TYPE-II EPITHELIAL-CELLS OF THE LUNG .6. INCORPORATION OF CHOLINE-H-3 AND PALMITATE-H-3 INTO LIPIDS OF CULTURED TYPE-II CELLS

  • 1 January 1980
    • journal article
    • research article
    • Vol. 42  (3) , 296-301
Abstract
Incorporation of 3H-labeled lipid precursors into surfactant-associated and non-surfactant associated phospholipids were measured in 2-7 day primary cultures of rabbit type II alveolar epithelial cells to assess the degree to which these cells retain metabolic features related to surfactant production in vitro. Unsaturated phosphatidyl choline label increased progressively in type II cell monolayers grown in the continuous presence of 3H-choline, but label in saturated phosphatidyl choline, the surfactant-associated fraction, remained constant after 2 days in culture. Although type II cell cultures could be stimulated to increase saturated phosphatidyl choline production by brief exposure to 8.5 .times. 10-5 M palmitic acid, this response was transient. Type II cells synthesized the other major surfactant-associated lipid, phosphatidyl glycerol, from 3H-palmitic acid in vitro, in proportions decreasing from 6.3% of total lipid synthesis in fresh cell isolates to 1.8% in 2 day cultures and 1.4% in 4 day cultures. Aging of the cell cultures was associated with a proportionate decrease in synthesis of neutral lipids and increases in synthesis of phosphatidyl choline, sphingomycelin and phosphatidyl inositol, from palmitic acid. Isolated type II alveolar cells continue synthesis of surfactant-related lipid species, a major index of differentiated function, for at least 4 days after introduction into cell culture. Production of non-surfactant related lipids occupies a progressively larger portion of type II cell lipid synthetic activity during this period, probably reflecting increased synthesis of cell membranes.