CDNA CLONING AND FUNCTIONAL-PROPERTIES OF HUMAN GLUTAMATE-RECEPTOR EAA3 (GLUR5) IN HOMOMERIC AND HETEROMERIC CONFIGURATION

We have isolated a new member of the human glutamate receptor family f rom a fetal brain cDNA library. This cDNA clone, designated EAA3a, sha res a 90% nucleotide identity with the previously reported rat GluR5-2 b cDNA splice variant and differed from human GluR5-1d in the amino an d carboxy terminal regions. Cell lines stably expressing EAA3a protein formed homomeric ligand-gated ion channels responsive, in order of de creasing affinity to domoate, kainate, L-glutamate and alpha-amino-3-h ydroxy-5-methylisoxazole-propionate (AMPA). Kainate-evoked currents sh owed partial desensitization that was reduced on incubation with conca navalin A (conA) but not cyclothiazide and were attenuated by the non- N-methyl-D-aspartate (NMDA) receptor antagonist CNQX (6-cyano-7-nitro- quinoxalinedione). Coexpression of EAA3a and human EAA1 cDNAs in HEK 2 93 cells formed a heteromeric channel with unique properties. Kainate and AMPA activated the heteromeric channel with significantly higher a ffinities than observed for EAA3a alone. Ligand binding studies with t he recombinant EAA3a receptor expressed in mammalian cells indicated a high affinity kainate binding site (K-d = 120 +/- 15.0 nM). The relat ive potency of compounds in displacing [H-3]-kainate binding to EAA3a receptor was: domoate > kainate > L-glutamate = quisqualate > 6,7-dini troquinoxaline-2,3-dione (DNQX) = CNQX > AMPA > dihydrokainate > NMDA.