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. 2011 Aug;138(2):179–194. doi: 10.1085/jgp.201110623

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© 2011 Talukder and Wollmuth

This article is distributed under the terms of an Attribution–Noncommercial–Share Alike–No Mirror Sites license for the first six months after the publication date (see http://www.rupress.org/terms). After six months it is available under a Creative Commons License (Attribution–Noncommercial–Share Alike 3.0 Unported license, as described at http://creativecommons.org/licenses/by-nc-sa/3.0/).

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Figure 3. — A subset of cell surface NMDA receptors with double-cysteine–substituted GluN1 or GluN2A is resistant to pore block by MK801. To optimize current amplitudes in these experiments, we injected WT GluN1/GluN2A at 1 ng/µL and GluN1(C,C)/GluN2A and GluN1/GluN2A(C,C) at 10 ng/µL into Xenopus oocytes. (A and B) Example recordings depicting steady-state MK801 inhibition of NMDA receptor–mediated macroscopic currents. MK801 (open bar; 1–2 µM; 1 min), applied in the presence of agonists (thin lines), inhibited current amplitudes for GluN1/GluN2A (A), GluN1(C,C)/GluN2A (B), and GluN1/GluN2A(C,C) (not depicted) receptors. Subsequent application of DTT (filled bar) in the channel closed state (as in Fig. 2 C) significantly potentiated current amplitudes of the double-cysteine–substituted receptor (B) relative to WT GluN1/GluN2A (A). (C) Mean percent change (±SEM; n ≥ 4) in current amplitudes either immediately after MK801 (MK801) or after MK801, but with an intervening treatment by DTT in the presence of antagonists (DTT) or antagonists alone (antag.). For DTT and antagonist-alone treatments, percent change was calculated relative to the current amplitudes preceding these treatments but after MK801 block. Negative and positive values represent current inhibition and potentiation, respectively. Filled bars indicate values significantly different from those of WT GluN1/GluN2A receptors (P < 0.05). (D and E) 25 nM MK801 was applied in the presence of agonists until steady-state current inhibition was reached. (E, right) For GluN1(C,C)/GluN2A, MK801 was also applied to DTT-potentiated currents. Single- (gray dashed lines) and biexponential (green dashed lines) fits to MK801-mediated current inhibition are shown, as well as the residuals (I_res) to the two fits. For GluN1/GluN2A, single-exponential fits were sufficient to describe the time course of MK801-mediated current inhibition, whereas for GluN1(C,C)/GluN2A, biexponential fits were required, as determined by qualitative minimization of I_res. (F) Normalized MK801-mediated inhibition of currents with the overlayed best fits (dashed lines). (G) Averaged time constants of single-exponential fits (τ), as well as the fast (τ_f) and slow (τ_s) components of the biexponential fits (±SEM) to MK801-mediated current inhibition. (H) Averaged percentage of area (±SEM) occupied by each component of the exponential fits.