Phospholipid hydrolysis and loss of membrane integrity following treatment of rat brain synaptosomes with β-bungarotoxin, notexin, and Naja naja atra and Naja nigricollis phospholipase A2

Abstract The effects of the phospholipase A 2 (PLA 2 ) toxins, β-bungarotoxin and notexin, and the PLA 2 enzymes from Naja naja atra and Naja nigricollis snake venoms on the plasma membrane integrity of synaptosomes were examined. Synaptosomes were isolated from rat brain cerebral cortex, corpus striatum and hippocampus. Osmotic activity, lactate dehydrogenase leakage, and leakage of 2-deoxy- d -(1- 3 H)-glucose-6-phosphate were monitored (37°C, 10–120 min) following incubation with 0.5, 5 and 50 nM concentrations of toxins and enzymes. Damage to the synaptosomal plasma membrane was time and concentration but not tissue dependent. The potencies of the treatments were as follows: N . n . atra PLA 2 ≥ N . nigricollis PLA 2 > notexin > β - bungarotoxin . Chelation of Ca 2+ with 5 mM EDTA completely inhibited plasma membrane disruption caused by β-bungarotoxin and N. n. atra PLA 2 . One mg/ml of bovine serum albumin also blocked the disruptive action of N. n. atra PLA 2 , while 8 mg/ml was required to antagonize β-bungarotoxin. A correlation between phospholipid hydrolysis and loss of membrane integrity was also observed. The generation of phospholipid hydrolytic products may be critical in the permeabilization of synaptic plasma membranes by these toxins and enzymes, however, they do not explain the presynaptic specificity and potency of β-bungarotoxin and notexin.