NMDA receptor gating reactions (A) Rate constants (s^-1) were optimized with the illustrated 5C1O kinetic scheme from fits to single-channel data and are given as the rounded average for each data set.

<p>*, indicates significant changes (red, faster; blue, slower) relative to N1/2A receptors (p<0.05, Student’s <i>t</i>-test).</p

Single channel activity of NMDA receptors with side-chain truncation in the LBD cleft.

<p>(<b>A</b>) Currents were recorded from attached patches of HEK293 cells expressing N1^KE/N2A^KN, N1K/A/2A, N1/2A^K/A, or N1K/A/2A^K/A receptors (<b>B</b>) Dwell time histograms for closed and open events recorded from one N1/N2A channel (799,601 events). Thin lines represent exponential components; insets give the time constants (τ) and relative areas (<i>a</i>) for these components. (C) Summary of changes in time constants (top) and areas (bottom) for closed and open components for the mutations examined. *, indicates significant changes relative to N1/2A receptors (p<0.05, Student’s <i>t</i>-test).</p

Single-channel currents of NMDA receptors with isosteric substitutions in the LBD pocket (A) Currents were recorded from attached patches on HEK293 cells expressing N1^K/M/2A or N1/2A^N/L receptors.

<p>(<b>B</b>) Summary of changes in closed time constants (<i>left</i>) and areas (<i>right</i>). *, indicates significant changes relative to N1/2A receptors (p<0.05, Student’s <i>t</i>-test).</p

Putative cleft-spanning interactions in the LBD of GluN subunits.

<p><i>Top</i>, proposed arrangements of the LBDs of glycine-bound GluN1(left, PDB 1PB7) and glutamate-bound GluN2A (<i>right</i>, PDB 2A5S) illustrate the position and cross-cleft distance of K483 and E712 (2.9 Å), and K487 and N687 side chains (2.9 Å), respectively. <i>Bottom</i>, PyMol representations of the substitutions examined in this study showing cross-cleft distances: <i>right</i>, N1^K/A 7.0 Å and N1^K/M 3.1 Å; <i>left</i>, N2^K/A 5.5 Å and N2^N/L 2.6 Å. </p

Macroscopic NMDA receptor currents.

<p>(A) Responses to long pulses of glutamate (5 s, 1 mM) were simulated with the models in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0080953#pone-0080953-g004" target="_blank">Figure 4</a> (<i>left</i>) or were recorded as whole-cell currents from HEK293 cells expressing the indicated receptors (<i>right</i>). (<b>B</b>) Synaptic-like responses were simulated with the models in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0080953#pone-0080953-g004" target="_blank">Figure 4</a>. (<b>C</b>) Macroscopic responses were recorded from outside-out patches pulled from HEK293 cells expressing WT or N1/2A^N/L receptors in response to brief exposure to glutamate (arrow: 10 ms, 1 mM); experimental traces were normalized to peak and overlaid for comparison. </p