title: Effects of divalent cations on slow unblock of native NMDA receptors in mouse neocortical pyramidal neurons.
abstract: The N-methyl-D-aspartate receptor (NMDAR) exhibits strong voltage-dependent block by extracellular Mg(2+) , which is relieved by sustained depolarization and glutamate binding, and which is central to the function of the NMDAR in synaptic plasticity. Rapid membrane depolarization during agonist application reveals a slow unblock of NMDARs, which has important functional implications, for example in the generation of NMDAR spikes, and in determining the narrow time window for spike-timing-dependent plasticity. However, its mechanism is still unclear. Here, we study unblock of divalent cations in native NMDARs in nucleated patches isolated from mouse cortical layer 2/3 pyramidal neurons. Comparing unblock kinetics of NMDARs in the presence of extracellular Mg(2+) or in nominally zero Mg(2+) , and with Mn(2+) or Co(2+) substituting for Mg(2+) , we found that the properties of slow unblock were determined by the identity of the blocking metal ion at the binding site, presumably by affecting the operation of a structural link to channel gating. The time course of slow unblock was not affected by zinc, or the zinc chelator TPEN [N,N,N',N'-tetrakis-(2-pyridylmethyl)-ethylenediamine], while the slower fraction of unblock was reduced by ifenprodil, an NR2B-selective antagonist. Slow unblock was only weakly temperature dependent, speeding up with rise in temperature with a Q(10) of ≈1.5. Finally, using action potential waveform voltage-clamp, we show that this slow relief from divalent cation block is a prominent feature in physiologically realistic patterns of changing membrane potential.
authors: Department of Physiology, Development and Neuroscience, University of Cambridge, Cambridge CB2 3EG, UK.
authors: Nam-Kyung
authors: NK
authors: Kim
authors: Hugh P C
authors: HP
authors: Robinson
mesh_terms: D000818:Animals; D002413:Cations, Divalent / Q000378:metabolism*; D002614:Chelating Agents / Q000378:metabolism; D005029:Ethylenediamines / Q000378:metabolism; D018691:Excitatory Amino Acid Antagonists / Q000378:metabolism; D005260:Female; D015640:Ion Channel Gating / Q000502:physiology; D008274:Magnesium / Q000378:metabolism; D008297:Male; D051379:Mice; D019579:Neocortex / Q000166:cytology*; D018408:Patch-Clamp Techniques; D010880:Piperidines / Q000378:metabolism; D017966:Pyramidal Cells / Q000166:cytology / Q000502:physiology*; D016194:Receptors, N-Methyl-D-Aspartate / Q000819:agonists / Q000037:antagonists & inhibitors* / Q000378:metabolism*; D015032:Zinc / Q000378:metabolism
chemical_list: D002413:Cations, Divalent; D002614:Chelating Agents; D005029:Ethylenediamines; D018691:Excitatory Amino Acid Antagonists; D010880:Piperidines; D016194:Receptors, N-Methyl-D-Aspartate; D008274:Magnesium; D015032:Zinc; C010739:ifenprodil; C044387:N,N,N',N'-tetrakis(2-pyridylmethyl)ethylenediamine