Studies on ether-phospholipids of vascular smooth muscle cells. Identification of a rapid Ca2+-dependent hydrolysis of alkyl-phosphatidylethanolamine promoted by endothelin-1

We have investigated the metabolism of 1-O-[H-3]octadecyl-sn-glycero-3-phosphocholine ([H-3]lyso PAF) and [3H]myristic acid in secondary cultures of aortic smooth muscle cells (SMC) to characterize the origin of second messengers generated upon stimulation with endothelin-1 (ET-1). When cells were labelled with [H-3]lyso PAF, we observed a transfer of the label from phosphatidylcholine (PC) to phosphatidylethanolamine (PE). In contrast, incubation with [H-3]myristate labelled mainly PC. Both precursors were incorporated into all PC and PE subclasses. However, [H-3]lyso PAF labelled mainly alkyl-subclasses while [H-3]myristate was associated with diacyl-subclasses. Using these specific labelling procedures, we have shown that ET-1 induced a strong hydrolysis of PE. This hydrolysis was specific for alkyl-PE with a maximum after 5 s of stimulation. We have also observed an extracellular Ca2+-dependent increase in diglyceride (DG), phosphatidic acid (PA) and mainly triglyceride (TG) concomitant to alkyl-PE hydrolysis. Thus, alkyl-DG generated from alkyl-PE appears to be a major product in ET-1 stimulation of SMC. These results suggest a new level of complexity in the signal transduction cascade involving a specificity for phospholipid subclasses.