Fig. 7.
Most native NMDA receptors are potentiated by TPEN. A, Comparison of the effects of TPEN (1 μm) on the peak amplitude of NMDA currents recorded in neurons and in HEK 293 cells expressing either NR1a–NR2A or NR1a–NR2B receptor subtypes. Native NMDA responses were elicited by a 2 sec pulse of NMDA (200 μm) on a background of glycine (10 μm). Recombinant NMDA responses were recorded with protocols identical to those shown in Figure 1. The holding potential was −50 mV. Each circle corresponds to the peak ratio (TPEN/control) obtained from one experiment. Thefilled and hatched circles correspond to the two separate experiments, which are illustrated inB. The potentiation of native NMDA responses by TPEN was highly variable, with peak ratios ranging from 1.0 (no potentiation) to a maximum of 1.6. The mean value was 1.25 ± 0.17 (n = 12). The mean peak ratios for NR1a–NR2A and NR1a–NR2B receptors were 2.9 ± 0.3 (n = 6) and 1.07 ± 0.04 (n = 6), respectively.B, Variability of the effect of TPEN on neuronal NMDA responses. Shown are superimposed traces recorded in the control solution and in the presence of 1 μm TPEN. Eachtrace is the average of three individual responses. Thetop panel shows an example with a marked potentiation by TPEN (the peak ratio TPEN/control of 1.41 corresponds to thefilled circle in A), whereas thebottom panel shows an example in which TPEN was ineffective (the peak ratio of 1.0 corresponds to the hatched circle in A).