The binding of [3H]AMPA, a structural analogue of glutamic acid, to rat brain membranes.

Binding of [3H]AMPA to rat brain membranes was investigated. The binding was saturable and reversible at physiological pH. Computer-aided Scatchard analysis of the binding data, as determined by using L-glutamic acid (L-GLU) to define nonspecific binding, suggested the presence of two independent binding sites, with KDS of 9 and 2440 nM, respectively. Additional freezing, thawing and washing sequences gave membranes with only one binding site, with a KD of 278 nM. [3H]AMPA binding exhibited the highest level in striatal membranes. A series of analogues of GLU and aspartic acid (ASP) were tested as inhibitors of [3H]AMPA binding. L-ASP and compounds which interact predominantly with N-methyl-D-aspartic acid (NMDA) receptor sites were inactive as inhibitors of [3H]AMPA binding, whereas L-GLU and compounds which interact predominantly with glutamic acid diethyl ester receptor sites were inhibitors with the same order of potency as that shown by the excitatory action in vivo. The result suggests that [3H]AMPA might represent binding to an excitatory GLU receptor.