DIFFERENT CONTRIBUTION OF PHOSPHOLIPID AND TRIACYLGLYCEROL METABOLISMTO ESTERIFICATION OF FREE INTRACELLULAR ARACHIDONATE - A STUDY ON SK-N-BE(2) HUMAN NEUROBLASTOMA-CELLS

When SK-N-BE(2) human neuroblastoma cells were exposed for Ih to growt h medium supplemented with [C-14]arachidonic acid (AA) at final concen trations ranging from 1 mu M to 100 mu M, an amount of this fatty acid was uptaken ranging form a 2% to a 120% of that present in cells at s teady state. As more [C-14]AA was uptaken by cells, a larger fraction was progressively incorporated into triacylglycerols (TAG) in comparis on to phospholipids (PL), with minor amounts remaining in a free form. By gas chromatografic analysis it was estimated that TAG from cells g rown in ordinary medium contained about 2 nmoles AA per mg protein, bu t, after Ih exposure to medium supplemented with 100 mu M AA (label-fr ee) this value rose to about 28 nmoles/mg protein; furthermore, as est imated on the basis of total fatty acid content, TAG mass was increase d by a 16%. Cell exposure to medium enriched with 100 mu M AA did not cause PL mass changes, whereas AA content was significantly increased only in phosphatidylcholine. Medium enrichment with 100 mu M AA dramat ically enhanced [H-3]glycerol incorporation into TAG, as assessed afte r Ih cell pulse, with minor but significant changes observed also for phosphatidylinositol and phosphatidylethanolamine, but not for phospha tidylcholine. In the light of these data, the contribution of PL and T AG to the removal of free intracellular AA is discussed.