THE HUMAN N-METHYL-D-ASPARTATE RECEPTOR 2C SUBUNIT - GENOMIC ANALYSIS, DISTRIBUTION IN HUMAN BRAIN, AND FUNCTIONAL EXPRESSION

cDNAs encoding four isoforms of the human NMDA receptor (NMDAR) NMDAR2 C (hNR2C-1, -2, -3, and -4) have been isolated and characterized. The overall identity of the deduced amino acid sequences of human and rat NR2C-1 is 89.0%. The sequences of the rat and human carboxyl termini ( Gly(925)-Val(1,236)),re encoded by different exons and are only 71.5% homologous. In situ hybridization in human brain revealed the expressi on of the NR2C mRNA in the pontine reticular formation and lack of exp ression in substantia nigra pars compacta in contrast to the distribut ion pattern observed previously in rodent brain. The pharmacological p roperties of hNR1A/2C were determined by measuring agonist-induced inw ard currents in Xenopus oocytes and compared with those of other human NMDAR subtypes. Glycine, glutamate, and NMDA each discriminated betwe en hNR1A/2C-1 and at least one of hNR1A/2A, hNR1A/2B, or hNR1A/2D subt ypes, Among the antagonists tested, CGS 19755 did not significantly di scriminate between any of the four subtypes, whereas 5,7-dichlorokynur efiic acid distinguished between hNR1A/2C and hNR1A/2D. Immunoblot ana lysis of membranes isolated from HEK293 cells transiently transfected with cDNAs encoding hNR1A and each of the four NR2C isoforms indicated the formation of heteromeric complexes between hNR1A and all four hNR 2C isoforms, HEK293 cells expressing hNR1A/2C-3 or hNR1A/2C-4 did not display agonist responses. In contrast, we observed an agonist-induced elevation of intracellular free calcium and whole-cell currents in ce lls expressing hNR1A/2C-1 or hNR1A/2C-2. There were no detectable diff erences in the macroscopic biophysical properties of hNR1A/2C-1 or hNR 1A/2C-2.