Effects of postdecapitative ischemia on arachidonate release from brain synaptosomes

Synaptosomal phosphoglycerides were labeled after incubation with [1-14C]arachidonic acid, ATP, Mg2+, CoASH, and a small amount of 1-acylglycerophosphocholines. Under this incubation system, radioactivity was directed largely to diaclyglycerophosphocholines but diacylglycerophosphoinositols were also labeled to a lesser extent. Synaptosomes obtained after a 5-min ischemic treatment indicated a decrease (10-20%) in incorporation of radioactivity into the phospholipids. The ischemic synaptosomes also tended to retain a larger portion of the labeled arachidonate during the wash with bovine serum albumin. Upon incubation of the prelabeled synaptosomes in a sucrose-Tris (pH 7.4) medium at 37 degrees C, a time-dependent release of labeled arachidonate from the phospholipids was observed in both control and ischemic samples. Arachidonate release from the prelabeled synaptosomes was not affected by EDTA (1 mM) or taurocholate (0.4%) but was stimulated by Ca2+ (2.5 mM) or Ca2+ (3.5 mM) together with EDTA (1 mM). After incubation at 37 degrees C for 1 hr without added factors, the phospholipid degradation, as well as the appearance of free fatty acids, were higher in the ischemic samples (especially after 1 min of treatment) as compared to controls.