GluR3 Flip and Flop:  Differences in Channel Opening Kinetics

Pei, Weimin; Huang, Zhen; Niu, Li

doi:10.1021/bi062213s

Cited by 47 publications

(91 citation statements)

References 65 publications

(116 reference statements)

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“…Indeed, this hypothesis is consistent with previous observations that desensitization is agonist-promoted (32) and that the L497Y mutant channels can desensitize, albeit very slowly and only at very high concentrations of ligand, as observed by us and others (6,9). Moreover, that the rate of the channel closing controls the rate of desensitization is supported by our results with the GluR3 receptors in that the k cl of the GluR3 flop variant is ϳ4-fold larger than that of the flip isoform, and the flop isoform desensitizes ϳ4-fold faster than the flip isoform (29). On the other hand, for the flip and flop isoforms of GluR1, the k cl of both isoforms is identical, within experimental errors, and as expected, the channel desensitization rate constant is also no different.…”

Section: Implications Based On the Kinetic Constants And Free Energysupporting

confidence: 87%

“…For instance, the k cl of the L497Y mutant is smaller than that of the wild type, suggesting that this structural modification lowers the energy level of the open channel state by stabilizing it. In contrast, our study of the alternatively spliced variants of GluR3 or GluR3 flip and GluR3 flop shows that the flop isoform has a larger k cl than the flip isoform, presumably reflecting that the flop isoform destabilizes the channel-open state (29). By the same prediction, any mutation or change of structure (whether it is located in the dimer interface, such as the mutation in GluR2, but is equivalent to the L497Y in GluR1 (6), or elsewhere but nevertheless stabilizes the open channel state) would slow the rate of channel closing.…”

Section: Implications Based On the Kinetic Constants And Free Energycontrasting

confidence: 77%

“…By this notion, desensitization begins in parallel to the channel-opening reaction once glutamate is bound but proceeds from the closed channel state and with a slower rate. In fact, in this and all other studies of AMPA receptor channels, we have found that the rate of channel closing is markedly faster than the rate of the channel desensitization (11,13,14,29). The common "species" that links the two reactions is the closed channel state, although it is unclear which closed channel form(s) enters the desensitization pathway.…”

Section: Implications Based On the Kinetic Constants And Free Energymentioning

confidence: 47%

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Receptor Occupancy and Channel-opening Kinetics

Pei

Ritz

McCarthy

et al. 2007

Journal of Biological Chemistry

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AMPA glutamate ion channels are tetrameric receptors in which activation to form the open channel depends on the binding of possibly multiple glutamate molecules. However, it is unclear whether AMPA receptors bound with a different number of glutamate molecules (i.e. one being the minimal and four being the maximal number of glutamate molecules) open the channels with different kinetic constants. Using a laser pulse photolysis technique that provides microsecond time resolution, we investigated the channel-opening kinetic mechanism of a nondesensitizing AMPA receptor, i.e. GluR1Q flip L497Y or a leucine-to-tyrosine substitution mutant, in the entire range of glutamate concentrations to ensure receptor saturation. We found that the minimal number of glutamate molecules required to bind to the receptor and to open the channel is two (or n ‫؍‬ 2), and that the entire channel-opening kinetics can be adequately described by just one channel-opening rate constant, k op , which correlates to n ‫؍‬ 2. This result suggests that higher receptor occupancy (n ‫؍‬ The ␣-amino-3-hydroxy-5-methyl-4-isoxazole-propionic acid (AMPA) 3 glutamate receptors are ligand-gated ion channels that are activated by binding of neurotransmitter glutamate (1, 2). An AMPA receptor is a tetrameric assembly with each subunit containing a glutamate binding site. The receptor can adopt multiple conductance levels, especially at high receptor occupancy, as observed in the single-channel records of wild-type and mutant recombinant receptors (3, 4) as well as native AMPA receptors (5). However, it remains unclear whether receptor occupancy plays a significant role in determining the kinetic constants for an ensemble rate process of channel opening as a function of glutamate concentration. The ensemble rate process is manifested in a whole-cell current response to the binding of glutamate in vitro and best represents the glutamatergic synaptic activity in vivo, such as excitatory postsynaptic current. Therefore, determining the number of glutamate molecules bound to a receptor or the percentage of the receptor occupancy pertinent to the rate of the channel opening is a basic question to be answered for understanding the function of AMPA receptors.To address this question, we investigated the channel-opening kinetics for a GluR1 AMPA receptor channel carrying a substitution of leucine (L) to tyrosine (Y) or L497Y. The discovery of this point mutation by Stern-Bach et al. (3) was a significant event in understanding the structure and function relationship of AMPA receptors in that (a) phenomenologically, the single leucine-to-tyrosine substitution renders the homomeric receptor channels virtually non-desensitizing (3), and (b) the phenotypic effect of this mutation is conserved at equivalent positions in all AMPA receptor subunits, i.e. GluR1-4 (6 -8). Furthermore, this mutation is thought to have no effect on either the main conductance level or the channel opening probability (3,7,9). From a crystallographic study, Sun et al. (6) revealed that this ...

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Section: Implications Based On the Kinetic Constants And Free Energysupporting

confidence: 87%

Section: Implications Based On the Kinetic Constants And Free Energycontrasting

confidence: 77%

Section: Implications Based On the Kinetic Constants And Free Energymentioning

confidence: 47%

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Receptor Occupancy and Channel-opening Kinetics

Pei

Ritz

McCarthy

et al. 2007

Journal of Biological Chemistry

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“…AMPAR flip subunitcontaining receptors are more efficiently activated by glutamate and they desensitize with slower kinetics (Mosbacher et al, 1994;Sommer et al, 1990). GluA3(Q)-flip receptors, for example, recover more quickly from desensitization and display 4-fold longer channel open times than GluA3(Q)-flop (Pei et al, 2007;Pei et al, 2009).…”

Section: The Importance Of Flip and (Q) Variantsmentioning

confidence: 99%

Cell class-specific regulation of neocortical dendrite and spine growth by AMPA receptor splice and editing variants

et al. 2011

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SUMMARYGlutamatergic transmission converging on calcium signaling plays a key role in dendritic differentiation. In early development, AMPA receptor (AMPAR) transcripts are extensively spliced and edited to generate subunits that differ in their biophysical properties. Whether these subunits have specific roles in the context of structural differentiation is unclear. We have investigated the role of nine GluA variants and revealed a correlation between the expression of flip variants and the period of major dendritic growth. In interneurons, only GluA1(Q)-flip increased dendritic length and branching. In pyramidal cells, GluA2(Q)-flop, GluA2(Q)-flip, GluA3(Q)-flip and calcium-impermeable GluA2(R)-flip promoted dendritic growth, suggesting that flip variants with slower desensitization kinetics are more important than receptors with elevated calcium permeability. Imaging revealed significantly higher calcium signals in pyramidal cells transfected with GluA2(R)-flip as compared with GluA2(R)-flop, suggesting a contribution of voltage-activated calcium channels. Indeed, dendritic growth induced by GluA2(R)-flip in pyramidal cells was prevented by blocking NMDA receptors (NMDARs) or voltage-gated calcium channels (VGCCs), suggesting that they act downstream of AMPARs. Intriguingly, the action of GluA1(Q)-flip in interneurons was also dependent on NMDARs and VGCCs. Cell class-specific effects were not observed for spine formation, as GluA2(Q)-flip and GluA2(Q)-flop increased spine density in pyramidal cells as well as in interneurons. The results suggest that AMPAR variants expressed early in development are important determinants for activity-dependent dendritic growth in a cell type-specific and cell compartment-specific manner.

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“…2D) cannot be explained by passive cable properties associated with possible lack of space clamp and require an alternative explanation. While one possibility is postsynaptic receptor diversity (Bonsacquet et al 2006;Harms et al 2014;Mayer 2011;Pei et al 2007), another is that transmitter accumulation in the confined calyceal cleft prolongs EPSCs arising at specific synaptic sites (see Fig. 4 and discussion below) (Sadeghi et al 2014).…”

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confidence: 99%

The quantal component of synaptic transmission from sensory hair cells to the vestibular calyx

Highstein

Mann

Rabbitt

2015

Journal of Neurophysiology

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Highstein SM, Mann MA, Holstein GR, Rabbitt RD. The quantal component of synaptic transmission from sensory hair cells to the vestibular calyx. J Neurophysiol 113: 3827-3835, 2015. First published April 15, 2015 doi:10.1152/jn.00055.2015.-Spontaneous and stimulus-evoked excitatory postsynaptic currents (EPSCs) were recorded in calyx nerve terminals from the turtle vestibular lagena to quantify key attributes of quantal transmission at this synapse. On average, EPSC events had a magnitude of ϳ42 pA, a rise time constant of 0 ϳ229 s, decayed to baseline with a time constant of R ϳ690 s, and carried ϳ46 fC of charge. Individual EPSCs varied in magnitude and decay time constant. Variability in the EPSC decay time constant was hair cell dependent and due in part to a slow protraction of the EPSC in some cases. Variability in EPSC size was well described by an integer summation of unitary quanta, with each quanta of glutamate gating a unitary postsynaptic current of ϳ23 pA. The unitary charge was ϳ26 fC for EPSCs with a simple exponential decay and increased to ϳ48 fC for EPSCs exhibiting a slow protraction. The EPSC magnitude and the number of simultaneous unitary quanta within each event increased with presynaptic stimulus intensity. During tonic hair cell depolarization, both the EPSC magnitude and event rate exhibited adaptive run down over time. Present data from a reptilian calyx are remarkably similar to noncalyceal vestibular synaptic terminals in diverse species, indicating that the skewed EPSC size distribution and multiquantal release might be an ancestral property of inner ear ribbon synapses. auditory; vestibular; synapse; unitary quanta INNER EAR VESTIBULAR OTOLITH organs including the saccule, utricle, and in some species the lagena are broad-band sensors that encode low-frequency changes in gravito-inertial acceleration or static tilt relative to gravity (Goldberg 2012) and encode high-frequency sound or vibration (Curthoys et al.

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GluR3 Flip and Flop: Differences in Channel Opening Kinetics

Cited by 47 publications

References 65 publications

Receptor Occupancy and Channel-opening Kinetics

Receptor Occupancy and Channel-opening Kinetics

Cell class-specific regulation of neocortical dendrite and spine growth by AMPA receptor splice and editing variants

The quantal component of synaptic transmission from sensory hair cells to the vestibular calyx

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