Mg2+ block of coexpressed mutant NMDAR subunits: mean values and current traces. A. Amino acid sequence of the pore loop regions of rodent NR1, NR2B, and NR3B. The native amino acids at the N and N+1 positions are boxed. B. Mean values (± SEM) of the Mg2+ block of N and N+1 site mutant NMDAR diheteromers. 0.5 mM Mg2+ was applied after activation of the receptor with 10 μM glycine (Gly) alone or in coapplication with 100 μM glutamate (Glu). Statistical significance was determined relative to the respective wild type combination. n = 5-27, *p < 0.05; **p < 0.01; ***p < 0.005. C. Representative current traces of the Mg2+ block of diheteromers featuring N and N+1 site mutant subunits. Agonists (conc. as in B) were applied for 60 s (long bar); Mg2+ was added for 20 s during the application (denoted by the short bar).