Effects of the Release of Arachidonic Acid from 1-Ether-Linked Phospholipids on Opsonized-Zymosan Stimulated Rabbit Alveolar Macrophages

On rabbit alveolar macrophages prelabeled with double tracers of [3H] arachidonic acid (20 : 4) for 30 min (short-term labeling) and of [14C] 20 : 4 for 12 h (long-term labeling), the relationship between phospholipid subclasses and the release of 20 : 4 on stimulation with opsonized-zymosan (OZ) was investigated. Stimulation with 500μg of OZ/ml for 1h caused a significant decrease in the radioactivity of incorporated [3H] 20 : 4 in all phosphatidylcholine (PC) subclasses of the cells : by 48% in 1-O-alkyl-2-acyl-sn-glycerol-3-phosphocholine (alkylacyl-GPC), and by 24% in 1, 2-diacyl-GPC (diacyl-GPC), and slightly in 1-O-alk-1'-enyl-2-acyl-GPC (alkenylacyl-GPC). In phosphatidylethanolamine (PE), a significant decrease in the incorporated [3H] 20 : 4 was also observed in the 1, 2-diacyl-sn-glycerol-3-phosphoethanolamine (diacyl-GPE, 45%). On the other hand, the radio activity of [14C] 20 : 4 incorporated by long-term labeling into PC decreased significantly, by approximately 40%, in the alkylacyl-GPC and slightly in the alkenylacyl-GPC. In PE, a significant decrease (approximately 32%) in radioactivity of [14C] 20 : 4 was observed only in the alkenylacyl-GPE which incorporated the largest amount of [14C] 20 : 4 among the cellular phospholipids in its labeling and which showed the biggest decrease in [14C] 20 : 4 in the PC and PE subclasses on stimulation with OZ. These results suggest that on OZ stimulation of rabbit alveolar macrophages, PC and PE subclasses involved in the mobilization of 20 : 4 depend on each 20 : 4 pool which is extracted in the cells.