Arachidonic acid metabolism in articular chondrocytes

In this study rabbit articular chondrocytes were cultured and the cells were labeled with 3H-arachidonic acid and 14C-stearic acid. 3H incorporation reached a plateau at four hours and 14C-incorporation reached a plateau at 24 hours. The 3H was associated mainly with phosphatidylcholine (PC), phosphatidylethanolamine (PE), and phosphatidylinositol (PI) at the 2-position while 14C was found at the 1-position. When the double-labeled cells were incubated with bradykinin or ionophore A23187, a significant release of 3H into the medium was observed, while the 14C release was small. Approximately 90% of the 3H released was arachidonic acid. Small amounts of the released 3H were no longer associated with stearic acid; it was converted mainly into prostaglandin E2 (PGE2). When stimulated by either bradykinin or ionophore, a significant 3H loss was observed in cellular PC while there were no significant 3H changes in other phospholipids, triacylglycerols (TGs), or diacylglycerols (DGs). Although 14C of cellular lysophosphatidylcholine (lyso-PC) was not increased significantly, the 3H seemed to be released from the 2-position of PC by the action of phospholipase A2. There was no significant change in the breakdown of PC between palmitoyl-arachidonyl (16:0/20:4) and stearoyl-arachidonyl (18:0/20:4) species. Both A23187 and bradykinin may activate phospholipase A2, releasing arachidonic acid equally from the 2-position of PCs having either palmitic acid or stearic acid at the 1-position. Some of this material is converted to PGE2, but this conversion is low compared to other cell types.