Rapid decay of averaged single-channel NMDA receptor activations recorded at low agonist concentration.
The NMDA class of glutamate receptors have the unique property of binding some agonists, including glutamate, for a very long period of time. One manifestation of this is that brief (1 ms) application of glutamate (1 mM) produces a slowly decaying current, the major component of which has a time constant of approximately 200 ms. Application of glutamate at low concentrations allows identification of groups ('superclusters') of openings in the data record that probably correspond to a single period during which one or more molecules of glutamate are bound to the receptor, i.e. a single activation of the channel. The length of such superclusters is long on average (74 ms); the longest component of the distribution has a duration of approximately 300 ms, and comprises about 25% of the area. However, aligning many superclusters to obtain an average current reveals that the decay is mainly fast; the major component has a time constant of around only 5 ms. It is shown that incorporation of a distribution of first latencies (from the time of the jump to the first opening) can explain at least part of this discrepancy.
Edmonds
B
B
Department of Pharmacology, University College London, U.K.
Colquhoun
D
D
D000818:Animals; D005971:Glutamates / Q000494:pharmacology*; D018698:Glutamic Acid; D005998:Glycine / Q000494:pharmacology*; D006624:Hippocampus / Q000502:physiology*; D066298:In Vitro Techniques; D007473:Ion Channels / Q000187:drug effects / Q000502:physiology*; D007700:Kinetics; D008433:Mathematics; D008564:Membrane Potentials; D008959:Models, Neurological; D051381:Rats; D017470:Receptors, Glutamate / Q000187:drug effects / Q000502:physiology*; D016194:Receptors, N-Methyl-D-Aspartate / Q000187:drug effects / Q000502:physiology*
D005971:Glutamates; D007473:Ion Channels; D017470:Receptors, Glutamate; D016194:Receptors, N-Methyl-D-Aspartate; D018698:Glutamic Acid; D005998:Glycine