The action of leucomyosuppressin (LMS: pGlu-Asp-Val-Asp-His-Val-Phe-Leu-Arg-Phe-NH2) on the glutamate-mediated neuromuscular transmission in the mealworm, Tenebrio molitor, was studied by the microelectrode current-clamp and voltage-clamp techniques. Submicromolar concentrations of LMS reversibly attenuate evoked release of transmitter from the motor nerve terminals, as evidenced by a decrease in the quantum content estimated by the number of failures of extracellular EPSPs. LMS has no effect on the glutamate-induced depolarization. Possible intracellular mediators for the LMS action are discussed.
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