Effect of Unsaturated Fatty Acids and Ca2+ on Phosphatidylinositol Synthesis and Breakdown

Abstract

CDP-diglyceride : inositol transferase was inhibited by unsaturated fatty acids. The inhibitory activity decreased in the following order: arachidonic acid≫linolenic acid≫linoleic acid≫oleic acid≥palmitoleic acid. Saturated fatty acids such as myristic acid, palmitic acid, and stearic acid had no effect. Calcium ion also inhibited the activity of CDP-diglyceride: inositol transferase. In rat hepatocytes, arachidonic acid inhibited ³² P incorporation into phosphatidylinositol and phosphatidic acid without any significant effect on ³² P incorporation into phosphatidylcholine, phosphatidylethanolamine and phosphatidylserine. Ca ²⁺ ionophore A23187 also inhibited ³² P incorporation into phosphatidylinositol. However, ³² P incorporation into phosphatidic acid was stimulated with Ca ²⁺ ionophore A23187. Phosphatidylinositol-specific phospholipase C was activated by unsaturated fatty acids. Polyunsaturated fatty acids such as arachidonic acid and linolenic acid had a stronger effect than di- and monounsaturated fatty acids. Saturated fatty acids had no effect on the phospholipase C activity. The phospholipase C required Ca ²⁺ for activity. Arachidonic acid and Ca ²⁺ had synergistic effects. These results suggest the reciprocal regulation of phosphatidylinositol synthesis and breakdown by unsaturated fatty acids and Ca ²⁺ .