Effects of Beta-Bungarotoxin and Naja naja atra Snake Venom Phospholipase A2 on Acetylcholine Release and Choline Uptake in Synaptosomes

摘要

Effects of beta-bungarotoxin and Naja naja atra snake venom phospholipase A2 on acetylcholine release and choline uptake in synaptosomes. Beta-bungarotoxin is a potent presynaptically acting snake venom toxin that exhibits phospholipase A2 activity. We compared the effects of beta-bungarotoxin and a less toxic snake venom phospholipase A2 on synaptosomal3H-acetylcholine release and 3H-choline uptake. The purpose of these experiments was to study the mode by which beta-bungarotoxin inhibits 3H-acetylcholine release in this preparation. Under non-depolarizing conditions, both beta-bungarotoxin and Naja naja atra phospholipase A2 stimulated 3H-acetylcholine release from a synaptosomal fraction preloaded with 3H-choline. Beta-bungarotoxin was more potent, but less efficacious, than N. naja atra phospholipase A2. In contrast, both toxins inhibited 3H-acetylcholine release from the synaptosomal fraction incubated with 3H-choline after toxin exposure. In agreement with the results obtained by monitoring acetylcholine release, beta-bungarotoxin and N. naja atra phospholipase A2 appeared to block 3H-choline uptake into the synaptosomal fraction non-competitively. Although the toxins may cause the release of unlabeled choline from synaptosomes, the block of labeled choline uptake could not be explained by decreased specific activity of 3H-choline in the bathing medium.