An NR2B point mutation affecting haloperidol and CP101,606 sensitivity of single recombinant N-methyl-D-aspartate...

Haloperidol and ifenprodil are N-methyl-D-aspartate (NMDA) receptor (NR) antagonists with preference for the NR1/NR2B subunit combination. Previous investigations utilizing 125I-MK801 binding assays with recombinant receptors distinguished certain structural determinants on the NR2B subunit for these two drugs, with glutamate 201 being critical for haloperidol sensitivity and arginine 337 being important for ifenprodil block. Other studies, however, suggested that these two sites pharmacologically overlap. In an attempt to resolve these discrepancies, we have characterized the actions of haloperidol and CP101,606, an ifenprodil analog, on the single-channel properties of NR1/NR2B(E201R) receptors transiently expressed in Chinese hamster ovary cells, because receptors formed by NR1/NR2B(R337K) appear to be nonfunctional. Haloperidol (10 microM) inhibited wild-type NR1/NR2B channels by decreasing the frequency of channel opening, whereas CP101,606 (0.5 microM) antagonized NR1/NR2B channel activity by decreasing both the open dwell time and the frequency of channel opening. The inhibitory actions of both drugs were virtually absent in the mutant NR1/NR2B(E201R) receptors. These results suggest that glutamate 201 is critical for both haloperidol and CP101,606 inhibition, thus demonstrating common features in the action of these two antagonists.