scholarly journals An Allosteric Coagonist Model for Propofol Effects on α1β2γ2L γ-Aminobutyric Acid Type A Receptors

2012 ◽  
Vol 116 (1) ◽  
pp. 47-55 ◽  
Author(s):  
Dirk Ruesch ◽  
Elena Neumann ◽  
Hinnerk Wulf ◽  
Stuart A. Forman
Keyword(s):  
Type A ◽  
Receptor Activation ◽  
Convincing Evidence ◽  
Receptor Activity ◽  
Aminobutyric Acid ◽  
Single Class ◽  
Gaba A ◽  
Direct Activation ◽  
Receptor Sites ◽  
Acid Type

Background Propofol produces its major actions via γ-aminobutyric acid type A (GABA(A)) receptors. At low concentrations, propofol enhances agonist-stimulated GABA(A) receptor activity, and high propofol concentrations directly activate receptors. Etomidate produces similar effects, and there is convincing evidence that a single class of etomidate sites mediate both agonist modulation and direct GABA(A) receptor activation. It is unknown if the propofol binding site(s) on GABA(A) receptors that modulate agonist-induced activity also mediate direct activation. Methods GABA(A) α1β2γ2L receptors were heterologously expressed in Xenopus oocytes and activity was quantified using voltage clamp electrophysiology. We tested whether propofol and etomidate display the same linkage between agonist modulation and direct activation of GABA(A) receptors by identifying equiefficacious drug solutions for direct activation. We then determined whether these drug solutions produce equal modulation of GABA-induced receptor activity. We also measured propofol-dependent direct activation and modulation of low GABA responses. Allosteric coagonist models similar to that established for etomidate, but with variable numbers of propofol sites, were fitted to combined data. Results Solutions of 19 μM propofol and 10 μM etomidate were found to equally activate GABA(A) receptors. These two drug solutions also produced indistinguishable modulation of GABA-induced receptor activity. Combined electrophysiological data behaved in a manner consistent with allosteric coagonist models with more than one propofol site. The best fit was observed when the model assumed three equivalent propofol sites. Conclusions Our results support the hypothesis that propofol, like etomidate, acts at GABA(A) receptor sites mediating both GABA modulation and direct activation.

scholarly journals Two Etomidate Sites in α1β2γ2 γ-Aminobutyric Acid Type A Receptors Contribute Equally and Noncooperatively to Modulation of Channel Gating

2012 ◽  
Vol 116 (6) ◽  
pp. 1235-1244 ◽  
Author(s):  
Grigori Guitchounts ◽  
Deirdre S. Stewart ◽  
Stuart A. Forman
Keyword(s):  
Drug Effects ◽  
Type A ◽  
Aminobutyric Acid ◽  
Wild Type ◽  
Gaba A ◽  
Direct Activation ◽  
Type D ◽  
Acid Type ◽  
Hypnotic Agent ◽  
Mutant Receptors

Background Etomidate is a potent hypnotic agent that acts via γ-aminobutyric acid receptor type A (GABA(A)) receptors. Evidence supports the presence of two etomidate sites per GABA(A) receptor, and current models assume that each site contributes equally and noncooperatively to drug effects. These assumptions remain untested. Methods We used concatenated dimer (β2-α1) and trimer (γ2-β2-α1) GABA(A) subunit assemblies that form functional α1β2γ2 channels, and inserted α1M236W etomidate site mutations into both dimers (β2-α1M236W) and trimers (γ2-β2-α1M236W). Wild-type or mutant dimers (D(wt) or D(αM236W)) and trimers (T(wt) or T(αM236W)) were coexpressed in Xenopus oocytes to produce four types of channels: D(wt)T(wt), D(αM236W)T(wt), D(wt)T(αM236W), and D(αM236W)T(αM236W). For each channel type, two-electrode voltage clamp was performed to quantitatively assess GABA EC(50), etomidate modulation (left shift), etomidate direct activation, and other functional parameters affected by αM236W mutations. Results Concatenated wild-type D(wt)T(wt) channels displayed etomidate modulation and direct activation similar to α1β2γ2 receptors formed with free subunits. D(αM236W)T(αM236W) receptors also displayed altered GABA sensitivity and etomidate modulation similar to mutated channels formed with free subunits. Both single-site mutant receptors (D(αM236W)T(wt) and D(wt)T(αM236W)) displayed indistinguishable functional properties and equal gating energy changes for GABA activation (-4.9 ± 0.48 vs. -4.7 ± 0.48 kJ/mol, respectively) and etomidate modulation (-3.4 ± 0.49 vs. -3.7 ± 0.38 kJ/mol, respectively), which together accounted for the differences between D(wt)T(wt) and D(αM236W)T(αM236W) channels. Conclusions These results support the hypothesis that the two etomidate sites on α1β2γ2 GABA(A) receptors contribute equally and noncooperatively to drug interactions and gating effects.

Droperidol Inhibits GABAAand Neuronal Nicotinic Receptor Activation

2002 ◽  
Vol 96 (4) ◽  
pp. 987-993 ◽  
Author(s):  
Pamela Flood ◽  
Kristen M. Coates
Keyword(s):  
Type A ◽  
Receptor Activation ◽  
Aminobutyric Acid ◽  
Hill Coefficient ◽  
High Dose ◽  
Gamma Aminobutyric Acid ◽  
Anesthetic Drugs ◽  
Gaba Inhibition ◽  
Acid Type ◽  
Anesthetic Action

Background Droperidol is used in neuroleptanesthesia and as an antiemetic. Although its antiemetic effect is thought to be caused by dopaminergic inhibition, the mechanism of droperidol's anesthetic action is unknown. Because gamma-aminobutyric acid type A (GABAA) and neuronal nicotinic acetylcholine receptors (nAChRs) have been implicated as putative targets of other general anesthetic drugs, the authors tested the ability of droperidol to modulate these receptors. Methods gamma-Aminobutyric acid type A alpha1beta1gamma2 receptor, alpha7 and alpha4beta2 nAChRs were expressed in Xenopus oocytes and studied with two-electrode voltage clamp recording. The authors tested the ability of droperidol at concentrations from 1 nm to 100 microm to modulate activation of these receptors by their native agonists. Results Droperidol inhibited the GABA response by a maximum of 24.7 +/- 3.0%. The IC50 for inhibition was 12.6 +/- 0.47 nm droperidol. At high concentrations, droperidol (100 microm) activates the GABAA receptor in the absence of GABA. Inhibition of the GABA response is significantly greater at hyperpolarized membrane potentials. The activation of the alpha7 nAChR is also inhibited by droperidol, with an IC50 of 5.8 +/- 0.53 microm. The Hill coefficient is 0.95 +/- 0.1. Inhibition is noncompetitive, and membrane voltage dependence is insignificant. Conclusions Droperidol inhibits activation of both the GABAA alpha1beta1gamma2 and alpha7 nAChR. The submaximal GABA inhibition occurs within a concentration range such that it might be responsible for the anxiety, dysphoria, and restlessness that limit the clinical utility of high-dose droperidol anesthesia. Inhibition of the alpha7 nAChR might be responsible for the anesthetic action of droperidol.

scholarly journals Propofol at Clinically Relevant Concentrations Increases Neuronal Differentiation But Is Not Toxic to Hippocampal Neural Precursor Cells In Vitro 

2012 ◽  
Vol 117 (5) ◽  
pp. 1080-1090 ◽  
Author(s):  
Jeffrey W. Sall ◽  
Greg Stratmann ◽  
Jason Leong ◽  
Elliott Woodward ◽  
Philip E. Bickler
Keyword(s):  
Cell Death ◽  
Lactate Dehydrogenase ◽  
Neuronal Differentiation ◽  
Cell Function ◽  
Type A ◽  
Receptor Activation ◽  
Aminobutyric Acid ◽  
Neural Precursor ◽  
Acid Type

Background Propofol in the early postnatal period has been shown to cause brain cell death. One proposed mechanism for cognitive dysfunction after anesthesia is alteration of neural stem cell function and neurogenesis. We examined the effect of propofol on neural precursor or stem cells (NPCs) grown in vitro. Methods Hippocampal-derived NPCs from postnatal day 2 rats were exposed to propofol or Diprivan. NPCs were then analyzed for bromodeoxyuridine incorporation to measure proliferation. Cell death was measured by lactate dehydrogenase release. Immunocytochemistry was used to evaluate the expression of neuronal and glial markers in differentiating NPCs exposed to propofol. Results Propofol dose dependently increases the release of lactate dehydrogenase from NPCs under both proliferating and differentiating conditions at supraclinical concentrations (more than 7.1 µM). Both Diprivan and propofol had the same effect on NPCs. Propofol-mediated release of lactate dehydrogenase is not inhibited by blocking the γ-aminobutyric acid type A receptor or extracellular calcium influx and is not mediated by caspase-3/7. Direct γ-aminobutyric acid type A receptor activation did not have the same effect. In differentiating NPCs, 6 h of propofol at 2.1 µM increased the number neurons but not glial cells 4 days later. Increased neuronal differentiation was not blocked by bicuculline. Conclusions Only supraclinical concentrations of propofol or Diprivan kill NPCs in culture by a non-γ-aminobutyric acid type A, noncaspase-3 mechanism. Clinically relevant doses of propofol increase neuronal fate choice by a non-γ-aminobutyric acid type A mechanism.

scholarly journals A Conserved Tyrosine in the β2Subunit M4 Segment Is a Determinant of γ-Aminobutyric Acid Type A Receptor Sensitivity to Propofol

2007 ◽  
Vol 107 (3) ◽  
pp. 412-418 ◽  
Author(s):  
James E. Richardson ◽  
Paul S. Garcia ◽  
Kate K. O'Toole ◽  
Jason M. C. Derry ◽  
Shannon V. Bell ◽  
...  
Keyword(s):  
Binding Site ◽  
Type A ◽  
Receptor Activation ◽  
Aminobutyric Acid ◽  
Gamma Aminobutyric Acid ◽  
General Anesthetics ◽  
Receptor Function ◽  
293 Cells ◽  
Acid Type ◽  
Normal Sensitivity

Background The gamma-aminobutyric acid type A receptor (GABAA-R) beta subunits are critical targets for the actions for several intravenous general anesthetics, but the precise nature of the anesthetic binding sites are unknown. In addition, little is known about the role the fourth transmembrane (M4) segment of the receptor plays in receptor function. The aim of this study was to better define the propofol binding site on the GABAA-R by conducting a tryptophan scan in the M4 segment of the beta2 subunit. Methods Seven tryptophan mutations were introduced into the C-terminal end of the M4 segment of the GABAA-R beta2 subunit. GABAA-R subunit complementary DNAs were transfected into human embryonic kidney 293 cells grown on glass coverslips. After transfection (36-72 h), coverslips were transferred to a perfusion chamber to assay receptor function. Cells were whole cell patch clamped and exposed to GABA, propofol, etomidate, and pregnenolone. Chemicals were delivered to the cells using two 10-channel infusion pumps and a rapid solution exchanger. Results All tryptophan mutations were well tolerated, and with one exception, all resulted in minimal changes in receptor activation by GABA. One mutation, beta2(Y444W), selectively suppressed the ability of propofol to enhance receptor function while retaining normal sensitivity to etomidate and pregnenolone. Conclusions This is the first report of a mutation that selectively reduces propofol sensitivity without altering the action of etomidate. The reduction in propofol sensitivity is consistent with the loss of a hydrogen bond within the propofol binding site. These results also suggest a possible orientation of the propofol molecule within its binding site.

Modulation of γ-Aminobutyric Acid Type A Receptor–mediated Spontaneous Inhibitory Postsynaptic Currents in Auditory Cortex by Midazolam and Isoflurane

2005 ◽  
Vol 102 (5) ◽  
pp. 962-969 ◽  
Author(s):  
Yakov I. Verbny ◽  
Elliott B. Merriam ◽  
Matthew I. Banks
Keyword(s):  
Auditory Cortex ◽  
Pyramidal Cells ◽  
Type A ◽  
Aminobutyric Acid ◽  
Gaba A ◽  
Cellular Targets ◽  
Inhibitory Postsynaptic Currents ◽  
Postsynaptic Currents ◽  
Acid Type

Background Anesthetic agents that target gamma-aminobutyric acid type A (GABA(A)) receptors modulate cortical auditory evoked responses in vivo, but the cellular targets involved are unidentified. Also, for agents with multiple protein targets, the relative contribution of modulation of GABA(A) receptors to effects on cortical physiology is unclear. The authors compared effects of the GABA(A) receptor-specific drug midazolam with the volatile anesthetic isoflurane on spontaneous inhibitory postsynaptic currents (sIPSCs) in pyramidal cells of auditory cortex. Methods Whole cell recordings were obtained in murine brain slices at 34 degrees C. GABA(A) sIPSCs were isolated by blocking ionotropic glutamate receptors. Effects of midazolam and isoflurane on time course, amplitude, and frequency of sIPSCs were measured. Results The authors detected no effect of midazolam at 0.01 microM on sIPSCs, whereas midazolam at 0.1 and 1 microM prolonged the decay of sIPSCs by approximately 25 and 70%, respectively. Isoflurane at 0.1, 0.25, and 0.5 mm prolonged sIPSCs by approximately 45, 150, and 240%, respectively. No drug-specific effects were observed on rise time or frequency of sIPSCs. Isoflurane at 0.5 mm caused a significant decrease in sIPSC amplitude. Conclusions The dose dependence of isoflurane effects on GABA(A) sIPSCs in pyramidal cells is consistent with effects on auditory evoked response in vivo. By contrast, comparable effects of midazolam on GABA(A) sIPSCs arise at concentrations exceeding those currently thought to be achieved in vivo, suggesting that the cellular targets of midazolam reside elsewhere in the thalamocortical circuit or that the concentration of midazolam reached in the brain is higher than currently believed.

Effects of Isoflurane on γ-Aminobutyric Acid Type A Receptors Activated by Full and Partial Agonists

2003 ◽  
Vol 98 (2) ◽  
pp. 306-311 ◽  
Author(s):  
Norbert Topf ◽  
Andrew Jenkins ◽  
Nicole Baron ◽  
Neil L. Harrison
Keyword(s):  
Gaba Receptor ◽  
Partial Agonist ◽  
Type A ◽  
Aminobutyric Acid ◽  
Hek293 Cells ◽  
Relative Efficacy ◽  
Gaba A ◽  
Mutant Receptor ◽  
Acid Type ◽  
Beta 2

Background Volatile anesthetics prolong inhibitory postsynaptic potentials in central neurons an allosteric action on the gamma-aminobutyric acid type A (GABA(A)) receptor, an effect that may underlie the hypnotic actions of these agents. Inhaled anesthetics such as isoflurane act to enhance responses to submaximal concentrations of GABA, but it is not clear whether their effect is mediated by an increase in the binding of the agonist or by changes in receptor gating behavior. To address this question, the authors studied the effects of isoflurane on a mutant GABA(A) receptor with a gating defect that decreases receptor sensitivity by lowering agonist efficacy. They then compared the effects of clinically relevant concentrations of isoflurane on the actions of GABA and piperidine-4-sulfonic acid (P4S), a partial agonist at the GABA(A) receptor. Methods The authors created a mutant of the GABA receptor alpha subunit (L277A) by site-directed mutagenesis. The mutant subunit was coexpressed with beta(2) and gamma(2S) subunits in HEK293 cells, and responses to GABA and P4S were recorded using the whole-cell patch clamp technique. EC values were determined for the full agonist GABA and the partial agonist P4S. The authors also determined the relative efficacy (epsilon) of P4S. These measurements were then repeated in the presence of isoflurane. Results The concentration-response curve for GABA was shifted to the right (EC(50) = 278 microm) in the alpha(1)(L277A)beta(2)gamma(2S) mutant receptor, compared with the corresponding wild-type alpha(1)beta(2)gamma(2S) GABA(A) receptor (EC(50) = 16 microm). P4S is a partial agonist at both receptors, with a dramatically decreased relative efficacy at the mutant receptor (epsilon = 0.24). When the mutant receptor was studied in the presence of isoflurane, the concentration-response curves for both GABA and P4S were shifted to the left (EC(50) for GABA = 78 microm); the efficacy of P4S also increased significantly (epsilon = 0.40). Conclusion By studying a mutant GABA receptor with impaired gating, the authors were able to demonstrate clearly that isoflurane can increase the efficacy of a partial agonist, as well as increase agonist potency. These data suggest that the volatile anesthetic isoflurane exerts at least some of its effects on the GABA(A) receptor via alterations in gating rather than simply changing binding or unbinding of the agonist.

scholarly journals Synthesis of novel cognition enhancers with pyrazolo[5,1- c ][1,2,4]benzotriazine core acting at γ-aminobutyric acid type A (GABA A ) receptor

2013 ◽  
Vol 21 (8) ◽  
pp. 2186-2198 ◽  
Author(s):  
Gabriella Guerrini ◽  
Giovanna Ciciani ◽  
Annarella Costanzo ◽  
Simona Daniele ◽  
Claudia Martini ◽  
...  
Keyword(s):  
Type A ◽  
Aminobutyric Acid ◽  
Gaba A ◽  
Acid Type

scholarly journals γ-Aminobutyric Acid Type A (GABAA) Receptor Activation Modulates Tau Phosphorylation

2012 ◽  
Vol 287 (9) ◽  
pp. 6743-6752 ◽  
Author(s):  
Niko-Petteri Nykänen ◽  
Kai Kysenius ◽  
Prasanna Sakha ◽  
Päivi Tammela ◽  
Henri J. Huttunen
Keyword(s):  
Gabaa Receptor ◽  
Type A ◽  
Receptor Activation ◽  
Tau Phosphorylation ◽  
Aminobutyric Acid ◽  
Acid Type

Gamma-Aminobutyric Acid Type A Receptor Genes and Their Related Epilepsies

2021 ◽  
Author(s):  
Viviana Brafa Musicoro ◽  
Vincenzo Sortino ◽  
Giulia Pecora ◽  
Monica Tosto ◽  
Manuela Lo Bianco ◽  
...  
Keyword(s):  
Gaba Receptors ◽  
Type A ◽  
Autism Spectrum ◽  
Aminobutyric Acid ◽  
Gamma Aminobutyric Acid ◽  
Phenotype Correlation ◽  
Gaba A ◽  
Genotype Phenotype Correlation ◽  
Acid Type ◽  
Neuropsychiatric Diseases

AbstractGamma-aminobutyric acid type A (GABA-A) receptor subunit gene mutations, which include GABRA1, GABRB3, GABRD, and GABRG2, are often involved in several genetic epilepsy syndromes and other neuropsychiatric diseases like autism spectrum disorder, schizophrenia, and anxiety. GABA-A are ligand-gated ionic channels, and are involved firstly in the fast inhibitory synaptic transmission of the central nervous system. The GABA receptors include the ionotropic GABA-A and GABA-C receptors and the metabotropic GABA-B receptors. According to the site in which mutations occur, they cause disorders in channel opening, “lock-and-pull” receptor system functioning, and capable of causing a specific epilepsy phenotype. The aim of this article is to summarize the most recent literature findings, considering genetic mutations, clinical features, genotype/phenotype correlation, and therapy about neurodevelopment diseases correlated to GABA receptors dysfunction, in particular epilepsy. According to our findings, we conclude that further mutation analysis could permit genotype–phenotype correlation and give more information about the best efficient treatment, even if—at present—more clinical and genetic studies are necessary.

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