A comparison of sodium-dependent glutamate binding with high-affinity glutamate uptake in rat striatum.

The specific sodium-dependent binding of [3H]glutamate to membranes of the rat striatum was examined and a comparison made with high affinity glutamate uptake. In the presence of sodium, [3H]glutamate binding was saturable and of high affinity. No binding could be detected in the absence of sodium. Removal of the cortical afferents to the striatum resulted in a parallel decrease in Na+-dependent glutamate binding and in high-affinity glutamate uptake. After the injection of the neurotoxin kainic acid into the striatum, the density of Na+-dependent glutamate binding sites was reduced by 40%, while high-affinity uptake showed no significant decrease. Drugs which inhibit high-affinity uptake were also effective at inhibiting Na+-dependent binding. The results suggest that about half the Na+-dependent glutamate binding sites in the striatum represent high-affinity uptake sites on the corticostriatal terminals. The remainder of the binding sites are located on striatal neurons and may also be uptake sites.