Figure 1. Whole-oocyte I-V relations of wild-type and mutant NMDA receptors. I-V relations were obtained in different oocytes expressing (wild-type) NR1-NR2A (A), NR1-NR2A(N+1S) (B), NR1(N0S)-NR2A (C) and NR1(N0Q)-NR2A (D) channels.

A-D,I-V relations were built using 2 s ramps from -150 to +100 mV applied in the presence and in the absence of 100 μM glutamate. Each graph shows two such I-V relations obtained either in the absence of external Mg²⁺, or in the presence of 100 μM external Mg²⁺. Note that in the four cases, the external Mg²⁺ only affects inward currents, and that the outward currents are not affected. E, the block by external Mg²⁺ is evaluated by the ratio (unblocked fraction, UF) of the current recorded in the presence of external Mg²⁺ over the current recorded in the absence of external Mg²⁺. F, the I-V relations of wild-type and mutant channels in the absence of external Mg²⁺ have been aligned by normalizing their current values to -100 mV. Continuous line, NR1-NR2A; ---, NR1- NR2A(N+1S); -. -. -, NR1(N0S)-NR2A; …., NR1(N0Q)-NR2A.