DIACYLGLYCEROL MOLECULAR-SPECIES IN PLASMA-MEMBRANE AND MICROSOMES CHANGE TRANSIENTLY WITH ENDOTHELIN-1 TREATMENT OF GLIOMA-CELLS

Agonist-induced intracellular signal transduction often involves activ ation of protein kinase C by diacylglycerol (DAG) released from membra ne phospholipids by phospholipases. Using either DAG kinase or HPLC as says to quantitatively determine DAG mass, we observed a time-dependen t increase in DAG accumulation upon incubation of rat Cb glioma cells with 200 nM endothelin-1 (ET-1). Total cell DAG rapidly increased by 2 5-35% from a basal level of 4.5 +/- 0.3 nmol/mg protein during one min of ET-1 treatment and remained constant or slightly decreased between 1 and 2 min. Thereafter, DAG increased to a maximum (1.6-fold above b asal) by 5-20 min. and remained elevated to 30 min. Resolution of DAG molecular species by HPLC after incubation of cells with ET-1 revealed that accumulation of DAG species differed in total cell lysate and su bcellular compartments. in plasma membrane, major DAG species increase d at 1 min, followed by a decrease at 10 min, whereas in microsomes DA G species did not change st 1 min. and decreased at 10 min. Although p hospholipid sources of DAG species were not identified specifically, t here was preferential hydrolysis of molecular species of phospholipid for DAG production. We propose that molecular species of DAG produced at the plasma membrane may be transferred to the endoplasmic reticulum so that phospholipid resynthesis can replenish molecular species init ially utilized in signal transduction.