Mechanisms involved in the synthesis of disaturated phosphatidylcholine by alveolar type II cells isolated from adult rat lung.

1. Alveolar type II cells isolated from adult rat lung incorporated radioactively labelled palmitate predominantly into the 2-position of disaturated phosphatidylcholine. In disaturated diacylglycerol, however, the radioactivity was almost equally distributed between the 1- and 2-positions. 2. Exposure of isolated type II cells to the phospholipase A2 inhibitors 4-bromophenacylbromide or quinacrine dihydrochloride led to a decreased synthesis of total phosphatidylcholines from various labelled precursors. Interestingly, it also led to an increased degree of unsaturation of the phosphatidylcholines synthesized by the cells. 3. Incubation of type II cell sonicates with radioactively labelled CDPcholine resulted in the formation of labelled phosphatidylcholine; 56% of this phosphatidylcholine appeared to be disaturated. In similar experiments with homogenates from whole lung, 20% of the synthesized phosphatidylcholine was disaturated. 4. These results suggest that both direct synthesis de novo and remodeling of 1-saturated-2-unsaturated phosphatidylcholines contribute to the biosynthesis of disaturated phosphatidylcholine in isolated alveolar type II cells.