DIACYLGLYCEROLS DERIVED FROM MEMBRANE PHOSPHOLIPIDS ARE METABOLIZED BY LIPASES IN A10 SMOOTH-MUSCLE CELLS

The metabolic fate of endogenous diacylglycerol (DAG) in cultured A10 Smooth muscle cells was determined. Preincubation of A10 cells with [H -3] myristic acid or [H-3] arachidonic acid resulted in preferential l abeling of phosphatidylcholine (PC) or phosphatidylinositol (PI), resp ectively. Addition of PC-specific phospholipase C (PC-PLC) to [H-3] my ristate-labeled A10 cells resulted in a 10-fold increase in radiolabel ed DAG, which was converted to monoacylglycerol (MG) and fatty acid (F A). DAG degradation and MG formation was inhibited by tetrahydrolipsta tin, a DAG; lipase inhibitor. PC-derived DAG was not converted to phos phatidic acid; in addition, PC resynthesis or triacylglycerol synthesi s was not observed. Addition of PI-specific PLC (PI-PLC) to [H-3] arac hidonate-labeled A10 cells resulted in a modest increase in radiolabel ed DAG that was also hydrolyzed to MG and FA. Therefore, the principal metabolic fate of endogenous DAG generated from membrane phospholipid s by treatment of A10 cells with PC-PLC and PI-PLC was hydrolysis by a DAG lipase pathway.