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 cul tures of aortic smooth muscle cells (SMC) to characterize the origin o f 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 phosphatidylethanolamin e (PE). In contrast, incubation with [H-3]myristate labelled mainly PC . Both precursors were incorporated into all PC and PE subclasses. How ever, [H-3]lyso PAF labelled mainly alkyl-subclasses while [H-3]myrist ate was associated with diacyl-subclasses. Using these specific labell ing 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+-dependen t increase in diglyceride (DG), phosphatidic acid (PA) and mainly trig lyceride (TG) concomitant to alkyl-PE hydrolysis. Thus, alkyl-DG gener ated from alkyl-PE appears to be a major product in ET-1 stimulation o f SMC. These results suggest a new level of complexity in the signal t ransduction cascade involving a specificity for phospholipid subclasse s.