DIACYLGLYCEROL AND PHOSPHATIDATE GENERATED BY PHOSPHOLIPASE-C AND PHOSPHOLIPASE-D, RESPECTIVELY, HAVE DISTINCT FATTY-ACID COMPOSITIONS AND FUNCTIONS - PHOSPHOLIPASE D-DERIVED DIACYLGLYCEROL DOES NOT ACTIVATE PROTEIN-KINASE-C IN PORCINE AORTIC ENDOTHELIAL-CELLS

Stimulation of cells with certain agonists often activates both phosph olipases C and D. These generate diacylglycerol and phosphatidate, res pectively, although the two lipids are also apparently interconvertabl e through the actions of phosphatidate phosphohydrolase and diacylglyc erol kinase. Diacylglycerol activates protein kinase C while one role for phosphatidate is the activation of actin stress fiber formation, T herefore, if the two lipids are interconvertable, it is theoretically possible that an uncontrolled signaling loop could arise. To address t his issue structural analysis of diacylglycerol, phosphatidate, and ph osphatidylbutanol (formed in the presence of butan-1-ol) from both Swi ss 3T3 and porcine aortic endothelial cells was performed. This demons trated that phospholipase C activation generates primarily polyunsatur ated species while phospholipase D activation generates saturated/mono unsaturated species. in the endothelial cells, where phospholipase D w as activated by lysophosphatidic acid independently of phospholipase C , there was no activation of protein kinase C. Thus we propose that on ly poly-unsaturated diacylglycerols and saturated/monounsaturated phos phatidates function as intracellular messengers and that their interco nversion products are inactive.