EFFECTS OF THE VENOM OF THE THERIDIID SPIDER, STEATODA-CAPENSIS HANN,ON AUTONOMIC TRANSMISSION IN RAT ISOLATED ATRIA AND CAUDAL ARTERY

The possibility of a-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 produce d vasoconstriction in isolated segments of rat caudal artery but was w ithout effect in artery segments obtained from rats that had been pret reated with reserpine (2.5 mg/kg) 24 hr prior to experimentation, indi cating that the vasoconstriction was due to the release of noradrenali ne from periarterial sympathetic nerves. Steatoda capensis Hann VGE al so increased the rate of beating of rat isolated atrial preparations. The positive chronotropic action of the VGE was partly due to the rele ase of noradrenaline from atrial sympathetic nerves since it was reduc ed by the beta-adrenoceptor antagonist propranolol, and smaller increa ses in rate were observed in atria taken from rats pretreated with res erpine. The positive chronotropic effect of the VGE was enhanced by at ropine, suggesting that the VGE also releases acetylcholine from atria l parasympathetic nerves. The VGE evoked release of radioactivity from rat atria in which the transmitter stores of the atrial intramural no radrenergic nerves had been labelled with [H-3]noradrenaline. There ap peared to be two components of the release, one involving omega-conoto xin GVIA-sensitive Ca2+ channels, and the other independent of extrace llular Ca2+.