Source of the arachidonic acid released on stimulation of rat basophilic leukemia cells

Triggering of rat basophilic leukemia cells for histamine secretion is accompanied by arachidonic acid release. We studied the source of this arachidonic acid released after IgE or calcium ionophore A23187 stimulation. The 48-hr culture of the cells with [14C]arachidonic acid resulted in labeling of the phospholipids to constant specific activity. After IgE stimulation, 8.8% of the cellular [14C]arachidonate was released; this was predominantly from phosphatidylinositol (PI)/phosphatidylserine (PS) (66.3%), less from phosphatidylethanolamine (PE) (25.9%), and minimally from phosphatidylcholine (PC). In contrast, after ionophore stimulation the cells released 16.4% of cellular [14C]arachidonate, most of this was from PE (55.4%) followed by about equal amounts from PS/PI and PC (24% and 20%, respectively). Therefore, the source of the released arachidonic acid depends on the stimulus. In contrast, the results are different when the cells are cultured for only 2 hr with [14C]arachidonic acid. The label in phospholipids was in PC (44%), PE (38%), and PI/PS (20%); the stimulation of the cells with IgE or ionophore resulted in the release of the [14C]arachidonate from PC (81% and 96%, respectively). This suggests the presence of several pools of phospholipids that are labeled at different rates and have variable proximity and/or accessibility to the phospholipase(s) enzyme(s) activated during cell secretion.