β‐Bungarotoxin antagonizes the effect of α‐latrotoxin from black widow spider venom on the neuromuscular junction

Sustained contraction of the chick biventer cervicis nerve‐muscle preparations evoked by α‐latrotoxin was antagonized quickly by β‐bungarotoxin. This effect of β‐bungarotoxin was dependent on its phospholipase A2 activity. In contrast, pancreatic phospholipase A2 was ineffective even at a much higher dose. It is concluded that α‐latrotoxin needs intact presynaptic membrane to exert its effect.