Cations but not anions regulate the responsiveness of kainate receptors

Kainate-selective ionotropic glutamate receptors are unique among ligand-gated ion channels in their obligate requirement of external anions and cations for activation. Although it is established that the degree of kainate receptor (KAR) activation is shaped by the chemical nature of the agonist mol...

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Bibliographic Details
Published in:The Journal of neuroscience 2011-02, Vol.31 (6), p.2136-2144
Main Authors: Maclean, David M, Wong, Adrian Y C, Fay, Anne-Marie, Bowie, Derek
Format: Article
Language:English
Subjects:
Animals
Anions - metabolism
Anions - pharmacology
Biophysics
Cations - metabolism
Cations - pharmacology
Cell Line, Transformed
Chromates - pharmacology
Dose-Response Relationship, Drug
Electric Stimulation
Excitatory Amino Acid Agonists - pharmacology
GluK2 Kainate Receptor
Glutamic Acid - pharmacology
Green Fluorescent Proteins - genetics
Humans
Kainic Acid - pharmacology
Lysine - genetics
Lysine - metabolism
Membrane Potentials - drug effects
Membrane Potentials - genetics
Membrane Potentials - physiology
Models, Molecular
Mutation - genetics
Nitrates - pharmacology
Patch-Clamp Techniques
Protein Binding
Rats
Receptors, Kainic Acid - genetics
Receptors, Kainic Acid - metabolism
Sodium Iodide - pharmacology
Transfection
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Summary:Kainate-selective ionotropic glutamate receptors are unique among ligand-gated ion channels in their obligate requirement of external anions and cations for activation. Although it is established that the degree of kainate receptor (KAR) activation is shaped by the chemical nature of the agonist molecule, the possible complementary role of external ions has yet to be examined. Here we show that external cations but not anions regulate the responsiveness to a range of full and partial agonists acting on rat GluK2 receptors. This observation is unexpected as previous work has assumed anions and cations affect KARs in an identical manner through functionally coupled binding sites. However, our data demonstrate that anion- and cation-binding pockets behave discretely. We suggest cations uniquely regulate a pregating or flipping step that impacts the closed-cleft stability of the agonist-binding domain (ABD). This model departs from a previous proposal that KAR agonist efficacy is governed by the degree of closure elicited in the ABD by ligand binding. Our findings are, however, in line with recent studies on Cys-loop ligand-gated ion channels suggesting that the "flipping" mechanism has been conserved by structurally diverse ligand-gated ion channel families as a common means of regulating neurotransmitter behavior.
ISSN:0270-6474
1529-2401
DOI:10.1523/JNEUROSCI.4314-10.2011