Comparative analysis of the pharmacology of GluR1 in complex with transmembrane AMPA receptor regulatory proteins γ2, γ3, γ4, and γ8

doi:10.1016/j.neuroscience.2007.12.047

Neuroscience

Volume 158, Issue 1, 12 January 2009, Pages 78-88

https://doi.org/10.1016/j.neuroscience.2007.12.047 Get rights and content

Abstract

AMPA receptors (AMPARs) mediate the majority of fast synaptic transmission in the CNS of vertebrates. They are believed to be associated with members of the transmembrane AMPA receptor regulatory protein (TARP) family. TARPs mediate the delivery of AMPA receptors to the plasma membrane and mediate their synaptic trafficking. Moreover, TARPs modulate essential electrophysiological properties of AMPA receptors. Here, we compare the influence of rat TARPs (γ2, γ3, γ4, and γ8) on pharmacological properties of rat GluR1(Q)flip. We show that agonist potencies are increased by all TARPs, but to individually different extents. On the other hand, all TARPs increase agonist potencies at the virtually non-desensitizing mutant GluR1-L479Y almost identically. Comparison of the influence of individual TARPs on relative agonist efficacies confirmed that the TARPs can be functionally subdivided into two subgroups, one consisting of γ2 and γ3 and one consisting of γ4 and γ8. Surprisingly, we found that TARPs convert certain AMPA receptor antagonists to agonists. The potency of one of these converted antagonists is dependent on the particular TARP. Moreover, TARPs (except γ4) reduce the ion channel block by the synthetic Joro spider toxin analog 1-naphthylacetyl spermine (NASP). In addition, TARPs increase the permeability of the receptor to calcium, indicating that TARPs directly modulate important ion pore properties. In summary, the data presented herein will illustrate and help to understand the previously unexpected complexities of modulation of AMPA receptor pharmacological properties by TARPs.

Section snippets

cRNA synthesis

The cDNA of the flip-isoformed rat GluR1(Q) receptor subunit as well as the cDNAs of the four rat TARPs were subcloned in the expression vector pSGEM that is optimized for expression in Xenopus laevis oocytes (Villmann et al., 1997). cRNA synthesis was performed as described earlier (Villmann et al., 1999). Briefly, template DNA was linearized with a suitable restriction enzyme. cRNA was synthesized from 1 μg of linearized DNA using an in vitro transcription kit (Fermentas, St. Leon-Rot,

Agonist potencies and efficacies reveal individual TARP-specific modulation of GluR1

It has previously been demonstrated that TARPs differentially increase the potency of glutamate at GluR1(Q)flip receptors, and that the extent of the observed increase is dependent on the associated TARP (Kott et al., 2007). Briefly, γ2 and γ3 increased the potency of glutamate most strongly; γ4 and γ8 also induced higher glutamate potencies, but less strongly than γ2 or γ3. We now observed that all TARPs increase glutamate potencies of the virtually non-desensitizing receptor mutant

Discussion

This study provides additional insight in the modulation of pharmacological properties of AMPA receptors by TARPs. An unexpected complexity becomes apparent as each TARP has a distinct impact on the extent of modulation. Moreover, we present evidence that TARPs convert certain AMPA receptor antagonists to agonists. In addition, we extended previous reports that the polyamine block and the calcium permeability of AMPA receptors are not only altered by γ2 (Soto et al., 2007), but also by γ3, γ4,

Conclusion

In summary, the study presented here demonstrates that TARPs modulate parameters of GluR1 receptor pharmacology such as ligand efficacies and potencies, block of the receptor by polyamines, and the permeability of the ion channel for calcium ions. We could also show that all TARPs convert certain AMPA receptor antagonists to partial agonists. Moreover, the extent of modulation of AMPA receptor pharmacology is strongly dependent on the contributing TARP, similar to what had been demonstrated

Acknowledgments

The authors would like to thank Björn Peters for expert oocyte preparations. M. Hollmann and S. Kott are supported by the Deutsche Forschungsgemeinschaft (DFG, HO 1118/11-1).

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Interacting PartnerComparative analysis of the pharmacology of GluR1 in complex with transmembrane AMPA receptor regulatory proteins γ2, γ3, γ4, and γ8

Abstract

Section snippets

cRNA synthesis

Agonist potencies and efficacies reveal individual TARP-specific modulation of GluR1

Discussion

Conclusion

Acknowledgments

Neuron

J Biol Chem

Neuron

Neuron

Neuron

J Biol Chem

Neuron

Biophys J

Neuron

J Biol Chem

Fractional calcium currents through recombinant GluR channels of the NMDA, AMPA and kainate receptor subtypes

J Physiol

Stargazin regulates synaptic targeting of AMPA receptors by two distinct mechanisms

Nature

Ca2+ permeability of unedited and edited versions of the kainate selective glutamate receptor GluR6

Proc Natl Acad Sci U S A

Impairment of AMPA receptor function in cerebellar granule cells of ataxic mutant mouse stargazer

J Neurosci

Structure of ionotropic glutamate receptors

Calcium permeability of KA-AMPA gated glutamate receptor channels depends on subunit composition

Science

Cloned glutamate receptors

Annu Rev Neurosci

Identification of a site in glutamate receptor subunits that controls calcium permeability

Science

Permeation of calcium through excitatory amino acid receptor channels in cultured rat hippocampal neurones

J Physiol

New transmembrane AMPA receptor regulatory protein isoform, gamma-7, differentially regulates AMPA receptors

J Neurosci

Mutation of a glutamate receptor motif reveals its role in gating and delta2 receptor channel properties

Nat Neurosci

Interacting Partner
Comparative analysis of the pharmacology of GluR1 in complex with transmembrane AMPA receptor regulatory proteins γ2, γ3, γ4, and γ8

Ca²⁺ permeability of unedited and edited versions of the kainate selective glutamate receptor GluR6