Figure 2. Suppression of dNMDAR Mg²⁺ Block in Neurons from Transgenic Pupae Overexpressing dNR1(N631Q).

(A) Schematic diagram of dNR1 and amino acid sequence comparisons of the TM2 domains of Drosophila (dNR1 and dNR2), mouse (NR1, NR2A, and NR2C), and C. elegans (NMR1 and NMR2) NMDAR subunits. The white circle (upper) and shadowed box (lower) indicate the Mg²⁺ block site in the TM2 domain.

(B) Current-voltage (I-V) curves generated from neurons from elav/dNR1(wt) (n = 6) and elav/dNR1(N631Q) pupae (n = 6). Currents elicited by 100 μM NMDA were normalized to peak responses at +50 mV. Due to Mg²⁺ block, all examined neurons from elav/dNR1(wt) displayed a typical J-shaped I-V relation in the presence of 20 mM extracelluar Mg²⁺.

(C) (Left) I-V relationships in high Na⁺ (open circle) and high Ca²⁺ (closed circle) extracellular solutions for elav/dNR1(wt) and elav/dNR1(N631Q) neurons. I-V relationships in each extracellular solution were recorded from the same neuron after confirming the presence [for elav/dNR1(wt)] or absence [for elav/dNR1(N631Q)] of Mg²⁺ block. (Right) Reversal potentials in high Na⁺ extracellular solution (V_rev,Na) and in high Ca²⁺ extracellular solution (V_rev,Ca) were measured from the left panel, and relative Ca²⁺ permeabilities (P_Ca/P_Na) were calculated using the Goldman-Hodgkin-Katz (GHK) equation.

See also Figures S2 and S3.