Incorporation of biotinylated SP-A into rat lung surfactant layer, type II cells, and clara cells.
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.
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- Respiratory System
- Rats, Sprague-Dawley
- Rats
- Pulmonary Surfactants
- Pulmonary Surfactant-Associated Proteins
- Pulmonary Surfactant-Associated Protein A
- Proteolipids
- Microscopy, Electron
- Male
- Lung
Citation
Published In
DOI
ISSN
Publication Date
Volume
Issue
Start / End Page
Location
Related Subject Headings
- Respiratory System
- Rats, Sprague-Dawley
- Rats
- Pulmonary Surfactants
- Pulmonary Surfactant-Associated Proteins
- Pulmonary Surfactant-Associated Protein A
- Proteolipids
- Microscopy, Electron
- Male
- Lung