L-glutamate and potassium-induced contractures in denervated cockroach muscles.

1. The effects of denervation on the mechanical responses to various concentrations of L-glutamate in retractor unguis muscle of cockroach (Perilpaneta americana) was examined, comparing them with contractures induced by high potassium saline. 2. The dose-response curve was shifted to the lower concentrations of L-glutamate after 9 days of denervation. 3. Following a transient increase in the maximum contracture tension, it decreased with days after denervation and reached a constant level by several days. However, from 16 to 20 days after denervation, the tension ratios of the maximum glutamate to potassium contractures were significantly higher than that of the innervated muscles. 4. A sustained contracture was observed on and after treatment of L-glutamate in the denervated muscle. Pretreatment of the muscle by concanavalin A facilitated to induce L-glutamate contracture. 5. It was suggested that the sensitivity of the muscle membrane to L-glutamate was increased in the denervated muscle.