THE CALCIUM-DEPENDENT TRANSIENT INACTIVATION OF RECOMBINANT NMDA RECEPTOR-CHANNEL DOES NOT INVOLVE THE HIGH-AFFINITY CALMODULIN-BINDING SITE OF THE NR1 SUBUNIT

N-methyl-D-aspartate (NMDA) receptor function can be regulated by dire ct binding of calmodulin to a low and high affinity (C1 exon cassette) site in the C-terminal region of the NR1 subunit. To evaluate the inv olvement of the high affinity binding site in the transient inactivati on of the NMDA receptor-channels by intracellular calcium, several spl ice variants of the NR1 subunit have been individually co-transfected with the NR2A subunit in HEK 293 cells. The transient Ca2+ induced ina ctivation (40-50%) of the heteromeric receptors was similar whether th e NR1 variants contained (NR1-1a, 1b) or lacked (NR1-2a, 2b, 4a, 4b) t he C1 exon cassette bearing the high affinity binding site for calmodu lin. This demonstrates that this site is not involved in the Ca2+ depe ndent transient inactivation of NMDA receptors. (C) 1997 Elsevier Scie nce Ireland Ltd.