Rapid acylation and deacylation of arachidonic acid into phosphatidic acid of horse neutrophils

Abstract

Horse neutrophils incorporate exogenous [14C]arachidonate into phosphatidic acid very rapidly. This acylation of phosphatidate with arachidonate is followed quickly and spontaneously by its deacylation. This transient formation of arachidonyl-phosphatidate, which reflects a rapidly turning over pool of arachidonate-associated lipid, is not observed with stearic acid or other phospholipids or triglycerides. Phosphatidylcholine, phosphatidylethanolamine, phosphatidylinosinositol, and triglycerides are slowly but increasingly labeled with time. Ionophore A23187 (10 microM) stimulates the extent of labeling of phosphatidate while decreasing the labeling of all the other phospholipids and triglycerides. Phosphatidate is not transiently labeled with [14C]stearate of (32P)orthophosphate, either in the presence or absence of ionophore A23187. When cells are prelabeled for 2 h with very high quantities of (32P)orthophosphate a very substantial fraction (i.e. 20 to 30%) of the phospholipid radioactivity is associated with phosphatidic acid. However, on addition of exogenous arachidonate, there is no increase in [32P]phosphatidate in these prelabeled cells. Thus, the entire phosphatidate molecule does not appear to be turned over during the process described above. Inhibitors of cyclooxygenase and lipoxygenase activities such as BW755C, nordihydroguaiaretic acid, and low concentrations of indomethacin do not affect the labeling of phospholipids. However, eicosatetraynoic acid, an analog of arachidonate, and high concentration (0.1 mM) of indomethacin can block [14C]arachidonate incorporation into lipids. The rapid turnover of the 2-acyl position in phosphatidate might be related to a specific process of fatty acid mobilization within neutrophils.