Zinc inhibition of rat NR1/NR2A N-methyl-D-aspartate receptors.
Zinc ions (Zn(2+)) are localized in presynaptic vesicles at glutamatergic synapses and released in an activity-dependent manner. Modulation of NMDA-type glutamate receptors by extracellular Zn(2+) may play an important role under physiological conditions and during pathologies such as ischaemia or seizure. Zn(2+) inhibits NMDA receptors containing the NR2A subunit with an IC(50) value in the low nanomolar concentration range. Here we investigate at the single-channel level the mechanism of high affinity Zn(2+) inhibition of recombinant NR1/NR2A receptors expressed in HEK293 cells. Zn(2+) 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 Zn(2+). Fitting the sequence of single-channel events with kinetic models suggests that the association of Zn(2+) 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 Zn(2+)-mediated inhibition of NMDA receptors primarily reflecting enhancement of proton inhibition.
Department of Pharmacology, Emory University School of Medicine, Rollins Research Center, Atlanta, GA 30322, USA.
Kevin
K
Erreger
Stephen F
SF
Traynelis
D000465:Algorithms; D000818:Animals; D002460:Cell Line; D004305:Dose-Response Relationship, Drug; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007668:Kidney / Q000166:cytology / Q000378:metabolism; D008954:Models, Biological; D018408:Patch-Clamp Techniques; D011522:Protons; D051381:Rats; D016194:Receptors, N-Methyl-D-Aspartate / Q000037:antagonists & inhibitors* / Q000187:drug effects / Q000378:metabolism; D014131:Trace Elements / Q000494:pharmacology*; D014162:Transfection; D015032:Zinc / Q000494:pharmacology*
C409466:NR1 NMDA receptor; C120997:NR2A NMDA receptor; D011522:Protons; D016194:Receptors, N-Methyl-D-Aspartate; D014131:Trace Elements; D015032:Zinc