Yu S H, Possmayer F
Department of Obstetrics and Gynecology, The University of Western Ontario, London, Canada.
J Lipid Res. 1998 Mar;39(3):555-68.
Interaction of pulmonary surfactant protein A (SP-A) with pure and binary mixed dipalmitoylphosphatidylcholine (DPPC) and cholesterol (3.5 wt%) at the air/saline, 1.5 mM CaCl2 interface was investigated using a rhomboid surface balance at 37 degrees C. Surface tension-area isotherms were measured to access the surface active properties of the monolayers. The organization of DPPC and cholesterol in DPPC and DPPC/cholesterol mixed monolayers with or without SP-A at equilibrium surface tension (approximately 23 mN/N) was revealed by autoradiographs of Langmuir-Blodgett (L-B) films deposited from [14C]DPPC or [14C]cholesterol-labeled monolayers. The results showed that SP-A can interact with the polar head groups of DPPC monolayers and aggregate DPPC molecules. SP-A decreased the surface area reduction required for DPPC monolayers to achieve near zero surface tension from 30 to 25% of the area at equilibrium. SP-A also reduced the collapse surface tension of pure cholesterol from 27 to 23 mN/m. DPPC and cholesterol formed homogeneous mixed monolayers when both were dissolved in the spreading solvent prior to spreading, while separate cholesterol-rich domains appeared when DPPC and cholesterol were spread successively. Cholesterol resisted squeeze-out from either mixed monolayer through compression. Although SP-A could not promote the squeeze-out of cholesterol from homogeneous mixed monolayers, it facilitated that of cholesterol domains especially when SP-A had first interacted with DPPC. These results indicate that pulmonary surfactant protein A facilitates the squeeze-out of cholesterol domains from mixed monolayers by condensing DPPC and limiting lateral interactions of DPPC with cholesterol domains.
在37℃下，使用菱形表面天平研究了肺表面活性物质蛋白A（SP-A）与纯的及二元混合的二棕榈酰磷脂酰胆碱（DPPC）和胆固醇（3.5 wt%）在空气/盐水、1.5 mM氯化钙界面的相互作用。测量表面张力-面积等温线以了解单层的表面活性特性。通过从[14C]DPPC或[14C]胆固醇标记的单层沉积的朗缪尔-布洛杰特（L-B）膜的放射自显影片，揭示了在平衡表面张力（约23 mN/N）下，有或没有SP-A的DPPC和DPPC/胆固醇混合单层中DPPC和胆固醇的组织情况。结果表明，SP-A可与DPPC单层的极性头部基团相互作用并聚集DPPC分子。SP-A将DPPC单层达到接近零表面张力所需的表面积减少量从平衡时面积的30%降低至25%。SP-A还将纯胆固醇的崩溃表面张力从27 mN/m降低至23 mN/m。当DPPC和胆固醇在铺展前都溶解在铺展溶剂中时，它们形成均匀的混合单层，而当DPPC和胆固醇相继铺展时，会出现单独的富含胆固醇的区域。胆固醇在压缩时抵抗从任何一种混合单层中被挤出。虽然SP-A不能促进胆固醇从均匀混合单层中被挤出，但它促进了胆固醇区域的挤出，尤其是当SP-A首先与DPPC相互作用时。这些结果表明，肺表面活性物质蛋白A通过凝聚DPPC并限制DPPC与胆固醇区域的横向相互作用，促进了胆固醇区域从混合单层中被挤出。
