Positive Allosteric Modulators of AMPA Receptors Reduce Proton-Induced Receptor Desensitization in Rat Hippocampal Neurons

2001 ◽  
Vol 85 (5) ◽  
pp. 2030-2038 ◽  
Author(s):  
Saobo Lei ◽  
Beverley A. Orser ◽  
Gregory R. L. Thatcher ◽  
James N. Reynolds ◽  
John F. MacDonald
Keyword(s):  
Ampa Receptor ◽  
Ampa Receptors ◽  
Hippocampal Neurons ◽  
Organic Nitrate ◽  
Receptor Desensitization ◽  
Open Probability ◽  
Ca1 Neurons ◽  
Hippocampal Ca1 ◽  
Rate Of Recovery ◽  
Kinetics Of

Whole-cell or outside-out patch recordings were used to investigate the effects of protons and positive modulators of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors on the desensitization of glutamate-evoked AMPA receptor currents in isolated hippocampal CA1 neurons. Protons inhibited glutamate-evoked currents (IC50 of 6.2 pH units) but also enhanced the apparent rate and extent of AMPA receptor desensitization. The proton-induced enhancement of desensitization could not be attributed to a reduction in the rate of recovery from desensitization or to a change in the kinetics of deactivation. Non-stationary variance analysis indicated that protons reduced maximum open probability without changing the conductance of AMPA channels. The positive modulators of AMPA receptor desensitization, cyclothiazide and GT-21-005 (an organic nitrate), reduced the proton sensitivity of AMPA receptor desensitization, which suggests that they interact with protons to diminish desensitization. In contrast, the effects of wheat germ agglutinin and aniracetam on AMPA receptor desensitization were independent of pH. These results demonstrate that a reduction in the proton sensitivity of receptor desensitization contributes to the mechanism of action of some positive modulators of AMPA receptors.

AMPA receptor heterogeneity in rat hippocampal neurons revealed by differential sensitivity to cyclothiazide

1996 ◽  
Vol 75 (6) ◽  
pp. 2322-2333 ◽  
Author(s):  
M. W. Fleck ◽  
R. Bahring ◽  
D. K. Patneau ◽  
M. L. Mayer
Keyword(s):  
Ampa Receptor ◽  
Ampa Receptors ◽  
Hippocampal Neurons ◽  
Splice Variants ◽  
Differential Sensitivity ◽  
Stratum Radiatum ◽  
Receptor Subtypes ◽  
Receptor Desensitization ◽  
B Subunits ◽  
Kinetics Of

1. The kinetics of onset of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor desensitization by glutamate, and the extent of attenuation of AMPA receptor desensitization by cyclothiazide, showed pronounced cell-to-cell variation in cultures of rat hippocampal neurons. Cultures prepared from area CA1 stratum radiatum tended to show weaker modulation by cyclothiazide than cultures prepared from the whole hippocampus. 2. Kinetic analysis of concentration jump responses to glutamate revealed multiple populations of receptors with fast (approximately 400 ms), intermediate (approximately 2-4 s), and slow (> 20 s) time constants for recovery from modulation by cyclothiazide. The amplitudes of these components varied widely between cells, suggesting the existence of at least three populations of AMPA receptor subtypes, the relative density of which varied from cell to cell. 3. The complex patterns of sensitivity to cyclothiazide seen in hippocampal neurons could be reconstituted by assembly of recombinant AMPA receptor subunits generated from cDNAs encoding the flip (i) and flop (o) splice variants of the GluR-A and GluR-B subunits. Recovery from modulation by cyclothiazide was slower for GluR-AiBi and GluR-AoBi than for GluR-AiBo and GluR-AoBo. 4. Coexpression of the flip and flop splice variants of GluR-A, in the absence of GluR-B, revealed that heteromeric AMPA receptors with intermediate sensitivity to cyclothiazide, similar to responses observed for the combinations GluR-AoBi or GluR-AiBo, could be generated independently of the presence of the GluR-B subunit. However, recovery from modulation by cyclothiazide was twofold slower for GluR-AiBi than for homomeric GluR-Ai, indicating that the GluR-A and GluR-B subunits are not functionally equivalent in controlling sensitivity to cyclothiazide. 5. These results demonstrate that AMPA receptors expressed in hippocampal neurons are assembled in a variety of subunit and splice variant combinations that might serve as a mechanism to fine-tune the kinetics of synaptic transmission.

Kinetics of Muscarinic Reduction of I sAHP in Hippocampal Neurons: Effects of Acetylcholinesterase Inhibitors

1997 ◽  
Vol 78 (6) ◽  
pp. 2999-3007 ◽  
Author(s):  
Y. Zhang ◽  
P. L. Carlen ◽  
L. Zhang
Keyword(s):  
Hippocampal Neurons ◽  
Brain Slices ◽  
Acetylcholinesterase Inhibitors ◽  
Time Interval ◽  
Ca1 Neurons ◽  
Ache Inhibitors ◽  
Afferent Stimulus ◽  
Hippocampal Ca1 Neurons ◽  
Hippocampal Ca1 ◽  
Kinetics Of

Zhang, Y., P. L. Carlen, and L. Zhang. Kinetics of muscarinic reduction of I sAHP in hippocampal neurons: effects of acetylcholinesterase inhibitors. J. Neurophysiol. 78: 2999–3007, 1997. The present experiments were designed to elucidate the time frame in which an evoked cholinergic impulse decreases the Ca2+-dependent K+ current ( I sAHP) in hippocampal CA1 neurons, and to determine to what extent acetylcholinesterase (AChE) inhibitors enhance the efficacy of the cholinergic impulse. Whole cell voltage-clamp recordings were performed on hippocampal CA1 neurons of rat brain slices and I sAHPs were evoked by constant depolarizing pulses. Cholinergic afferent fibers in stratum oriens were stimulated electrically and the time interval between the afferent stimulus and the depolarizing pulse was varied from 1 to 30 s. In slices perfused with the standard external medium, the afferent stimulus caused a profound decrease in the following I sAHP only when the stimulus preceded the depolarizing pulse by 1–2 s. The stimulus was without effects on the I sAHP when applied ≥5s before the depolarizing pulse. The effects of the afferent stimulus were greatly enhanced in CA1 neurons exposed to the catalytic AChE inhibitors neostigmine, physostigmine, or 9-amino-1,2,3,4-tetrahydro-acridine. A substantial decrease in the I sAHP was observed even when the stimulus preceded the depolarizing pulse by ≥30 s. However applications of peripheral site AChE inhibitors decamethonium and propidium caused only minor or no enhancement of the I sAHP reduction after the afferent stimulus. We suggest in physiological conditions that muscarinic modulation of ionic conductances of CNS neurons has a limited time course after a cholinergic impulse and that the modulation is greatly enhanced and prolonged when catalytic activities of AChEs are suppressed pharmacologically.

Modulation of AMPA receptors by a novel organic nitrate

2001 ◽  
Vol 79 (5) ◽  
pp. 422-429 ◽  
Author(s):  
Samuel Toong ◽  
Zhi-Gang Xiong ◽  
Sergei I Zavorin ◽  
Donglin Bai ◽  
B A Orser ◽  
...  
Keyword(s):  
Steady State ◽  
Ampa Receptors ◽  
Hippocampal Neurons ◽  
Organic Nitrate ◽  
Organic Nitrates ◽  
Current Response ◽  
Maximal Increase ◽  
Steady State Current ◽  
Rate Of Recovery ◽  
Cultured Hippocampal Neurons

Positive modulators of α-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) channels reduce desensitization and alter their gating kinetics. We have discovered a novel compound nitric oxide-mimetic that similarly modulates the AMPA receptor by reducing desensitization. This, designated GT-005, belongs to the organic nitrate family that includes the nitrovasodilator nitroglycerine. In acutely isolated hippocampal neurons, GT-005 enhanced kainate (100 µM)-evoked currents with an EC50 of 1.7 ± 0.2 mM and a 176 ± 10% maximal increase in the steady-state current response. Similar results were found in cultured hippocampal neurons (EC50 of 1.3 ± 0.2 mM and a maximal 83 ± 14% increase in the steady-state current response). GT-005 reduced the desensitization of glutamate-evoked currents and slowed the onset of desensitization. This compound also increased the rate of recovery from the desensitized state. With respect to alteration of the excitatory synaptic transmission, GT-005 delayed the decay and increased the frequency of spontaneous miniature excitatory postsynaptic currents (mepsc) recorded in cultured hippocampal neurons.Key words: AMPA receptors, desensitization, organic nitrates.

scholarly journals Control of AMPA receptor activity by the extracellular loops of auxiliary proteins

eLife ◽  
2017 ◽  
Vol 6 ◽  
Author(s):  
Irene Riva ◽  
Clarissa Eibl ◽  
Rudolf Volkmer ◽  
Anna L Carbone ◽  
Andrew JR Plested
Keyword(s):  
Ampa Receptor ◽  
Ampa Receptors ◽  
De Novo ◽  
Dominant Role ◽  
Mammalian Brain ◽  
Binding Assays ◽  
Receptor Kinetics ◽  
Receptor Complexes ◽  
Extracellular Loops ◽  
Kinetics Of

At synapses throughout the mammalian brain, AMPA receptors form complexes with auxiliary proteins, including TARPs. However, how TARPs modulate AMPA receptor gating remains poorly understood. We built structural models of TARP-AMPA receptor complexes for TARPs γ2 and γ8, combining recent structural studies and de novo structure predictions. These models, combined with peptide binding assays, provide evidence for multiple interactions between GluA2 and variable extracellular loops of TARPs. Substitutions and deletions of these loops had surprisingly rich effects on the kinetics of glutamate-activated currents, without any effect on assembly. Critically, by altering the two interacting loops of γ2 and γ8, we could entirely remove all allosteric modulation of GluA2, without affecting formation of AMPA receptor-TARP complexes. Likewise, substitutions in the linker domains of GluA2 completely removed any effect of γ2 on receptor kinetics, indicating a dominant role for this previously overlooked site proximal to the AMPA receptor channel gate.

Theta-Frequency Resonance in Hippocampal CA1 Neurons In Vitro Demonstrated by Sinusoidal Current Injection

1998 ◽  
Vol 79 (3) ◽  
pp. 1592-1596 ◽  
Author(s):  
L. Stan Leung ◽  
Hui-Wen Yu
Keyword(s):  
Resonant Frequency ◽  
Hippocampal Neurons ◽  
Ca1 Neurons ◽  
Frequency Resonance ◽  
Hippocampal Ca1 Neurons ◽  
Hippocampal Ca1 ◽  
Theta Frequency ◽  
Sinusoidal Current ◽  
Sinusoidal Currents

Leung, L. Stan and Hui-Wen Yu. Theta-frequency resonance in hippocampal CA1 neurons in vitro demonstrated by sinusoidal current injection. J. Neurophysiol. 79: 1592–1596, 1998. Sinusoidal currents of various frequencies were injected into hippocampal CA1 neurons in vitro, and the membrane potential responses were analyzed by cross power spectral analysis. Sinusoidal currents induced a maximal (resonant) response at a theta frequency (3–10 Hz) in slightly depolarized neurons. As predicted by linear systems theory, the resonant frequency was about the same as the natural (spontaneous) oscillation frequency. However, in some cases, the resonant frequency was higher than the spontaneous oscillation frequency, or resonance was found in the absence of spontaneous oscillations. The sharpness of the resonance ( Q), measured by the peak frequency divided by the half-peak power bandwidth, increased from a mean of 0.44 at rest to 0.83 during a mean depolarization of 6.5 mV. The phase of the driven oscillations changed most rapidly near the resonant frequency, and it shifted about 90° over the half-peak bandwidth of 8.4 Hz. Similar results were found using a sinusoidal function of slowly changing frequency as the input. Sinusoidal currents of peak-to-peak intensity of >100 pA may evoke nonlinear responses characterized by second and higher harmonics. The theta-frequency resonance in hippocampal neurons in vitro suggests that the same voltage-dependent phenomenon may be important in enhancing a theta-frequency response when hippocampal neurons are driven by medial septal or other inputs in vivo.

Gadolinium Reduces AMPA Receptor Desensitization and Deactivation in Hippocampal Neurons

2001 ◽  
Vol 86 (1) ◽  
pp. 173-182 ◽  
Author(s):  
Saobo Lei ◽  
John F. MacDonald
Keyword(s):  
Steady State ◽  
Ampa Receptor ◽  
Hippocampal Neurons ◽  
Time Course ◽  
Single Channel ◽  
Trivalent Cation ◽  
Receptor Desensitization ◽  
Whole Cell ◽  
Low Concentrations ◽  
Cultured Hippocampal Neurons

The actions of the trivalent cation Gd3+ on whole cell AMPA receptor-mediated currents were studied in isolated hippocampal neurons, in nucleated or outside-out patches taken from cultured hippocampal neurons, and on miniature excitatory postsynaptic currents (mEPSCs) recorded in cultured hippocampal neurons. Glutamate, AMPA, or kainate was employed to activate AMPA receptors. Applications of relatively low concentrations of Gd3+ (0.1–10 μM) substantially enhanced steady-state whole cell glutamate and kainate-evoked currents without altering peak currents, suggesting that desensitization was reduced. However, higher concentrations (>30 μM) depressed steady-state currents, indicating an underlying inhibition of channel activity. Lower concentrations of Gd3+also increased the potency of peak glutamate-evoked currents without altering that of steady-state currents. An ultrafast perfusion system and nucleated patches were then used to better resolve peak glutamate-evoked currents. Low concentrations of Gd3+ reduced peak currents, enhanced steady-state currents, and slowed the onset of desensitization, providing further evidence that this cation reduces desensitization. In the presence of cyclothiazide, a compound that blocks desensitization, a low concentration Gd3+ inhibited both peak and steady-state currents, indicating that Gd3+ both reduces desensitization and inhibits these currents. Gd3+ reduced the probability of channel opening at the peak of the currents but did not alter the single channel conductance calculated using nonstationary variance analysis. Recovery from desensitization was enhanced, and glutamate-evoked current activation and deactivation were slowed by Gd3+. The Gd3+-induced reduction in desensitization did not require the presence of the GluR2 subunit as this effect was seen in hippocampal neurons from GluR2 null-mutant mice. Gd3+ reduced the time course of decay of mEPSCs perhaps as a consequence of its slowing of AMPA receptor deactivation although an increase in the frequency of mEPSCs also suggested enhanced presynaptic release of transmitter. These results demonstrate that Gd3+ potently reduces AMPA receptor desensitization and mimics a number of the properties of the positive modulators of AMPA receptor desensitization such as cyclothiazide.

TXA2 agonists inhibit high-voltage-activated calcium channels in rat hippocampal CA1 neurons

1996 ◽  
Vol 271 (4) ◽  
pp. C1269-C1277 ◽  
Author(s):  
K. S. Hsu ◽  
C. C. Huang ◽  
W. M. Kan ◽  
P. W. Gean
Keyword(s):  
Hippocampal Neurons ◽  
Cell Voltage ◽  
Specific Protein ◽  
Dependent Manner ◽  
Concentration Dependent Manner ◽  
Whole Cell ◽  
Ca1 Neurons ◽  
Hippocampal Ca1 Neurons ◽  
Hippocampal Ca1 ◽  
Alpha 7

Whole cell voltage clamp recordings were used to investigate the effects of thromboxane A2 (TXA2) agonists on the voltage-dependent Ca2+ currents in rat hippocampal CA1 neurons. TXA2 agonists [1S-[1 alpha, 2 beta(5Z), 3 alpha(1E, 3S*)4 alpha ]]-7-[3-[3-hydroxy-4-(4'-iodophenoxy)-1-butenyl]-7-oxabicyclo [2,2,1]heptan-2-yl]-5-heptenoic acid (I-BOP) and U-46619, reversibly suppressed the whole cell Ca2+ currents in a concentration-dependent manner. The effect was blocked by specific TXA2 receptor antagonist, SQ-29548. I-BOP as well as U-46619 inhibited both omega-conotoxin GVIA (CgTx)-sensitive and nimodipine sensitive Ca2+ currents but had no effect on CgTx/nimodipine insensitive Ca2+ currents. The I-BOP and U-46619 inhibition of Ca2+ currents was blocked by internal dialysis of hippocampal neurons with specific protein kinase C (PKC) inhibitors, NPC-15437 and PKC inhibitor-(19-36). Pretreatment of hippocampal neurons with either 5 micrograms/ml pertussis toxin (PTX) or 5 micrograms/ml cholera toxin (CTX) did not significantly affect the suppression of the Ca2+ currents by I-BOP and U-46619. Dialyzing with 1 mM guanosine 5'-O-(3-thiotriphosphate) or 1 mM GDP significantly attenuated the I-BOP or U-46619 action. These results demonstrate that TXA2 agonists inhibit both CgTx- and nimodipine-sensitive Ca2+ currents but not CgTx/nimodipine-insensitive currents in rat hippocampal CA1 neurons via a PTX- and CTX-insensitive G protein-coupled activation of the PKC pathway.

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