The pharmacology of quisqualate and AMPA in the cerebral cortex of the rat in vitro.

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.