Black widow spider toxin-induced calcium fluxes and transmitter release in a neurosecretory cell line

Several polypeptide neurotoxins affect presynaptic functions by interfering with chemical neurotransmission. This group of toxins includes botulinum toxin, tetanus toxin, ?-bungarotoxin and black widow spider toxin (BWSTx). While the effect of the first three toxins is mainly a rapid and severe block of neurotransmitter release, BWSTx affects transmission by a massive stimulation of mediator release. Despite various hypotheses put forward to explain the action of BWSTx at the level of nerve terminals, there is still a considerable degree of uncertainty as to the action dependence of venom action. Study of the toxin mode of action at the biochemical level has been hampered by the complexity and cellular heterogeneity of the preparations used, neuromuscular junction or synaptosomes. PC12 cell line, derived from a rat phaeochromocytoma, seems to be an excellent model in view of its property of synthesising and storing noradrenaline, dopamine and acetylcholine, and releasing them in depolarising conditions. We have recently shown that highly purified BWSTx stimulates secretion from PC12 cells of previously taken up radioactive dopamine (DA) and noradrenaline (NA). We report here that the earliest detectable event after toxin treatment of such cells is a massive increase of cytosolic calcium.