OPPOSING CONTRIBUTIONS OF NR1 AND NR2 TO PROTEIN-KINASE-C MODULATION OF NMDA RECEPTORS

N-Methyl-D-aspartate (NMDA) receptors mediate increases in intracellul ar calcium that can be modulated by protein kinase C (PKC), As PKC mod ulation of NMDA receptors in neurons is complex, we studied the effect s of PKC activation on recombinant NMDA receptor-mediated calcium rise s in a nonneuronal mammalian cell line, human embryonic kidney 293 (HE K-293). Phorbol 12-myristate 13-acetate (PMA) pretreatment of HEK-293 cells enhanced or suppressed NMDA receptor-mediated calcium rises base d on the NMDA receptor subunit composition. NR2A or NR2B, in combinati on with NR1(011), conveyed enhancement whereas NR2C and NR2D conveyed suppression. The PKC inhibitor bisindolylmaleimide blocked each of the se effects. The region on NR2A that conveyed enhancement localized to a discrete segment of the C terminus distal to the portion of NR2C tha t is homologous to NR2A. Calcium-45 accumulation, but not intracellula r calcium store depletion, matched PMA effects on NMDA receptor-mediat ed calcium changes, suggesting that these effects were not due to effe cts on intracellular calcium stores. The suppression of intracellular calcium transients seen with NR2C was eliminated when combined with NR 1 splice variants lacking C-terminal cassette 1. Thus, the intracellul ar calcium effects of PMA were distinguishable based on both the NR1 s plice variant and the NR2 subunit type that were expressed. Such diffe rential effects resemble the diversity of PKC effects on NMDA receptor s in neurons.