title: Interaction of phospholipid liposomes with plasma membrane isolated from alveolar type II cells: effect of pulmonary surfactant protein A.
abstract: Pulmonary surfactant protein A (SP-A) augments the uptake of phospholipid liposomes containing dipalmitoylphosphatidylcholine (DPPC) by alveolar type II cells. The SP-A-mediated uptake process of lipids by type II cells have not been well understood. In the present study we investigated the SP-A-mediated interaction of phospholipids with plasma membrane isolated from alveolar type II cells. SP-A increased the amount of liposomes containing radiolabeled DPPC associated with type II cell plasma membrane by 4-fold compared to the control without SP-A when analyzed by sucrose density gradient centrifugation. This effect is dependent upon the SP-A concentration. The enhancement was inhibited by anti-SP-A antibody and EGTA. When type II cell plasma membrane and liposomes containing [14C]DPPC and [3H]triolein were coincubated with or without SP-A, analysis on sucrose density gradients revealed that the profiles of [14C]DPPC and [3H]triolein in each fraction were almost identical with or without SP-A, indicating that SP-A mediates the binding of liposomes to plasma membrane but not transfer of DPPC. SP-A increased the association of liposomes containing DPPC with the membrane by 2-fold more than that containing 1-palmitoyl-2-linoleoyl-phosphatidylcholine (PLPC). SP-A induced aggregation of phospholipid liposomes containing PLPC as well as those containing DPPC, but the final turbidity of DPPC liposomes aggregated by SP-A was only by 15% greater than that of PLPC liposomes. The amount of DPPC liposomes associated with the plasma membrane derived from type II cells was 2-fold greater than that from liver. We speculate that the SP-A-mediated interaction of lipids with type II cell plasma membrane may contribute, in part, to the lipid uptake process by type II cells.
authors.affiliation: Department of Biochemistry, Sapporo Medical University School of Medicine, Japan.
authors.forename: Y
authors.initials: Y
authors.lastname: Kuroki
authors.forename: M
authors.initials: M
authors.lastname: Shiratori
authors.forename: Y
authors.initials: Y
authors.lastname: Ogasawara
authors.forename: A
authors.initials: A
authors.lastname: Hattori
authors.forename: W
authors.initials: W
authors.lastname: Tsunezawa
authors.forename: T
authors.initials: T
authors.lastname: Honma
authors.forename: T
authors.initials: T
authors.lastname: Akino
mesh_terms: D015060:1,2-Dipalmitoylphosphatidylcholine / Q000378:metabolism; D000818:Animals; D002462:Cell Membrane / Q000378:metabolism*; D008081:Liposomes / Q000378:metabolism*; D008099:Liver / Q000378:metabolism / Q000648:ultrastructure; D008297:Male; D010743:Phospholipids / Q000378:metabolism*; D011510:Proteolipids / Q000494:pharmacology*; D011650:Pulmonary Alveoli / Q000378:metabolism* / Q000648:ultrastructure; D037662:Pulmonary Surfactant-Associated Protein A; D037661:Pulmonary Surfactant-Associated Proteins; D011663:Pulmonary Surfactants / Q000494:pharmacology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D014304:Triolein / Q000378:metabolism; D014316:Tritium
chemical_list: D008081:Liposomes; D010743:Phospholipids; D011510:Proteolipids; D037662:Pulmonary Surfactant-Associated Protein A; D037661:Pulmonary Surfactant-Associated Proteins; D011663:Pulmonary Surfactants; D014316:Tritium; D014304:Triolein; D015060:1,2-Dipalmitoylphosphatidylcholine