Activation of diacylglycerol in cultured endothelial cells exposed to cyclic strain

Confluent bovine aortic endothelial cells (EC) were grown on flexible membranes and subjected to 10% average strain at 60 cycles/min for up to 500 a. A biphasic increase in diacylglycerol (DAG) occurred, with an initial transient peak at 10 s followed by sustained elevation to 500 s. The early peak corresponded to the transient formation of inositol 1,4,5-trisphosphate, demonstrating hydrolysis of L-alpha-phosphatidylinositol (PI) by PI-specific phospholipase C. To determine the origin of the sustained DAG phase, we incubated confluent bovine aortic EC with I mu Ci/ml [C-14]myristate overnight and subjected them to cyclic strain. There was a decrease in phosphatidylcholine (PC) and a corresponding increase in DAG at 10 s and 250 s: suggesting PC hydrolysis with the generation of DAG at both an early (10 s) and a late (250 s) phase. [C-14]phosphatidylethanol, a specific product of phospholipase D (PLD) in the presence of 1% ethanol, was measured in EC preincubated with [C-14]myristate. Cyclic strain led to an immediate and sustained activation of PLD. Increased ethanol concentration led to a consistent decrease in DAG. Furthermore, when EC were pretreated with 1% ethanol, the strain-induced proliferative response was attenuated.