Binding and uptake of surfactant protein B by alveolar type II cells

Surfactant protein B (SP-B, mol wt 9,000, reduced) is a low-molecular-weight hydrophobic protein found in organic extracts of lung surfactant. The interaction of iodinated bovine SP-B (125I-SP-B) and isolated rat alveolar type II cells was examined. The association of SP-B with the lung cells was ti...

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Bibliographic Details
Published inThe American journal of physiology Vol. 263; no. 3 Pt 1; p. L333
Main Authors Bates, S R, Beers, M F, Fisher, A B
Format Journal Article
LanguageEnglish
Published United States 01.09.1992
Subjects
Animals
Binding, Competitive
Cells, Cultured
Phospholipids - metabolism
Phospholipids - pharmacology
Proteolipids - metabolism
Pulmonary Alveoli - cytology
Pulmonary Alveoli - metabolism
Pulmonary Surfactants - metabolism
Pulmonary Surfactants - pharmacology
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Summary:Surfactant protein B (SP-B, mol wt 9,000, reduced) is a low-molecular-weight hydrophobic protein found in organic extracts of lung surfactant. The interaction of iodinated bovine SP-B (125I-SP-B) and isolated rat alveolar type II cells was examined. The association of SP-B with the lung cells was time and temperature dependent; type II cells exhibited time-dependent binding (at 4 degrees C) and uptake (at 37 degrees C) of SP-B. Binding of phospholipid-poor 125I-SP-B was linearly related to the external SP-B concentration from 0.25 to 60 microgram/ml and was not inhibited by a 60-fold excess of unlabeled SP-B. However, the binding of 125I-SP-B reconstituted with bovine surfactant or with phospholipid-containing liposomes occurred through a high-affinity, saturable process and could be inhibited with unlabeled SP-B. By Scatchard analysis, half-maximum binding in the presence of surfactant occurred at 3.1 +/- 0.7 micrograms SP-B/ml. Saturable binding of SP-B reconstituted with surfactant also occurred with other cell types. The results indicate that SP-B was bound and internalized by type II cells. The apparent lack of specificity in the absence of phospholipid may have been due to the self-association of SP-B. The reconstitution of SP-B with phospholipid altered the binding of phospholipid-poor SP-B from a nonspecific process to a high-affinity process consistent with a cell surface binding site.
ISSN:0002-9513
2163-5773
DOI:10.1152/ajplung.1992.263.3.l333