[H]ATPA: a high affinity ligand for GluR5 kainate receptors

The pharmacological properties of [³H]ATPA ((RS)-2-amino-3(3-hydroxy-5-tert-butylisoxazol-4-yl)propanoic acid) are described. ATPA is a tert-butyl analogue of AMPA (-amino-3-hydroxy-5-methyl-4-isoxazoleproprionic acid) that has been shown to possess high affinity for the GluR5 subunit of kainate receptors. [³H]ATPA exhibits saturable, high affinity binding to membranes expressing human GluR5 (GluR5) kainate receptors (K_d13 nM). No specific binding was observed in membranes expressing GluR2 and GluR6 receptors. Several compounds known to interact with the GluR5 kainate receptor inhibited [³H]ATPA binding with potencies similar to those obtained for competition of [³H]kainate binding to GluR5. Saturable, high affinity [³H]ATPA binding (K_d4 nM) was also observed in DRG neuron (DRG) membranes isolated from neonatal rats. The rank order potency of compounds to inhibit [³H]ATPA binding in rat DRG and GluR5 membranes were in agreement. These finding demonstrate that [³H]ATPA can be used as a radioligand to examine the pharmacological properties of GluR5 containing kainate receptors.