Amino acid pharmacology in neocortical slices: evidence for bimolecular actions from an extension of the Hill and Gaddum-Schild equations.

1. The equivalent circuit of the cortical slice preparation has been analysed to show that the measured d.c. voltages can be used to estimate the Hill coefficient for ligands acting on the pyramidal cell bodies. 2. The Gaddum-Schild equation for agonist-antagonist interactions has been modified for applications in which the Hill coefficient is not equal to 1. 3. The equations obtained have been applied to recent data of Burton et al. (1988). The results provide evidence for a bimolecular action of the agonists N-methyl-D-aspartate (NMDA) and quinolinic acid and the antagonists kynurenic acid and 2-amino-5-phosphono-pentanoic acid at NMDA receptors on mouse neocortical pyramidal cells.