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Surfactant apoprotein Mr = 26,000-36,000 enhances uptake of liposomes by type II cells.

1987; Elsevier BV; Volume: 262; Issue: 6 Linguagem: Inglês

10.1016/s0021-9258(18)61590-x

1083-351X

Jo Rae Wright, R.E. Wager, Samuel Hawgood, Leland G. Dobbs, Judith A. Clements,

Mass Spectrometry Techniques and Applications

The alveolar type I1 cell which synthesizes and secretes surfactant also plays a major role in the reuptake of surfactant lipids.In a recent in vivo study we found that the subfractions of natural surfactant that contained the surfactant protein with molecular weights of 26,000-36,000 (SP-26-36) were preferentially taken up into lamellar bodies of type I1 cells to a greater extent than were fractions that did not contain SP-26- 36.Because the subfractions of natural surfactant in that study differed in other properties than the presence or absence of SP-26-36, the current study was undertaken to determine whether purified SP-26-36 enhanced the uptake of surfactant-like lipids by freshly isolated type I1 cells.SP-26-36 increased the uptake of label in radioactive surfactant-like lipids by up to 10-fold, and the effect of SP-26-36 was dependent on time, protein concentration, and temperature.The enhancement was inhibited by heat-treating the protein, by a polyclonal antibody against SP-26-36, and by metabolic inhibitors.The distribution of radioactivity in cell-associated phospholipids differed if cells were incubated with or without SP-26-36.If SP-26-36 was present during the incubation, greater than 96% of the radioactivity remained associated with phosphatidylcholine.In the absence of SP-26-36, only 85% of the radioactivity remained associated with phosphatidylcholine and 7% of the label appeared in phosphatidylglycerol.We hypothesize that SP-26-36 may act as a ligand to direct surfactant lipids to type I1 cells, perhaps to different metabolic pathways, and to regulate recycling and surfactant homeostasis.Lung surfactant is secreted into the air spaces by alveolar type I1 cells from organelles called lamellar bodies.The primary lipid component of surfactant is dipalmitoylphosphatidylcholine (DPPC)'; the two major protein groups have molecular weights of 26,000-36,000 (SP-26-36) and 5,000-16,000