Evidence for a tetrameric structure of recombinant NMDA receptors - PubMed (original) (raw)

Membrane currents in oocytes expressing heteromeric NMDA receptors generated by coinjection of NR1, NR1Q387K, and NR2B subunits. A, Glycine-activated whole-cell currents in the presence of 100 μ

ml

-glutamate obtained at a holding potential of −70 mV. Oocytes injected with the wt NR1 and NR1Q387K cRNAs at a ratio of 1:1 were superfused with the glycine concentrations indicated above the application bars. Calibration: 200 nA, 15 sec. B, Glycine dose–response curves obtained from oocytes injected with NR1 and NR1Q387K (•) cRNAs at ratio of 1:1. Note the triphasic dose–response seen on coexpression of the wt and mutant NR1 subunits. Corresponding EC50 values for the high-affinity (HA), intermediate-affinity (IMA), and low-affinity (LA) components are 0.56 μ

m

, 48 μ

m

and 4.8 m

m

, with fractional contributions of 27, 44, and 29% of the maximal current, respectively. C, Glycine dose–response curves recorded from oocytes injected with the NR1 and NR1Q387KcRNAs at a ratios of 5:1 (▪) or 1:5 (▴), respectively. In both cases, clearly biphasic dose–response curves were obtained. The corresponding EC50 values of the HA- and IMA-, or IMA- and LA- components are 0.9 and 50 μ

m

, or 84 μ

m

and 7 m

m

, with fractional current contributions of 79 and 21%, or 26 and 74%, respectively, of the maximal current. In both_B_ and C, the _solid lines_represent least-squares fits of the data to the modified Hill Equation2. The dotted lines correspond to the dose–response curves of the pure NR1/NR2B and NR1Q387K/NR2B HA- and LA-components. Data from individual oocytes are shown; all measurements were repeated on at least three different oocytes with similar results. The mean (± SD) of the EC50 values and the Hill coefficients calculated from these experiments are given in Table 1. The subunit compositions predicted for tetrameric receptor complexes are indicated schematically (○ represents NR1 wt, • NR1Q387K, and ◍ NR2B).