FUNCTIONAL EXPRESSION AND PHARMACOLOGICAL CHARACTERIZATION OF THE HUMAN EAA4 (GLUR6) GLUTAMATE-RECEPTOR - A KAINATE SELECTIVE CHANNEL SUBUNIT

A cDNA encoding an ionotropic glutamate receptor subunit protein humEA A4 (GluR6), has been cloned from a human fetal brain library. This cDN A when expressed in COS or HEK-293 cells is associated with high-affin ity kainate receptor binding and ion channel formation. We have succes sfully established cell lines stably expressing humEAA4, in HEK-293 ce lls. This is the first report of the establishment of stable cell line s expressing a glutamate receptor channel. The relative potency of com pounds for displacing [H-3]-kainate binding to humEAA4 receptors expre ssed in COS or HEK-293 cells is domoate > kainate > quisqualate > 6-cy ano-7-nitroquinoxaline-2,3-dione > L-glutamate = 6,7-dinitroquinoxalin e2,3-dione > dihydrokainate. Applications of kainate, glutamate, and d omoate but not AMPA evoked rapidly desensitizing currents in cells exp ressing homo-oligomeric humEAA4 in a concentration dependent manner. T he order of potency was: domoate > kainate > L-glutamate. Although AMP A did not itself activate humEAA4 receptors it did reduce, to a limite d extent, kainate-evoked responses. AMPA may therefore be a weak parti al agonist for this receptor. To date this effect has not been demonst rated with rat GluR6. It is possible that subtle species differences m ay exist in the nature of agonist receptor interaction. Kainate evoked currents were attenuated by the quinoxalinediones CNQX and DNQX but n ot by DAP5. The receptor desensitization was attenuated on application of concanavalin A. Ion-permeability studies indicated that the recept or-linked ion channel is permeable to both Na+ and Ca2+ ions.