Pinto R A, Hawgood S, Clements J A, Benson B J, Naidu A, Hamilton R L, Wright J R
Cardiovascular Research Institute, University of California, San Francisco 94143-0130.
Biochim Biophys Acta. 1995 Mar 2;1255(1):16-22. doi: 10.1016/0005-2760(94)00205-d.
Surfactant protein C (SP-C) is a small hydrophobic protein that is synthesized and secreted by alveolar type II cells. The mechanism of clearance of SP-C from the alveolar airspace is not well understood, although previous studies demonstrated that recombinant SP-C instilled into the lungs of spontaneously breathing anaesthetized rats was taken up by type II cells and incorporated into lamellar bodies. The current investigation was undertaken to characterize the interaction of a complex of SP-C and surfactant-like lipids with freshly isolated rat alveolar type II cells under conditions in which the extracellular milieu can be regulated. SP-C was isolated from alveolar proteinosis lavage fluid and radiolabeled with 125I-Bolton-Hunter reagent. The radiolabeled protein retained its ability to facilitate adsorption of phospholipids to an air/liquid interface. Labeled human SP-C associated with isolated type II cells in a concentration-dependent manner that was also dependent upon temperature and time. The association of labeled SP-C with isolated type II cells did not saturate up to 150 micrograms/ml. SP-A significantly enhanced the association of SP-C with isolated type II cells. Under the experimental conditions tested, SP-C was not degraded to TCA-soluble products. These results are consistent with the hypothesis that association or uptake of SP-C by type II cells may be enhanced by SP-A and that like SP-A, SP-C is recycled by type II cells.
表面活性蛋白C（SP-C）是一种由II型肺泡细胞合成并分泌的小疏水蛋白。尽管先前的研究表明，将重组SP-C注入自主呼吸的麻醉大鼠肺中后，会被II型细胞摄取并整合到板层小体中，但SP-C从肺泡气腔清除的机制仍未完全清楚。目前的研究旨在表征在可调节细胞外环境的条件下，SP-C与表面活性剂样脂质复合物与新鲜分离的大鼠II型肺泡细胞之间的相互作用。从肺泡蛋白沉积症灌洗液中分离出SP-C，并用125I-博尔顿-亨特试剂进行放射性标记。放射性标记的蛋白质保留了促进磷脂吸附到气/液界面的能力。标记的人SP-C以浓度依赖性方式与分离的II型细胞结合，这种结合也取决于温度和时间。在高达150微克/毫升的浓度下，标记的SP-C与分离的II型细胞的结合并未达到饱和。SP-A显著增强了SP-C与分离的II型细胞的结合。在所测试的实验条件下，SP-C未降解为三氯乙酸可溶性产物。这些结果与以下假设一致，即SP-A可能增强II型细胞对SP-C的结合或摄取，并且与SP-A一样，SP-C可被II型细胞循环利用。
