title: Effects of beta-bungarotoxin and Naja naja atra snake venom phospholipase A2 on acetylcholine release and choline uptake in synaptosomes.
abstract: 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 synaptosomal 3H-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. Therefore, beta-bungarotoxin and N. naja atra phospholipase A2 block 3H-acetylcholine release from synaptosomes indirectly by inhibiting the uptake of 3H-choline necessary for 3H-acetylcholine synthesis. In comparing these results using 3H-choline to those in the literature obtained with deuterated choline, there appears to be a difference in apparent toxin action that relates to the type of label (3H or 2H) attached to choline.
mesh_terms: D000109:Acetylcholine / Q000378:metabolism*; D000818:Animals; D002038:Bungarotoxins / Q000494:pharmacology*; D002540:Cerebral Cortex / Q000378:metabolism; D002794:Choline / Q000378:metabolism*; D004546:Elapid Venoms / Q000494:pharmacology*; D005260:Female; D006168:Guinea Pigs; D066298:In Vitro Techniques; D007700:Kinetics; D010740:Phospholipases / Q000494:pharmacology*; D010741:Phospholipases A / Q000494:pharmacology*; D054467:Phospholipases A2; D013574:Synaptosomes / Q000187:drug effects / Q000378:metabolism*
chemical_list: D002038:Bungarotoxins; D004546:Elapid Venoms; D010740:Phospholipases; D010741:Phospholipases A; D054467:Phospholipases A2; D002794:Choline; D000109:Acetylcholine