilitated step, active material insertion involving a SP-B or SP-C induced flip-flop of lipids occurs at higher surface pressures. Negatively charged lipids obviously influence the threshold pressures at which this second protein-mediated adsorption mechanism takes place.
Key Words:
Film balance, Fluorescence Microscopy, Kinetic study, SP-B, SP-C, Vesicle insertion
