Stimulation of cytosolic phospholipase A2-catalyzed arachidonic acid liberation by low dose tert-butyl hydroperoxide without an influence on the enzyme activity in rabbit platelets.

The effect of lipid peroxide on the hydrolytic action of cytosolic phospholipase A2 (cPLA2) in rabbit platelets was investigated. Ionomycin-stimulated arachidonic acid liberation and lysophosphatidylcholine formation were significantly potentiated when platelets were pretreated with tert-butyl hydroperoxide (BHP) and FeSO4, and then washed. Under the conditions, oxidizing reagents did not enhance the increase in cPLA2 activity by ionomycin or the basal activity in unstimulated cells. Furthermore, the treatment of a platelet lysate with BHP and FeSO4 did not affect Ca(2+)-induced translocation of cPLA2 to the membranes. However, with a membrane fraction, arachidonic acid liberation catalyzed by the partially purified cPLA2 was synergistically enhanced by BHP and FeSO4. These results suggest that oxidative stress may potentiate the hydrolytic action of cPLA2 on membrane phospholipids without an influence on the processes leading to the enzyme activation.