Phase separation in monolayers of pulmonary surfactant phospholipids at the air-water interface: Composition and structure

被引:92
作者
Discher, BM
Schief, WR
Vogel, V
Hall, SB
机构
[1] Oregon Hlth & Sci Univ, Dept Biochem & Mol Biol, Portland, OR 97201 USA
[2] Oregon Hlth & Sci Univ, Dept Physiol & Pharmacol, Portland, OR 97201 USA
[3] Oregon Hlth & Sci Univ, Dept Med, Portland, OR 97201 USA
[4] Univ Washington, Dept Bioengn, Seattle, WA 98195 USA
关键词
D O I
10.1016/S0006-3495(99)77046-3
中图分类号
Q6 [生物物理学];
学科分类号
071011 ;
摘要
The phase behavior of monolayers containing the complete set of purified phospholipids (PPL) obtained from calf surfactant was investigated as a model for understanding the phase transitions that precede compression of pulmonary surfactant to high surface pressure. During compression, both fluorescence microscopy and Brewster angle microscopy (BAM) distinguished domains that separated from the surrounding film. Quantitative analysis of BAM grayscales indicated optical thicknesses for the PPL domains that were similar to the liquid condensed phase for dipalmitoyl phosphatidylcholine (DPPC), the most abundant component of pulmonary surfactant, and higher and less variable with surface pressure than for the surrounding film. BAM also showed the optical anisotropy that indicates long-range orientational order of tilted lipid chains for the domains, but not for the surrounding film. Fluorescence microscopy shows that addition of DPPC to the PPL increased the area of the domains. At fixed surface pressures from 20-40 mN/m, the total area of each phase grew in proportion with the mol fraction of DPPC. This constant variation allowed analysis of the DPPC mol fraction in each phase, construction of a simple phase diagram, and calculation of the molecular area for each phase. Our results indicate that the phase surrounding the domains is more expanded and compressible, and contains reduced amounts of DPPC in addition to the other phospholipids. The domains contain a mol fraction for DPPC of at least 96%.
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页码:2051 / 2061
页数:11
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