Influence of Lipid Saturation Grade and Headgroup Charge: A Refined Lung Surfactant Adsorption Model

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, remains unclear. In this study, we elucidate the influence of lipid saturation grade and headgroup charge of surface lay...

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Bibliographic Details
Published in:Biophysical journal 2008-07, Vol.95 (2), p.699-709
Main Authors: Klenz, U., Saleem, M., Meyer, M.C., Galla, H.-J.
Format: Article
Language:English
Subjects:
Adsorption
Biomimetic Materials - chemistry
Lipids
Liposomes - chemistry
Lungs
Mathematical models
Membranes
Models, Biological
Monolayers
Phospholipids - chemistry
Proteins
Pulmonary Surfactants - chemistry
Static Electricity
Surface chemistry
Surfactants
Vesicles
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Summary: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, remains unclear. In this study, we elucidate the influence of lipid saturation grade and headgroup charge of surface layer lipids on surfactant protein (SP)-induced vesicle insertion into monolayers spread at the air/water interface of a film balance. We used dipalmitoylphosphatidlycholine (DPPC),1,2-dipalmitoyl- sn-glycero-3-phosphoglycerol (DPPG), 1-palmitoyl-2-oleoyl- sn-glycero-3-phosphocholine (POPC), and 1-palmitoyl-2-oleoyl- sn-glycero-3-phosphoglycerol (POPG) as monolayer lipids doped with either hydrophobic surfactant-specific protein SP-B or SP-C (0.2 and 0.4 mol %, respectively). Vesicles consisting of DPPC/DPPG (4:1, mol ratio) were injected into a stirred subphase 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 Ca 2+ ions are inserted into defects of a disordered monolayer at low surface pressures. Second, in a SP-facilitated step, active material insertion involving an 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.
ISSN:0006-3495
1542-0086
DOI:10.1529/biophysj.108.131102