Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “allosteric modulation”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 415 records · Page 23Linked to original sources
PubMed1997

Rapid seizure-induced reduction of benzodiazepine and Zn2+ sensitivity of hippocampal dentate granule cell GABAA receptors.

Fast synaptic inhibition in the forebrain is mediated primarily by GABA acting on GABAA receptors (GABARs). GABARs are regulated by numerous positive (barbiturates, benzodiazepines, and neurosteroids) and negative (picrotoxin, bicuculline, and Zn2+) allosteric modulators. The sensitivity of GABARs to GABA and to allosteric modulators changes gradually during normal development, during development of chronic epilepsy, and after prolonged exposure to GABAR agonists. Here we report the development of rapid functional plasticity of GABARs occurring over 45 min of continuous seizures (status epilepticus) in rats. Seizures induced in rats by administration of lithium followed by pilocarpine were readily terminated by the benzodiazepine diazepam when administered early during the seizures (after 10 min of seizures). However, during status epilepticus, there was a substantial reduction of diazepam potency for termination of the seizures. To determine whether the loss of sensitivity of the animals to diazepam was caused by an alteration of GABAR functional properties, we obtained whole-cell GABAR currents from hippocampal dentate granule cells isolated acutely from control rats and from rats undergoing status epilepticus. GABAR properties were characterized by determining GABA sensitivity and the sensitivity of GABARs to regulation by benzodiazepines, barbiturates, and Zn2+. When compared with those from naive controls, GABAR currents from rats undergoing status epilepticus were less sensitive to diazepam and Zn2+ but retained their sensitivity to GABA and pentobarbital. We conclude that the prolonged seizures of status epilepticus rapidly altered the functional properties of hippocampal dentate granule cell GABARs.

Animals↗
PubMed2004

Imidazenil: a potent and safe protective agent against diisopropyl fluorophosphate toxicity.

Convulsions are major and life-threatening signs of organophosphate (OP) nerve agents induced neurotoxicity. Thus, early intervention with anticonvulsant drugs to control seizure propagation and the consequent irreversible neuronal damage that may occur during OP exposure is essential. Diazepam is the standard anticonvulsant used in the therapeutic management of OP poisoning. However, its use has been associated with several unwanted effects including, sedation, amnesia, and in the large doses used for such treatment, respiratory depression. Moreover, protracted administration of diazepam has been associated with tolerance and dependence liabilities. In this study, we compared the efficacy and safety of diazepam (full allosteric modulator of GABA action) to that of imidazenil (partial, selective allosteric modulator of GABA action) as preventive treatment against diisopropyl fluorophosphate (DFP)-induced convulsions and mortality. Our results show that imidazenil is more potent and efficacious than diazepam in protecting rats against DFP-induced convulsions and death. Moreover, imidazenil was effective at doses (1 and 0.5 mg/kg) we have previously shown to be devoid of sedation, amnesia, respiratory depression, or tolerance and/or dependence. In contrast, diazepam was effective at doses (5 and 2.5 mg/kg) that produce sedation, amnesia, and ataxia. Furthermore, the combination of imidazenil with atropine was more potent and efficacious than that with diazepam.

Animals↗
PubMed2005

An intersubunit zinc binding site in rat P2X2 receptors.

P2X receptors are ATP-gated ion channels made up of three similar or identical subunits. It is unknown whether ligand binding is intersubunit or intrasubunit, either for agonists or for allosteric modulators. Zinc binds to rat P2X2 receptors and acts as an allosteric modulator, potentiating channel opening. To probe the location of this zinc binding site, P2X2 receptors bearing mutations of the histidines at positions 120 and 213 were expressed in Xenopus oocytes. Studies of H120C and H213C mutants produced five lines of evidence consistent with the hypothesis that the residues in these positions bind zinc. Mixing of subunits containing the H120A or H213A mutation generated receptors that showed zinc potentiation, even though neither of these mutant receptors showed zinc potentiation on its own. Furthermore, expression of trimeric concatamers with His --> Ala mutations at some but not all six positions showed that zinc potentiation correlated with the number of intersubunit histidine pairs. These results indicate that zinc potentiation requires an interaction across a subunit interface. Expression of the H120C/H213C double mutant resulted in the formation of ectopic disulfide bonds that could be detected by changes in the physiological properties of the receptors after treatment with reducing and oxidizing agents. Immunoblot analysis of H120C/H213C protein separated under nonreducing conditions demonstrated that the ectopic bonds were between adjacent subunits. Taken together, these data indicate that His120 and His213 sit close to each other across the interface between subunits and are likely to be key components of the zinc binding site in P2X2 receptors.

Adenosine Triphosphate↗
PubMed2002

G protein-coupled receptor allosterism and complexing.

G protein-coupled receptors (GPCRs) represent the largest family of cell-surface receptors. These receptors are natural allosteric proteins because agonist-mediated signaling by GPCRs requires a conformational change in the receptor protein transmitted between two topographically distinct binding sites, one for the agonist and another for the G protein. It is now becoming increasingly recognized, however, that the agonist-bound GPCR can also form ternary complexes with other ligands or "accessory" proteins and display altered binding and/or signaling properties in relation to the binary agonist-receptor complex. Allosteric sites on GPCRs represent novel drug targets because allosteric modulators possess a number of theoretical advantages over classic orthosteric ligands, such as a ceiling level to the allosteric effect and a potential for greater GPCR subtype-selectivity. Because of the noncompetitive nature of allosteric phenomena, the detection and quantification of such effects often relies on a combination of equilibrium binding, nonequilibrium kinetic, and functional signaling assays. This review discusses the development and properties of allosteric receptor models for GPCRs and the detection and quantification of allosteric effects. Moreover, we provide an overview of the current knowledge regarding the location of possible allosteric sites on GPCRs and candidate endogenous allosteric modulators. Finally, we discuss the potential for allosteric effects arising from the formation of GPCR oligomers or GPCRs complexed with accessory cellular proteins. It is proposed that the study of allosteric phenomena will become of progressively greater import to the drug discovery process due to the advent of newer and more sensitive GPCR screening technologies.

Allosteric Regulation↗
PubMed2005

Role of the alpha subunit in the modulation of GABA(A) receptors by anabolic androgenic steroids.

Neural transmission mediated by circuits expressing alpha2 subunit-containing gamma-aminobutyric acid type A (GABA(A)) receptors is critical for the expression of behaviors known to be altered by anabolic androgenic steroids (AAS). Here we show that micromolar concentrations of AAS, which reflect levels found in steroid abusers, induce positive modulation of currents from alpha2beta3 gamma2L recombinant receptors elicited by pulses of GABA that mimic synaptic conditions in a manner that is mechanistically distinct from modulation induced at alpha1beta3 gamma2L receptors. Specifically, at alpha2-containing receptors, the AAS, 17alpha-methyltestosterone (17alpha-MeT) enhanced peak current, slowed deactivation, diminished desensitization, and promoted entry of receptors into more distal states along the activation pathway. Analysis of GABA(A) receptor-mediated synaptic currents in primary cortical neurons followed by single cell real-time RT-PCR demonstrated that 17alpha-MeT enhancement of synaptic currents is proportional to the ratio of alpha2 to alpha1 subunit mRNA. Finally, we show that the modulation elicited by AAS is not comparable to that produced by micromolar concentrations of other positive allosteric modulators at alpha2-containing receptors. In sum, these data indicate that AAS elicit effects on GABA(A) receptor function that depend significantly on alpha subunit composition and that the mechanism of AAS modulation of GABA(A) receptors is distinct from that of other positive allosteric modulators.

Anabolic Agents↗
PubMed1994

Allosteric effects of the alkane-bis-ammonium compound W84 and of tacrine on [3H]pirenzepine binding at M1-receptors in rat cerebral cortex.

The bis-quaternary W84, hexamethylene-bis-[dimethyl-(3-phthalimidopropyl)-ammonium bromide], is a potent allosteric modulator of M2-cholinoceptors. In this study we aimed at quantifying its allosteric effect on the dissociation of [3H]pirenzepine from M1-cholinoceptors in rat cerebral cortex and to measure the effects on association and equilibrium binding of [3H]pirenzepine. For sake of comparison tacrine was included which is known to be a potent allosteric modulator of [3H]pirenzepine binding to M1-receptors. Under control conditions (3 mM MgHPO4, 50 mM Tris-HCl, pH 7.4, 23 degrees) [3H]pirenzepine binding was characterized by KD = 5 nM and Bmax = 965 fmol/mg membrane protein, the rate constants amounting to k+1 = 5.0 microM-1 x min-1 and k-1 = 0.031 min-1. W84 and tacrine reduced [3H]pirenzepine binding concentration-dependently with IC50-values of 1.9 microM and 2.6 microM, respectively. [3H]pirenzepine association was inhibited by the compounds with EC50,ass = 1.8 microM for W84 and EC50,ass = 2.4 microM for tacrine. The concentrations reducing the dissociation rate by 50% amounted to EC50,diss = 21 microM for W84 and to EC50,diss = 54 microM for tacrine. Compared with W84, the dose-reponse curves of tacrine for the investigated effects were significantly steeper. In conclusion, WS84 affected [3H]pirenzepine binding to M1-receptors allosterically with a higher potency than tacrine but probably by a different mechanism.

Allosteric Regulation↗
PubMed2006

Mutational disruption of a conserved disulfide bond in muscarinic acetylcholine receptors attenuates positive homotropic cooperativity between multiple allosteric sites and has subtype-dependent effects on the affinities of muscarinic allosteric ligands.

The 2nd outer loop (o2) of muscarinic acetylcholine receptors (mAChRs) contains a highly conserved cysteine residue that is believed to participate in a disulfide bond and is flanked on either side by epitopes that are critical to the binding of many muscarinic allosteric modulators. We determined the allosteric binding parameters of the modulators gallamine, W84, and tetrahydroaminoacridine (THA) at M2 and M3 mAChRs in which these cysteine residues had been mutated to alanines. THA is known to bind to mAChRs with a strong positive homotropic cooperativity (a Hill slope of approximately 2) that implies that it must interact with multiple allosteric sites. The disulfide cysteine mutations in M2 receptors reduced the allosteric potencies of the tested modulators as if the critical adjacent residue (Tyr177) itself had been mutated. However, in M3 receptors, the disulfide cysteine mutations had no effect on the potencies of gallamine or W84 and even increased the potency of THA. It was most interesting that the strong, positive, homotropic interactions of THA at both M2 and M3 receptors were markedly reduced by the cysteine mutations. In addition, gallamine also displayed positive homotropic cooperativity in its interactions with M3 receptors (but not M2 receptors), and this cooperativity was not evident in the cysteine mutants. Thus, it seems that these cysteine residues play a role in linking cooperating allosteric sites, although it is not currently possible to say whether these multiple sites lie within one receptor or on two linked receptors of a dimer or higher order oligomer.

Allosteric Site↗
PubMed1998

Functional changes in rat nigral GABA(A) receptors induced by degeneration of the striatonigral GABAergic pathway: an electrophysiological study of receptors incorporated into Xenopus oocytes.

Expression of rat brain gamma-aminobutyric acid type A (GABA(A)) receptors in Xenopus laevis oocytes can be achieved by injection of the oocytes with synaptosomes. This approach has now been applied to evaluate changes in the function of nigral GABA(A) receptors after degeneration of the striatonigral GABAergic pathway induced by the unilateral infusion of kainic acid into the rat striatum. Ten days after striatal injection, synaptosomal membranes were prepared from the substantia nigra and introduced into oocytes. Nigral GABA(A) receptors incorporated into the oocyte cell membrane were then characterized electrophysiologically under voltage-clamp conditions. The maximal amplitude of GABA-induced Cl- currents in oocytes injected with synaptosomes from denervated substantia nigra was twice that observed in oocytes injected with synaptosomes from control substantia nigra. The concentration of GABA required for the half-maximal response did not differ between the two groups of oocytes. In addition, the potentiation of GABA-induced currents by the benzodiazepine diazepam (1 microM) and the steroid derivative allopregnanolone (3 microM) was increased by approximately 65 and 60%, respectively, in oocytes injected with synaptosomes from denervated substantia nigra compared with those injected with control synaptosomes. The concentrations of diazepam and allopregnanolone giving half-maximal responses were not affected by denervation. In contrast, the inhibitory effects of the benzodiazepine receptor inverse agonists FG 7142 (10 microM) and 6,7-dimethoxy-4-ethyl-beta-carboline-3-carboxylic acid ethyl ester (1 microM) were reduced by 48 and 38%, respectively, after denervation. These results indicate that the up-regulation of nigral GABA(A) receptors induced by degeneration of the striatonigral GABAergic pathway is associated with an increased efficacy of positive allosteric modulators, such as benzodiazepines and steroids, and with a reduced efficacy of negative allosteric modulators such as beta-carbolines.

Animals↗
PubMed2005

Benzodiazepine modulation of partial agonist efficacy and spontaneously active GABA(A) receptors supports an allosteric model of modulation.

Benzodiazepines (BZDs) have been used extensively for more than 40 years because of their high therapeutic index and low toxicity. Although BZDs are understood to act primarily as allosteric modulators of GABA(A) receptors, the mechanism of modulation is not well understood. The applicability of an allosteric model with two binding sites for gamma-aminobutyric acid (GABA) and one for a BZD-like modulator was investigated. This model predicts that BZDs should enhance the efficacy of partial agonists. Consistent with this prediction, diazepam increased the efficacy of the GABA(A) receptor partial agonist kojic amine in chick spinal cord neurons. To further test the validity of the model, the effects of diazepam, flurazepam, and zolpidem were examined using wild-type and spontaneously active mutant alpha1(L263S)beta3gamma2 GABA(A) receptors expressed in HEK-293 cells. In agreement with the predictions of the allosteric model, all three modulators acted as direct agonists for the spontaneously active receptors. The results indicate that BZD-like modulators enhance the amplitude of the GABA response by stabilizing the open channel active state relative to the inactive state by less than 1 kcal, which is similar to the energy of stabilization conferred by a single hydrogen bond.

Allosteric Regulation↗
PubMed1986

Glutamate-containing dipeptides do not modulate ligand binding at excitatory amino acid receptors.

Dipeptides of the structure X-Glu (e.g. X = Phe, Leu) have been proposed as allosteric modulators of excitatory amino acid receptors in rat brain membranes. Here we report that these dipeptides reduce the binding of L-[3H]Glu (predominantly N-methyl-D-aspartate-sensitive sites) and of [3H]kainate to postsynaptic density preparations isolated from rat brain. However, several observations indicate that the effects of these dipeptides are mediated not by allosteric modulation, but by free L-Glu liberated by the actions of a membrane-associated aminopeptidase. The absolute and relative potencies of the dipeptides are similar at all acidic amino acid binding sites examined to date, suggesting the involvement of a factor with similar activity at each site (e.g. L-Glu). N-Acetyl-Met-Glu is a weak inhibitor of L-Glu and kainate binding, and N-blocked peptides are known to be poor substrates of aminopeptidases. Bestatin, an inhibitor of aminopeptidases, decreases or abolishes the effects of substrate dipeptides on L-Glu and kainate receptor binding, while having no effect itself.

2-Amino-5-phosphonovalerate↗
PubMed1992

[35S]sadopine, a novel high affinity, high specific activity, L-type Ca2+ channel probe: characterization of two equipotent diastereomers with opposite allosteric properties.

A novel 35S-labeled dihydropyridine (DHP), 1,4-dihydro-2,6-dimethyl-4-(2-trifluoromethylphenyl)-pyridine-3,5-dic arboxyl-3- [2-(N-tert-butoxycarbonyl-L-[35S]methionyl)-aminoethyl]-ester-5-ethyl ester, ([35S]sadopine) (800-1400 Ci/mmol), the respective (+)- and (-)-diastereomers, and unlabeled (+/- )-, (-)-, and (+)-sadopine were synthesized. [35S]Sadopine is an excellent high affinity, high specific activity radioligand to label selectively the DHP receptor of L-type Ca2+ channels in tissue sections as well as in membrane fragments. Both diastereomers bind to the DHP receptors in a saturable and reversible manner, with equal, subnanomolar, dissociation constants. Despite their similar affinities, (+)- and (-)-sadopine differ with respect to their kinetic properties [the association and dissociation rate constants are 10-fold higher for (+)-[35S]sadopine at 22 degrees] and their allosteric modulation of the phenylaklylamine or benzothiazepine binding domain. (+)-Sadopine is a negative but (-)-sadopine a positive allosteric modulator of (-)-[N-methyl-3H]LU49888 or (+)-cis-[3H] diltiazem binding at 30 degrees. Both diastereomers act as L-type Ca2+ channel blockers in cardiac and smooth muscle cells. Computer-based analysis of the electrostatic potentials of the two diastereomers and calculation of the interaction energies with a hypothetical DHP receptor model predicted not only the similar affinities of (+)- and (-)-sadopine but also their Ca2+ channel-blocking effects. The temperature-dependent allosteric differences between the diastereomers suggest that two distinct conformational states of the DHP receptor are stabilized in vitro, both corresponding to a nonconducting state of the channel. Our data indicate that access to the DHP receptor site, but not binding affinity, is a function of the opposite stereochemistry of the sadopine diastereomers. Therefore, labeled and unlabeled (+)- and (-)-sadopine will be useful probes to further characterize the molecular basis of DHP-Ca2+ channel interaction and the pharmacological and physiological significance of the different allosteric conformations of the channel induced by Ca2+ channel-active drugs.

Animals↗
PubMed1997

[Intravenous anesthetics, acting on the gamma-amino butric acid (GABA)A receptor, potentiate the herbal medicine "saiko-keishi-to"-induced chloride current].

We have reported that the Japanese herbal medicine "Saiko-Keishi-To" (SK) which is often used for treating epileptic patients activates the GABAA receptor-mediated chloride current (Icl). In the present study, we examined whether the SK-induced Icl could be potentiated by several intravenous anesthetics known to interact with the GABAA receptor, and also examined whether SK could potentiate the GABA-induced Icl. Whole-cell patch-clamp recordings were made from cultured rat dorsal root ganglion cells. The peak amplitude of the Icl evoked by SK (2 mg.ml-1) increased after pentobarbital (50 microM) to 184 +/- 26% (n = 5), diazepam (1 microM) to 166 +/- 29% (n = 5), and propofol (5 microM) to 294 +/- 93% (n = 5) from their respective controls, while the anesthetics did not activate the Icl by themselves. The peak amplitude of the Icl evoked by GABA (10 microM) increased after propofol (5 microM) to 617 +/- 189% of the control (n = 4), but decreased to 84 +/- 7% of the control by SK (0.2 mg.ml-1, n = 4). These results indicate that the SK-induced Icl can be potentiated by the intravenous anesthetics, positive allosteric modulators of the GABAA receptor-Cl- channel complex and that SK is not a positive allosteric modulator, but a partial agonist for the GABAA receptor. Our study thus suggests that the combined use of SK and anticonvulsants such as barbiturates and benzodiazepines may be more effective in treating epileptic patients than SK alone.

Anesthetics, Intravenous↗
PubMed2006

Fluoxetine and norfluoxetine stereospecifically and selectively increase brain neurosteroid content at doses that are inactive on 5-HT reuptake.

It has recently become more clearly understood that in human brain pathophysiology, neurosteroids play a role in anxiety disorders, premenstrual syndrome, postpartum depression, posttraumatic stress disorder, and depression. In the treatment of major depression, recent clinical studies indicate that the pharmacological profiles of fluoxetine and fluvoxamine are correlated with the ability of these drugs to increase the brain and cerebrospinal fluid content of allopregnanolone (Allo), a potent positive allosteric modulator of gamma-aminobutyric acid (GABA) action at GABAA receptors. Thus, the neurosteroid-induced positive allosteric modulation of GABA action at GABAA receptors is facilitated by fluoxetine or its congeners (i.e., paroxetine, fluvoxamine, sertraline), which may not block 5-HT reuptake at the doses currently prescribed in the clinic. However, these doses are effective in the treatment of premenstrual dysphoria, anxiety, and depression. In socially isolated mice, we tested the hypothesis that fluoxetine, norfluoxetine, and other specific serotonin reuptake inhibitor (SSRI) congeners stereoselectively upregulate neurosteroid content at doses insufficient to inhibit 5-HT reuptake; although they potentiate pentobarbital-induced sedation and exert antiaggressive action. Very importantly, the inhibition of 5-HT reuptake lacks stereospecificity and requires fluoxetine and norfluoxetine doses that are 50-fold greater than those required to increase brain Allo content, potentiate the action of pentobarbital, or antagonize isolation-induced aggression. Based on these findings, it could be inferred that the increase of brain Allo content elicited by fluoxetine and norfluoxetine, rather than the inhibition selective of 5-HT reuptake, may be operative in the fluoxetine-induced remission of the behavioral abnormalities associated with mood disorders. Therefore, the term "SSRI" may be misleading in defining the pharmacological profile of fluoxetine and its congeners. To this extent, the term "selective brain steroidogenic stimulants" (SBSSs) could be proposed.

Animals↗
PubMed2004

A GABAergic cortical deficit dominates schizophrenia pathophysiology.

Several lines of evidence support the role of an epigenetic-induced GABAergic cortical dysfunction in schizophrenia psychopathology, which is probably dependent on an increase in the expression of DNA-methyltransferase-1 occurring selectively in GABAergic neurons. The key enzyme regulating GABA synthesis, termed glutamic acid decarboxylase 67 (GAD67) and the important neurodevelopmental protein called reelin are coexpressed in GABAergic neurons. Upon release, GABA and reelin bind to postsynaptic receptors located in dendrites, somata, or the axon initial segment of pyramidal neurons. Because GAD67 and reelin are downregulated in schizophrenia, it is suggested that schizophrenics may express GABAergic deficit-related alterations of pyramidal neuron function. A reduction of dendritic spines is a finding reported in the prefrontal cortex of schizophrenia patients. Because dendritic spines are innervated by glutamatergic axon terminals, very probably this reduction of dendritic spine expression is translated into a functional deficit of glutamatergic transmission. Plastic modifications of neuronal circuits are probably dependent on GABAergic transmitter tone, and it is likely that GABAergic dysfunction is at the root of synaptic plasticity deficits in schizophrenia. Thus, a possible avenue for the treatment of schizophrenia would be to address this GABAergic functional deficit using positive allosteric modulators of the action of GABA at GABAA receptors. Benzodiazepines (BZ) such as diazepam are effective in treating positive and negative symptoms of schizophrenia, but because they positively modulate GABAA receptors expressing alpha1 subunits, these BZs cause sedation and tolerance. In contrast, imidazenil, a full allosteric modulator of GABAA receptors expressing alpha5 subunits may reduce psychotic symptomatology without producing sedation. Hence, imidazenil should be appropriately studied as a prospective candidate for a pharmacological intervention in schizophrenia.

Animals↗
PubMed2000

Plasma 5alpha-androstane-3alpha,17betadiol, an endogenous steroid that positively modulates GABA(A) receptor function, and anxiety: a study in menopausal women.

We tested the hypothesis that changes in endogenous neuroactive steroids acting as positive allosteric modulators of gamma-aminobutyric acid (GABA)(A) receptors may be related to the menopause-associated mood alterations. The study sample consisted of twenty five drug-free menopausal women, 1-3 years since the onset of menopause, homogeneous for age and body mass index (BMI) and without personal history of psychiatric, metabolic or endocrine disorders. Depression and anxiety-related symptoms were assessed with the Zung Self-administered Depression Scale (ZSDS) and the Cornell's Dysthymia Rating Scale (CDRS). The cut-off value predicted by the ZSDS index defined two groups of women (asymptomatic [35.5+/-4.6, n=12] and symptomatic [60.8+/-7.9, n=13]), that were also significantly different according to the CDRS scores (10.6+/-3.4 and 31.5+/-12, respectively, P<0.05). Upon evaluation of the scores relative to the anxiety factor of the CDRS (items 11-15) the symptomatic, but not the asymptomatic, group showed a moderate level of anxiety. The plasma concentrations of several neuroactive steroids were measured, after extraction and HPLC purification, by radioimmunoassay with specific antisera. Only dehydroepiandrosterone and its metabolite 5alpha-androstane-3alpha,17betadiol (3alpha-ADIOL), a positive allosteric modulator of GABA(A) receptors, were significantly (P<0.05 and P<0.005) higher (+110% and +64%, respectively) in the asymptomatic group. A highly significant and negative correlation (r=-0.672, P=0.003) was found between the plasma 3alpha-ADIOL concentrations and the scores of the anxiety factor of the CDRS. These data suggest that endogenous 3alpha-ADIOL modulates the central GABAergic tone and that higher 3alpha-ADIOL concentrations could have a role in preventing the expression of anxiety in the asymptomatic women.

Anxiety↗
PubMed1998

Modulation of GABA(A) receptor function by neuroactive steroids: evidence for heterogeneity of steroid sensitivity of recombinant GABA(A) receptor isoforms.

Neuroactive steroids are potent, selective allosteric modulators of gamma-aminobutyric acid type A (GABA(A)) receptor function in the central nervous system, and may serve as endogenous anxiolytic and analgesic agents. In order to study the influence of subunit subtypes of the GABA(A) receptor on modulation of receptor function by neuroactive steroids, we expressed human recombinant GABA(A) receptors in Xenopus oocytes. GABA-activated membrane current, and the modulatory effects of the endogenous neurosteroid 5alpha-pregnan-3alpha-ol-20-one (allopregnanolone) and the synthetic steroid anesthetic 5alpha-pregnan-3alpha-ol-11,20-dione (alphaxalone) were measured using two-electrode voltage-clamp recording techniques. Allopregnanolone had similar effects to potentiate GABA-activated membrane current in the alpha1beta1gamma2L and alpha1beta2gamma2L receptor isoforms. In contrast, alphaxalone was much more effective as a positive allosteric modulator on the alpha1beta1gamma2L receptor isoform. In the absence of the gamma2L subunit subtype, allopregnanolone had much greater efficacy, but its potency was decreased. Allopregnanolone was much more effective on the alpha1beta1 receptor isoform compared with the alpha1beta2 receptor isoform. The potency for alphaxalone to potentiate the GABA response was not altered in the absence of the gamma2L subunit subtype, although its efficacy was greatly enhanced. Both allopregnanolone and alphaxalone produced nonparallel leftward shifts in the GABA concentration-response relationship in the absence of the gamma2L subunit, decreasing the EC50 concentration of GABA and increasing the maximal response. Only alphaxalone increased the maximal GABA response when the gamma2L subunit subtype was present. The 3beta-pregnane isomers epipregnanolone and isopregnanolone both inhibited the ability of allopregnanolone and alphaxalone to potentiate GABA(A) receptor function. However, the degree of block produced by the 3beta-pregnane steroid isomers was dependent on the type of receptor isoform studied and the neuroactive steroid tested. Isopregnanolone, the 3beta-isomer of allopregnanolone, was significantly more effective as a blocker of potentiation caused by allopregnanolone compared with alphaxalone in all receptor isoforms tested. Epipregnanolone had a greater efficacy as a blocker at the alpha1beta2gamma2L receptor isoform compared with the alpha1beta1gamma2L receptor isoform, and also produced a greater degree of block of potentiation caused by allopregnanolone compared with alphaxalone. Our results support the hypothesis that the heteromeric assembly of different GABA(A) receptor isoforms containing different subunit subtypes results in multiple steroid recognition sites on GABA(A) receptors, which in turn produces distinctly different modulatory interactions between neuroactive steroids acting at the GABA(A) receptor. The alpha and gamma subunit subtypes may have the greatest influence on allopregnanolone modulation of GABA(A) receptor function, whereas the beta and gamma subunit subtypes appear to be most important for the modulatory effects of alphaxalone.

Animals↗
PubMed2006

The changing landscape of protein allostery.

It is becoming increasingly clear that the fundamental capacity to undergo conformational change in response to ligand binding is intrinsic to proteins. This property confers on proteins the ability to be allosterically modulated in order to shift substrate binding affinities, alter enzymatic activity or regulate protein-protein interaction. How this allosteric modulation occurs--the pathways of communication, the shifting of conformational ensembles and the altered molecular dynamics--has received considerable attention during the past two years. Recent progress has helped outline the molecular origins of allostery in proteins as diverse as Hsp70 molecular chaperones and signal integrating proteins, such as WASP. In addition, allosteric properties have been successfully engineered into proteins for drug design or the development of novel biosensors. Methodological advances have provided exciting prospects for new insights and new biological roles of allosteric systems have been uncovered.

Allosteric Regulation↗