ROLE OF CALCIUM IONOPHORE AND PHOSPHOLIPASE A(2) - INHIBITORS ON THE FATTY-ACID COMPOSITION OF HEPATOMA TISSUE-CULTURE CELLS AND LIPID SECRETION

The effect of ionophore A-23187 (10 mu M) on the fatty acid compositio n of polar and neutral lipids was studied in hepatoma tissue culture c ells. As a consequence of a rise in calcium concentration, the monouns aturated fatty acids palmitoleic and oleic increased, whereas polyunsa turated fatty acids from the n-6 and n-3 series declined in cellular p hospholipids after 10 min incubation. The ionophore also produced a de crease in the relative content of oleic acid in neutral lipids. In the secreted lipids, there was a significant rise in the percentage of ar achidonic and eicosapentaenoic acids in the phospholipid fraction toge ther with a decrease in oleic acid, caused by the incubation of cells with the ionophore. A different effect was apparent in the fatty acid composition of the secreted neutral lipids, with a decline in the rela tive content of palmitic and stearic acids and a simultaneous increase in oleic acid. All these effects were completely suppressed by pre-tr eatment of the cells with the phospholiphase A(2) inhibitors quinacrin e dihydrocloride (0.15 mM) and 4-bromophenacyl-bromide (0.05 mM). We c onclude that phospholipase A(2) is involved in the calcium-mediated ch anges in cell fatty acid composition and secretion.