Which toxin increases exocytosis of acetyl choline containing vesicles?

Latrodectus mactans (Black Widow or Hourglass Spider) This is found all over the world. The female of the species is larger and more vicious. There is usually a red hourglass spot on the dorsal surface of its shiny black body. The venom is predominantly neurotoxic and therefore does not produce much local necrosis and some persons experience no other symptoms except a sharp pinprick. However, a-latrotoxin, the most active component of the venom, binds irreversibly to nerves and causes release and eventual depletion of acetylcholine, norepinephrine and other neurotransmitters from presynaptic terminals. Within an hour or so, painful cramps spread from the bite site to large muscles of the extremities and the trunk. Other features may include salivation, diaphoresis, vomiting, hypeension, tachycardia, laboured breathing, anxiety, headache, fasciculations, paraesthesia, hyper-reflexia, urinary retention, uterine contractions and premature labour. Rhabdomyolysis and renal failure have been repoed. Ref : Krishnan vij Textbook of Forensic medicine and Toxicology 5th edtion ; pg no - 487