SUBCELLULAR-LOCALIZATION AND MOLECULAR PHARMACOLOGY OF DISTINCT POPULATIONS OF [H-3] AMPA BINDING-SITES IN RAT HIPPOCAMPUS

1 The subcellular distributions of [H-3]-alpha-amino-3-hydroxy- 5-methylisoxazolepropionate ([H-3]-AMPA) and [H-3]-kainate binding sites in rat hippocampus were investigated by cell fractionation techniques. 2 Two major populations of [H-3]-AMPA sites were detected with the majority of binding located intracellularly in the microsomal (P-3) fraction. Most of the remaining sites were in the synaptosomal membrane fraction but some were also present in the nuclear fraction. In contrast, essentially all of the [H-3]-kainate binding sites were in the synaptosomal membrane fraction. 3 Saturation binding analysis yielded K-D and B-max values for [H-3]-AMPA of 147 nM and 2.6 pmol mg(-1) protein respectively for the synaptosomal membrane-associated sites and 129 nM and 5.3 pmol mg(-1) protein respectively for the microsomal sites. 4 Both main populations of [H-3]-AMPA sites displayed the same rank order of inhibition by competitive ligands, the apparent Mr values of GluR1 subunits were equivalent, suggesting the same degree of post-translational modification and the hydrodynamic properties of the receptor complexes were identical. 5 These data are consistent with the hypothesis that the movement of AMPA receptors between cellular compartments in the postsynaptic neurone could constitute one mechanism underlying long-term potentiation in the hippocampus.