Surfactant-associated protein inhibits phospholipid secretion from type II cells

J Appl Physiol (1985). 1987 Aug;63(2):692-8. doi: 10.1152/jappl.1987.63.2.692.


Secretion of [3H]phosphatidylcholine ([3H]PC) from isolated rat pulmonary type II epithelial cells was inhibited by the surfactant-associated protein of Mr = 35,000 (SAP-35) purified from canine lung surfactant. SAP-35 inhibited [3H]PC secretion in a dose-dependent manner and significantly inhibited basal, phorbol ester, beta-adrenergic, and P2-purinergic agonist-induced [3H]PC secretion. SAP-35 significantly inhibited [3H]PC secretion from 1 to 3 h after treatment. The IC50 for inhibition of [3H]PC secretion by canine SAP-35 was 1-5 X 10(-6) g/ml and was similar for inhibition of both basal and secretagogue-stimulated release. Heat denaturation of SAP-35, addition of monoclonal anti-SAP-35 antibody, reduction and alkylation of SAP-35, or association of SAP-35 with phospholipid vesicles reversed the inhibitory effect on secretagogue-induced secretion. Inhibitory effects of SAP-35 were observed 3 h after cells were washed with buffer that did not contain SAP-35. Although SAP-35 enhanced reassociation of surfactant phospholipid with isolated type II cells, its inhibitory effect on secretion of [3H]PC did not result from stimulation of reuptake of secreted [3H]PC by type II cells. The inhibition of phospholipid secretion by SAP-35 was also not due to inhibition of PC or disaturated PC synthesis by SAP-35. SAP-35, the major phospholipid-associated protein in pulmonary surfactant, is a potent inhibitor of surfactant secretion from type II cells in vitro and may play an important role in homeostasis of surfactant in the alveolar space.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Adenosine Triphosphate / pharmacology
  • Animals
  • Cells / classification
  • Cells, Cultured
  • Chemical Phenomena
  • Chemistry
  • Epithelial Cells
  • Epithelium / metabolism
  • Lung / cytology
  • Lung / metabolism*
  • Male
  • Phosphatidylcholines / antagonists & inhibitors
  • Phosphatidylcholines / metabolism*
  • Proteolipids / pharmacology*
  • Pulmonary Surfactant-Associated Protein A* / analogs & derivatives*
  • Pulmonary Surfactant-Associated Proteins
  • Pulmonary Surfactants / pharmacology*
  • Rats


  • Phosphatidylcholines
  • Proteolipids
  • Pulmonary Surfactant-Associated Protein A
  • Pulmonary Surfactant-Associated Proteins
  • Pulmonary Surfactants
  • SFTPA1 protein, human
  • Adenosine Triphosphate