NEUROMUSCULAR BLOCK IN LOCUST SKELETAL-MUSCLE CAUSED BY A VENOM PREPARATION MADE FROM THE DIGGER WASP PHILANTHUS-TRIANGULUM F FROM EGYPT

A preparation from P. triangulum F. made by extracting abdomens and purified by Sephadex filtration does not affect K ion-induced contractions of the retractor unguis muscle of Schistocerca gregaria Forskal, but reduction of glutamate contractions is at least as pronounced as the effect on the neurally-evoked twitch. Glutamate potentials are affected at a lower venom dose than are the neurally evoked excitatory postsynaptic potentials (EPSPs). The 1/2-decay-time of the glutamate potentials starts to decrease just before the decrease in amplitude is initiated. In the retractor unguis muscle the resting plasma membrane is slightly depolarized at high venom concentrations, but this effect cannot explain the effects on neuromuscular transmission. The venom preparation of P. triangulum probably affects the glutamate or transmitter-induced transient permeability change, possibly by blocking open ion channels.