Recycling of surfactant lipid and apoprotein-A studied by electron microscopic autoradiography.

Published

Journal Article

Recycling of lipid and apoprotein components by lung epithelium appears to be a key part of the metabolism of surfactant, but many details of this process are poorly understood, including its efficiency and which intracellular pathways participate. We chose electron microscopic autoradiography to track time-dependent changes in the intracellular location of [methyl-3H]-choline dipalmitoyl phosphatidylcholine or 125I-labeled apoprotein-A that were incorporated into liposomes and instilled intratracheally into rats or added to cultures of freshly isolated rat lung type II cells. At times from 2 to 120 min after the start of labeling, lungs or cells were fixed and processed for autoradiography. We found a time-dependent uptake of lipid and apoprotein by type II cells and by macrophages but not by other lung cell types. There was a time-dependent incorporation of lipid and apoprotein label into lamellar bodies, but the labels appeared in other intracellular compartments without a convincing time-dependent relationship to lamellar bodies. Although all type II cell organelles received some lipid-bound label, the apoprotein-bound label was not found within electron-dense multivesicular bodies (d-MVB). Selective lack of apoprotein label in d-MVB indicated a segregation of lipid and apoprotein labels and suggested a unique role for the d-MVB, possibly as a degradation pathway. Our results also provided conclusive morphological evidence of surfactant lipid and apoprotein recycling by type II cells.

Full Text

Cited Authors

  • Young, SL; Fram, EK; Larson, E; Wright, JR

Published Date

  • July 1993

Published In

Volume / Issue

  • 265 / 1 Pt 1

Start / End Page

  • L19 - L26

PubMed ID

  • 8338178

Pubmed Central ID

  • 8338178

Electronic International Standard Serial Number (EISSN)

  • 2163-5773

International Standard Serial Number (ISSN)

  • 0002-9513

Digital Object Identifier (DOI)

  • 10.1152/ajplung.1993.265.1.l19

Language

  • eng