Accumulation of (n-9)-eicosatrienoic acid in confluent 3T3-L1 and 3T3 cells.

The 3T3-L1 preadipocyte cultured cell line accumulates the n-9 class of eicosatrienoic acid (20:3 n-9) after becoming confluent when the medium contains 10% fetal bovine serum. Accumulation of 20:3 n-9 also occurred in confluent, nondifferentiating 3T3 cells but not in eight other cultured cell lines that were tested. Radioisotope experiments indicate that confluent 3T3-L1 cells synthesized 20:3 n-9 from [1-14C]oleic acid. 20:3 n-9 comprised 9.8% of the cell phospholipid fatty acids, and its accumulation was associated with a 40% reduction in the phospholipid arachidonic acid content. The highest percentage of 20:3 n-9 was present in the ethanolamine and inositol glycerophospholipid fractions. Eicosatrienoic acid also accumulated in 3T3-L1 cells that were treated with dexamethasone, methylisobutylxanthine, and insulin to achieve adipocyte morphology. Supplementation of the culture medium with 0.03 mumol/ml of either linoleic or arachidonic acid prevented 20:3 n-9 accumulation. Partial reversal of the 20:3 n-9 accumulation occurred when confluent cells were either replated at a low density to initiate logarithmic growth or supplemented with 0.03 mumol/ml of arachidonic acid. The accumulation of 20:3 n-9, a polyunsaturate that ordinarily is found only in essential fatty acid deficiency, may be an important variable in studies involving 3T3-L1 and 3T3 cells.