The depolarising population response to the excitatory amino acids, quisqualate and AMPA, in slices of cerebral cortex of the rat have been compared. Their respective dose-response curves had a similar maximum but the slope of the curve for AMPA was consistently steeper than that for quisqualate. The dose-response curves for AMPA had a mean log EC50 of -5.18 +/- 0.05, which was significantly different from -4.62 +/- 0.07 the mean log EC50 of the dose-response curves for quisqualate. Responses to both agonists were antagonised by kynurenic acid, barbiturates and gamma-DGT to a similar extent. The antagonism by kynurenate appeared to be competitive whilst the barbiturates were evidently noncompetitive antagonists. These results are in agreement with claims that quisqualate and AMPA act at a similar recognition site. The differences in the slopes of the dose-response curves for quisqualate and AMPA may be explained by the differences in the cellular uptake of the two agonists and/or by differences in efficacy.
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