Binding of DL-[3H]-alpha-amino-3-hydroxy-5-methyl-isoxazole-4-propionic acid (AMPA) to rat cortex membranes reveals...

A method for measuring [3H]-AMPA binding in rat cortex membranes is described. Specific binding was saturable and accounted for 95% of total binding at 5 nM of [3H]-AMPA. Non linear curve fitting of [3H]-AMPA saturation isotherms suggested the presence of two binding sites: the high affinity site showed a pKd of 8.26 +/- 0.07 (Kd = 5.49 nM) and a Bmax of 0.19 +/- 0.03 pmol/mg protein, whereas the low affinity site indicated a pKd of 7.28 +/- 0.05 (Kd = 52 nM) and a Bmax of 1.30 +/- 0.23 pmol/mg protein. The pharmacological profile of [3H]-AMPA binding has been determined by studying a series of compounds in binding displacement experiments: Quisqualate was the most potent inhibitor of [3H]-AMPA binding (IC50 = 9.7 nM), followed by AMPA (19 nM), CNQX, DNQX and L-Glutamate (272-373 nM). Kainate was a moderate displacer (6.2 microM); Ibotenic acid and glycine were very weak inhibitors (74 and 92 microM, respectively). CPP, GAMS and L-Aspartic acid showed IC50-values of over 400 microM and MK-801, DL-AP5 and NMDA were almost inactive at the maximal concentration used in our experiments.