title: Incorporation of biotinylated SP-A into rat lung surfactant layer, type II cells, and clara cells.
abstract: The goal of this study was to compare the functions of Clara and type II cells during alveolar clearance and recycling of surfactant protein (SP) A, a secretory product of both cell types. We examined the incorporation of instilled biotinylated SP-A (bSP-A) into rat lung type II and Clara cells as a measure of clearance and recycling of the protein. Ultrastructural localization of bSP-A was accomplished by an electron-microscopic immunogold technique at 7, 30, and 120 min after intratracheal instillation. Localization of bSP-A was quantitatively evaluated within extracellular surfactant components (lipid-rich forms: myelin figures, vesicles, and tubular myelin; and lipid-poor hypophase) and in compartments of type II and Clara cells. bSP-A was incorporated into myelinic and vesicular forms of extracellular surfactant, but tubular myelin and hypophase had little bSP-A. Lamellar bodies of type II cells demonstrated a significant time-dependent increase in their incorporation of bSP-A. There was a concentration of bSP-A in the secretory granules and mitochondria of Clara cells, but no Clara cell compartment showed a pattern of time-dependent change in immunolabeling. Our immunolabeling data demonstrated a time-dependent movement of exogenous SP-A from extracellular components into type II cells and their secretory granules. Clara cells did not demonstrate a time-dependent incorporation of bSP-A into their secretory granules during the period of this study. If Clara cells recycle SP-A, they must reach a steady state very quickly or very slowly.
authors.affiliation: Department of Medicine, Veterans Affairs Medical Center and Duke University Medical Center, Durham, North Carolina 27705, USA. jsavov@acpub.duke.edu
authors.forename: J
authors.initials: J
authors.lastname: Savov
authors.forename: J R
authors.initials: JR
authors.lastname: Wright
authors.forename: S L
authors.initials: SL
authors.lastname: Young
mesh_terms: D000818:Animals; D001710:Biotin / Q000378:metabolism*; D005110:Extracellular Space / Q000378:metabolism; D007150:Immunohistochemistry; D008168:Lung / Q000166:cytology / Q000378:metabolism* / Q000648:ultrastructure; D008297:Male; D008854:Microscopy, Electron; D011510:Proteolipids / Q000378:metabolism*; D037662:Pulmonary Surfactant-Associated Protein A; D037661:Pulmonary Surfactant-Associated Proteins; D011663:Pulmonary Surfactants / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley
chemical_list: D011510:Proteolipids; D037662:Pulmonary Surfactant-Associated Protein A; D037661:Pulmonary Surfactant-Associated Proteins; D011663:Pulmonary Surfactants; D001710:Biotin