Slowly-reversible block of glutamate receptor-channels by venoms of the spiders, Argiope trifasciata and Araneus gemma.

Venom from two species of spider has been tested on the locust glutamatergic nerve-muscle system. The neurally-evoked twitch contraction of locust metathoracic retractor unguis muscle was abolished in the presence of venom and only slowly recovered following its removal. The twitch inhibition onset rate was venom concentration and stimulation frequency dependent. The mechanical response of this muscle to L-glutamate was also inhibited by spider venom. Complete abolition of the potential evoked by ionophoresis of L-glutamate to excitatory junctions on locust metathoracic extensor tibiae muscle was obtained with low concentrations of venom and recovery on washing was either slow and incomplete or not evident. The ionophoretic studies and twitch contraction studies indicate that the venom acts only when the glutamate receptor channel complex is activated by agonist. This conclusion is supported by data of the effects of venom on the voltage clamped excitatory postsynaptic current recorded from locust extensor tibiae muscle. Preliminary attempts to identify and isolate the active principles in these spider venoms indicate that activity is restricted to a molecule(s) of low (less than 1000 dalton's) molecular weight.