GABA-gated anion channels in intact crayfish opener muscle fibres and stretch-receptor neurons are neither activated nor desensitized by glutamate.

The influence of glutamate on the GABA-activated Cl- conductance was studied in the slowly adapting stretch-receptor neuron and dactylopodite opener muscle fibre of the crayfish (Astacus astacus) using a two-microelectrode and a three-microelectrode voltage clamp, respectively. Glutamate (0.5-1.0 mM) had no effect on the GABA-activated conductance in either preparation. This indicates that the availability of the inhibitory channels for activation of GABA is not influenced by glutamate. The present results are in sharp contrast to those obtained by Franke et al. (J Comp Physiol A 159:591-609, 1986) in experiments on excised membrane patches, which suggested that glutamate is capable of both activating and desensitizing inhibitory postsynaptic channels in the crayfish opener muscle fibre.