Postsynaptic block of a glutamatergic synapse by low molecular weight fractions of spider venom.

Fractions of low molecular weight (ca. 600-1000 dalton) isolated by high performance liquid chromatography (HPLC) and thin layer chromatography (TLC) from the venoms of the New-World spiders, Argiope trifasciata and Araneus gemma block transmission at glutamatergic nerve-muscle junctions in the locust, Schistocerca gregaria. These fractions are probably small peptides containing phenolic or indolic residues. Their effects on the neurally evoked twitch contraction, the junctional potential to glutamate ionophoresis and the voltage-clamped excitatory postsynaptic current of locust muscle indicate uncompetitive antagonism of the glutamate receptor channel complex through open channel block. In view of their slow reversibility of action they should make useful tools for future biochemical studies of locust glutamate receptors.