Figure 3

Comparison of the Mg²⁺ block of NR3B-containing diheteromers with each of the NR1 splice variants. A. Current-voltage (IV) relationships for NR1–3b/NR2B (upper diagram, Glu/Gly-induced currents) and NR1–3b/NR3B (middle and lower diagrams for Glu/Gly- and Gly-induced currents, respectively) recorded between -150 mV and +50 mV. Recordings were performed in the presence of 300 μM glutamate (Glu) and/or 10 μM glycine (Gly) in the presence (dark grey traces) and absence (light grey traces) of 0.5 mM Mg²⁺. Traces represent averages from 4 experiments per combination (normalized to +20 mV). B. Comparison of the Mg²⁺ block of agonist-evoked current responses at -70 mV for each NR1 splice variant expressed alone, with NR2B, or with NR3B. Mean values ± SEM, n = 9–18 from 2–5 independent experiments per combination; *p < 0.05; **p < 0.01; ***p < 0.005 (Student's t-test). C. Exemplary potentiation by glutamate of glycine-induced NR1–3b/NR3B receptor currents in oocytes with high expression levels of Xen NR2B. Note that only the portion of current induced by additional glutamate is blocked by Mg²⁺. Current responses are mean values ± SEM normalized to the glycine-induced response (set to 100% and marked with #), n = 6. The inset shows a representative current trace from this batch recorded during sequential applications of agonists and Mg²⁺.