Differential subcellular localization of two populations of glutamate/AMPA receptors in the rat telencephalon

Abstract

The distribution of glutamate AMPA receptors in the synaptosomal and microsomal fractions of neonatal and adult rat telencephalon was studied by determining the saturation kinetics at equilibrium of 3H-AMPA and 3H-CNQX binding. At both ages, synaptosomal preparations exhibited two populations of 3H-AMPA binding sites with a small number of high affinity sites and a large number of low affinity sites. 3H-AMPA binding to microsomal preparations from both neonatal and adult rat telencephalon exhibited a much higher proportion of high affinity relative to low affinity sites. 3H-CNQX binding to the same fractions did not parallel 3H-AMPA binding, but was correlated with the low affinity 3H-AMPA binding and with a marker of plasma membranes. The results suggest that nonsynaptic glutamate/AMPA receptors have a high affinity for agonist and become low affinity when inserted into postsynaptic membranes and that 3H-CNQX binds synaptic but not nonsynaptic glutamate/AMPA receptors with high affinity.