Involvement of phospholipase A(2) in norepinephrine release from synaptosomes isolated from rat cerebral cortex

Phospholipase A(2) added directly to superfused [(3)H]norepinephrine-labeled synaptosomes could cause the release of neurotransmitter molecules. Chloroquine and quinacrine, which block the action of phospholipase A(2), inhibited either the phospholipase A(2)-stimulated or the high potassium-stimulated release of [(3)H]norepinephrine from synaptosomes. Only quinacrine blocked the high potassium-stimulated influx of Ca(2+). It appears that during stimulation of synaptosomes, Ca(2+) influx leads to the activation of phospholipase A(2), which in turn, hydrolyzes membrane phospholipids in situ. The formation of lysophospholipids may alter the microenvironment and the physicochemical properties of membranes, resulting in the release of neurotransmitter through exocytosis.