1722243

Desensitization and resensitization rates of glutamate-activated channels may regulate motoneuron excitability.

Article date: 1991/10/1

PubMed ID: 1722243

Journal name: Journal of neurophysiology (ISSN: 0022-3077)

ABSTRACT

1. Single-channel properties of desensitizing glutamate-activated channels were analyzed in outside-out patch-clamp recordings from a motoneuron-enriched cell fraction from embryonic chick. A piezo-driven device was used to achieve fast solution exchange at the electrode tip, resulting in maximum activation within 2 ms. 2. Quisqualate/AMPA receptors, with a 13-pS conductance, desensitized rapidly; the desensitization rate depended on agonist concentration but not on membrane potential. When quisqualate was applied slowly, the quisqualate-activated channels desensitized without prior channel opening, indicating desensitization from the closed state. After a 10-ms refractory period, resensitization of all channels required up to 300 ms; resensitization rate did not depend on the duration of the preceding quisqualate application. 3. At agonist concentrations less than or equal to 1 mM, kainate receptors, with a 20-pS conductance, did not desensitize. At kainate concentrations greater than or equal to 1 mM, though, kainate receptors desensitized to a low steady-state conductance within approximately 200 ms. Resensitization of all channels required as long as 3 s, which could render kainate receptors inexcitable during high-frequency activation. 4. Desensitization rates of whole-cell currents were similar to those observed in outside-out mode. Glutamate- and quisqualate-activated responses were similar, suggesting that the rapidly desensitizing quisqualate-sensitive receptor type may dominate the kinetics of whole-cell excitatory postsynaptic currents (EPSCs) in this preparation. 5. It may be concluded that the efficacy of glutamate-mediated synaptic transmission is modulated by differences in the rates of desensitization and resensitization.

Author List: Smith D O, Franke C, Rosenheimer J L, Zufall F, Hatt H

Publication Types: Journal Article; Research Support, Non-U.S. Gov't; Research Support, U.S. Gov't, P.H.S.

Substances mentioned in the article: Glutamates; Ion Channels; Quinoxalines; Ibotenic Acid; 6-Cyano-7-nitroquinoxaline-2,3-dione; alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid; Quisqualic Acid; Kainic Acid;

Mesh terms: 6-Cyano-7-nitroquinoxaline-2,3-dione; Animals; Cell Membrane/drug effects; Chick Embryo; Electrophysiology; Glutamates/pharmacology; Ibotenic Acid/analogs & derivatives; Ion Channels/drug effects; Kainic Acid/pharmacology; Motor Neurons/physiology; Quinoxalines/pharmacology; Quisqualic Acid/pharmacology; Synaptic Transmission/drug effects; alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid;

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