Effects of the venom of the theridiid spider, Steatoda capensis Hann, on autonomic transmission in rat isolated atria and caudal artery.

The possibility of alpha-latrotoxin-like activity in the crude venom gland extract (VGE) of a related Theridiid spider, Steatoda capensis Hann, was investigated. The VGE from female S. capensis Hann spiders produced vasoconstriction in isolated segments of rat caudal artery but was without effect in artery segments obtained from rats that had been pretreated with reserpine (2.5 mg/kg) 24 hr prior to experimentation, indicating that the vasoconstriction was due to the release of noradrenaline from periarterial sympathetic nerves. Steatoda capensis Hann VGE also increased the rate of beating of rat isolated atrial preparations. The positive chronotropic action of the VGE was partly due to the release of noradrenaline from atrial sympathetic nerves since it was reduced by the beta-adrenoceptor antagonist propranolol, and smaller increases in rate were observed in atria taken from rats pretreated with reserpine. The positive chronotropic effect of the VGE was enhanced by atropine, suggesting that the VGE also releases acetylcholine from atrial parasympathetic nerves. The VGE evoked release of radioactivity from rat atria in which the transmitter stores of the atrial intramural noradrenergic nerves had been labelled with [3H]noradrenaline. There appeared to be two components of the release, one involving omega-conotoxin GVIA-sensitive Ca2+ channels, and the other independent of extracellular Ca2+.