Release of glutamate from the crayfish neuromuscular junction.

Abstract

The superficial abdominal slow flexor muscle was isolated from the crayfish (C. clarkii) and placed in a bath solution of 100 .mu.l. The concentration of glutamate in this solution was measured by mass fragmentography using a gas chromatograph-mass spectrometer. The excitatory post-synaptic potential (e.p.s.p.) of the low flexor muscle and its sensitivity to L-glutamate were similar to those observed in the opener muscle of the dactyl in the walking leg or claw of the crayfish. The background efflux of glutamate during control rest periods was .apprx. 20 p-mol/10 min. Nerve stimulation caused a significant increase in the efflux of glutamate. The net release of glutamate above the background was 11.9 p-mol/100 .mu.l at 10 Hz stimulation and 21.1 p-mol/100 .mu.l at 20 Hz stimulation. When the amplitude of e.p.s.p. was decreased by streptomycin, thereby reducing the muscle contraction, the net release of glutamate by nerve stimulation was unchanged. Streptomycin depressed the e.p.s.p. by its action on the post-synaptic membrane. When the external concentration of Ca was lowered, the amplitude of e.p.s.p. and the net release of glutamate were decreased. L-glutamate is released from the nerve terminals of the crayfish neuromuscular junction.