MOLECULAR-CLONING, EXPRESSION, AND PHARMACOLOGICAL CHARACTERIZATION OF HUMEAA1, A HUMAN KAINATE RECEPTOR SUBUNIT

Kainate is a potent neuroexcitatory agent; its neurotoxicity is though t to be mediated by an ionotropic receptor with a nanomolar affinity f or kainate. In this report, we describe the cloning of a cDNA encoding a human glutamate ionotropic receptor subunit protein from a human hi ppocampal library. This cDNA, termed humEAA1, is most closely related to rat and human cDNAs for kainate receptor proteins and, when express ed in COS or Chinese hamster ovary cells, is associated with high-affi nity kainate receptor binding. We have successfully established cell l ines stably expressing humEAA1 This is the first report of establishme nt of stable cell lines expressing a glutamate receptor subunit. The r elative potency of compounds for displacing [H-3]kainate binding of hu mEAA1 receptors expressed in these stable cell lines was kainate > qui squalate > domoate > L-glutamate much greater than lpha-amino-3-hydrox y-5-methyl-4-isoxazolepropionic acid > dihydro-kainate > 6,7-dinitroqu inoxaline-2,3-dione > 6-cyano-7-nitroquinoxaline-2,3-dione. Homooligom eric expression of humEAA1 does not appear to elicit ligand-gated ion channel activity. Nevertheless, the molecular structure and pharmacolo gical characterization of high-affinity kainate binding of the humEAA1 expressed in the stable cell line (ppEAA1-16) suggest that the humEAA 1 is a subunit protein of a human kainate receptor complex.