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J Physiol Volume 586, Number 3, 763-778, February 1, 2008 DOI: 10.1113/jphysiol.2007.143941
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NEUROSCIENCE

Zinc inhibition of rat NR1/NR2A N-methyl-D-aspartate receptors

 Kevin Erreger1 and Stephen F. Traynelis1

1 Department of Pharmacology, Emory University School of Medicine, Rollins Research Center, Atlanta, GA 30322, USA

Zinc ions (Zn2+) are localized in presynaptic vesicles at glutamatergic synapses and released in an activity-dependent manner. Modulation of NMDA-type glutamate receptors by extracellular Zn2+ may play an important role under physiological conditions and during pathologies such as ischaemia or seizure. Zn2+ inhibits NMDA receptors containing the NR2A subunit with an IC50 value in the low nanomolar concentration range. Here we investigate at the single-channel level the mechanism of high affinity Zn2+ inhibition of recombinant NR1/NR2A receptors expressed in HEK293 cells. Zn2+ reversibly decreases the mean single-channel open duration and channel open probability determined in excised outside-out patches, but has no effect on single-channel current amplitude. A parallel series of experiments demonstrates that lowering extracellular pH (increasing proton concentration) has a similar effect on NR1/NR2A single-channel properties as Zn2+. Fitting the sequence of single-channel events with kinetic models suggests that the association of Zn2+ with its binding site enhances proton binding. Modelling further suggests that protonated channels are capable of opening but with a lower open probability than unprotonated channels. These data and analyses are consistent with Zn2+-mediated inhibition of NMDA receptors primarily reflecting enhancement of proton inhibition.

(Received 27 August 2007; accepted after revision 23 November 2007; first published online 29 November 2007)
Corresponding author S. F. Traynelis: Department of Pharmacology, Emory University School of Medicine, Rollins Research Center, Atlanta, GA 30322, USA.  Email: strayne{at}emory.edu

This paper has online supplemental material.






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