Pulmonary surfactant, the major secretion of the alveolar epithelium, has been isolated in purified form from non-human animals and its chemical nature and cellular source have been characterized. These studies have generated the concepts (1) that type II epithelial cells synthesize and secrete surfactant, (2) that beta-adrenergic agonists and agents which increase cellular cAMP elicit release of surfactant, and (3) that surfactant is a lipid-protein complex in which proteins may play important informational roles. In contrast, there is little information on human surfactant. The regulation of synthesis and secretion of surfactant from human type II cells, the presumed cellular source, or details of the chemical composition of human surfactant have been examined only superficially. The goals of our proposed studies are to define the composition of human surfactant and to characterize secretions, and the agents which elicit secretion, from human type II cells. We will determine the phospholipid composition of human surfactant purified from lavages obtained by bronchoscopy and from cadaver lungs. The protein constituents will be studied in detail. We will carry out studies to determine the molecular sizes, number of isoforms, amino acid composition, and N-terminal sequence of human surfactant apoproteins. We will test purified human surfactant apoproteins for their ability to enhance the rate of adsorption of surfactant lipids to an air-liquid interface. We will develop methods for the isolation of type II cells from segments of human lung obtained at surgery. Using a satisfactory type II cell preparation, we will characterize the cells and their secretions by biochemical and morphologic methods. We will identify agents which stimulate secretion of surfactant by a direct effect on type II cells, and we will characterize in detail the cellular effects of positive agonists. We will characterize the protein and phospholipid composition of the secretions using electrophoresis, chromatography, and immunoblot methods which are standard in our laboratory. We will also determine whether human type II cells secrete certain lysosomal enzymes as do rat type II cells. Changes in glycoconjugates of cellular plasma membranes as a function of time in culture will be assessed by lectin-binding studies. These studies will provide important information which will form a basis for future studies on potential alterations of human surfactant metabolism in pathologic conditions.
|Wirtz, H R; Dobbs, L G (1990) Calcium mobilization and exocytosis after one mechanical stretch of lung epithelial cells. Science 250:1266-9|