Inhibitory effect of streptomycin and related antibiotics on the glutamate receptor of the crayfish neuromuscular junction

Abstract

The effect of streptomycin, kanamycin and neomycin on the neuromuscular junction of the crayfish was investigated. Bath application and iontophoretic application of streptomycin depressed the excitatory postsynaptic potential (EPSP) and the glutamate potential. The degree of depression of the EPSP by the action of streptomycin was almost the same as that of the glutamate potential. The inhibitory postsynaptic potential and the γ-aminobutyric acid potential were not changed by strep tomycin. Similar but slightly smaller effects were observed with kanamycin and neomycin. The number of quanta released per impulse was estimated by recording the extracellular EPSP. The quantum content remained almost unchanged during the action of streptomycin, while the quantum size was decreased. The dose-response relationship of l-glutamate estimated from the iontophoretic application was depressed by streptomycin with no apparent parallel shift of the curve. These results suggest that streptomycin acts on the excitatory postsynaptic membrane and depresses the glutamate receptor but shows no effect on the γ-aminobutyric acid receptor.