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 919 records · Page 51Linked to original sources
PubMed1988

Glycine and D-serine increase the affinity of N-methyl-D-aspartate sensitive glutamate binding sites in rat brain synaptic membranes.

In previously frozen and extensively washed brain membranes [3H]glutamate binds to a single population of sites characteristic of the NMDA-sensitive glutamate receptor subtype. This binding cannot be displaced by glycine and D-serine, but actually is enhanced by these amino acids in a dose-dependent manner. Glycine and D-serine increase the affinity of glutamate binding without changing the density of binding sites. These results delineate glycine as an allosteric modulator of the recognition site for the NMDA-sensitive glutamate receptor.

Animals↗
PubMed1990

A study of diazepam binding inhibitor (DBI) processing products in human cerebrospinal fluid and in postmortem human brain.

Diazepam binding inhibitor (DBI) is a neuropeptide of 11 kDa molecular size and is unevenly distributed in human and rat brain. It appears to function as a negative allosteric modulator of GABAA receptors. In the present paper, using antibodies directed against several synthetic peptides, which correspond to selective regions of human DBI (DBI 51-70, DBI 37-50, DBI 81-101), it is shown that DBI is processed into at least 6 peptide fragments in both postmortem human brain and in cerebrospinal fluid (CSF). One of these fragments was identified as the synthetic DBI 51-70 fragment (an eikosaneuropeptide, ENP) by combined chromatographic procedures. Immunoblotting analysis of the other fragments, by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (PAGE), revealed an apparent molecular size, ranging from 3-4 kDa for four of them and a larger molecular form of 8 kDa. On the basis of the immunological properties, a tentative amino acid sequence was deduced.

Acetates↗
PubMed1991

Modulation by dopamine of [3H]N-[1-(2-benzo(b)thiophenyl)cyclohexyl]piperidine ([3H]BTCP, a phencyclidine derivative) binding to the dopamine uptake complex.

The modulation by dopamine of the binding of [3H]BTCP to the dopamine (DA) uptake complex was investigated in vivo (in control, reserpine- and L-DOPA-treated mice) and in vitro (on membrane preparations of the striatum of the rat). In both cases increasing doses of DA exerted a non-competitive inhibition of binding of [3H]BTCP, with a Ki value close to its K0.5, determined in competition experiments. Amphetamine and cocaine were also non-competitive inhibitors of the binding of [3H]BTCP, while GBR 12783 was competitive. In the presence of DA, the amount of cocaine required to inhibit the binding of [3H]BTCP was increased both in vitro and in vivo. These results suggest that inhibitors of the uptake of DA, such as BTCP or GBR 12783, modulate allosterically the uptake of DA, by binding to a site different from the DA recognition site. Cocaine, however, seems to share the same recognition site as DA.

Animals↗
PubMed1986

Enhancement of brain calcium antagonist binding by phencyclidine and related compounds.

The abilities of compounds structurally or pharmacologically related to phencyclidine to increase the apparent affinity of the [3H]dihydropyridine calcium channel antagonist [3H]nitrendipine were examined in lysed synaptosomal membrane preparations of rat brain. The p-bromo analog of phencyclidine (1-(1-(4-bromophenyl)cyclohexyl)piperidine) was the most efficacious compound tested in enhancing the apparent affinity of [3H]nitrendipine. The efficacy of this compound was approximately two-fold greater than PCP. The stereoisomers of PCMP (1-(1-phenylcyclohexyl-3-methylpiperidine) were also more efficacious than phencyclidine, although only a small degree of stereoselectivity was observed. Levoxadrol, dexoxadrol and the enantiomers of ketamine did not potentiate [3H]nitrendipine binding. The enantiomers of SKF 10047 (n-allylormetazocine), dextrorphan, levorphanol and the ion channel toxins histrionicotoxin and pumiliotoxin-B also increased the apparent affinity of [3H]nitrendipine, while several local anesthetics and mu-opiate receptor ligands were without effect. These studies suggest that the ability of phencyclidine and structurally related compounds to increase the apparent affinity of [3H]nitrendipine is not mediated through an interaction with phencyclidine receptors, but may represent a unique site for allosteric modulation of neuronal dihydropyridine calcium channel antagonist binding sites.

Anesthetics, Local↗
PubMed1992

Sex differences in sensitivity to pentylenetetrazol but not in GABAA receptor binding.

Female rats have a higher threshold than males for seizures induced by the convulsant pentylenetetrazol, a GABAA receptor-chloride channel complex blocker. No sex difference was observed for the anticonvulsant activities of ethanol or diazepam to protect against pentylenetetrazol seizures. Ovariectomy reduces the pentylenetetrazol seizure threshold of females to that of males. In contrast, females have a lower threshold than males to electroshock seizures. Pentylenetetrazol receptors were compared in males and females and gonadectomized animals by binding of several radioligands to the GABAA receptor complex. No differences were found for these four groups of animals in the binding of [3H]flunitrazepam to the benzodiazepine sites and [35S]t-butyl bicyclophosphorothionate ([35S]TBPS) to the chloride channel/convulsant sites in membrane homogenates, nor for allosteric modulation of binding by GABA, the steroid anesthetic alphaxalone, or the benzodiazepine Ro 5-4864. In tissue section autoradiography, no difference was observed for these same assays nor for the binding of [3H]muscimol in the presence and absence of alphaxalone in several major regions. We conclude that circulating female sex hormones, possibly neurosteroid metabolites of progesterone, known to interact directly with the GABAA receptor complex, are involved in the sex differences in pentylenetetrazol seizure susceptibility.

Anesthetics↗
PubMed1991

A transient osmotic permeabilization method for the introduction of impermeant molecules into functional brain membrane vesicles.

Mouse brain membrane vesicles (microsacs) were transiently permeabilized by hypo-osmotic shock. This permeabilization method resulted in the encapsulation of both [14C]sucrose and exogenous alkaline phosphatase. The efficiency of this method was estimated by [14C]sucrose encapsulation experiments to be approximately 81%. External membrane binding experiments with the lectin [3H]concanavalin A demonstrate that the microsacs were not inverted by permeabilization. Following permeabilization, the functional integrity of a ligand-gated ion channel, the GABAA receptor complex, was investigated. Muscimol-stimulated 36Cl-uptake experiments show that this receptor retains its functional properties including blockade by the receptor antagonist bicuculline and potentiation by the allosteric modulators flunitrazepam and pentobarbital. The osmotic permeabilization technique described here provides several advantages over other permeabilization methods. These advantages include a high trapping efficiency, the encapsulation of not only small solutes but large membrane impermeant compounds such as enzymes and the functional preservation of at least one transmembrane protein. Furthermore, this method does not require specialized equipment and does not result in large, permanent holes in the plasma membrane.

Alkaline Phosphatase↗
PubMed1990

GABAA-receptor expressed from rat brain alpha- and beta-subunit cDNAs displays potentiation by benzodiazepine receptor ligands.

In mammalian brain, the activation of GABAA-receptors is associated with the opening of chloride channels, whose function can be allosterically modulated by drugs, in particular by ligands of the benzodiazepine receptor. Agonistic ligands potentiate while inverse agonists reduce the efficiency of GABA. We have cloned cDNAs encoding alpha 1- and beta 1-subunits of the GABAA-receptor from rat brain. When the corresponding RNAs were co-expressed in Xenopus oocytes. GABA-induced currents were recorded which were inhibited by bicuculline and potentiated by pentobarbital. GABA activated the channel in a weakly cooperative manner. Furthermore, the GABA-response was modulated by benzodiazepine receptor ligands. However, not only various agonists but also the antagonist flumazenil and the inverse agonist DMCM potentiated the GABA-response. Thus, alpha 1- and beta 1-subunits are sufficient to form GABAA-receptors which contain benzodiazepine binding sites, although in a functionally restricted form.

Amino Acid Sequence↗
PubMed1992

Brevetoxins bind to multiple classes of sites in rat brain synaptosomes.

The brevetoxins (PbTx series), neurotoxins produced by the marine dinoflagellate Ptychodiscus brevis, cause dose-dependent activation of the voltage-sensitive sodium channel (VSSC). Saturation binding studies employing adult rat brain synaptosomes suggest the existence of a high affinity/low capacity (HA/LC) and a second, lower affinity/higher capacity (LA/HC) class of binding site. LIGAND analysis of saxitoxin and brevetoxin saturation binding data yields a statistically identical Bmax for the brevetoxin high affinity/low capacity (HA/LC) site (1.9 +/- 0.98 pmol/mg protein) and for saxitoxin (1.72 +/- 0.78 pmol/mg protein; P less than 0.001). The stoichiometry of HA/LC brevetoxin binding and saxitoxin binding approaches 1:1. Covalent modification of synaptosomes with a brevetoxin photoaffinity probe preferentially blocks the HA/LC binding site. Hill plots of saturation binding data yield a coefficient of 1.0 +/- 0.02, demonstrating a lack of cooperativity between brevetoxin binding site classes. Kd and Bmax for toxin binding are independent of membrane polarity, intimating that the observed low affinity/high capacity (LA/HC) binding characteristics are not due to modification of the HA/LC site, and strongly argue for the presence of multiple brevetoxin binding site classes. Half-maximal binding at the LA/HC site, and strongly argue for the presence of multiple brevetoxin binding site classes. Half-maximal binding at the LA/HC site occurs at concentration ranges for which the brevetoxins allosterically modulate binding of other natural toxins to their specific sites.

Animals↗
PubMed1984

In vitro characterization of agonist, antagonist, inverse agonist and agonist/antagonist benzodiazepines.

The efficacy of coupling between the benzodiazepine receptor and chloride channel as well as the coupling to the GABA receptor is differentially affected by different benzodiazepine ligands. In general, the order of efficacy with regard to allosteric effects of benzodiazepine ligands on the chloride channel ([35S]TBPS) and GABA receptor ([3H]muscimol), is: agonist greater than agonist/antagonist greater than partial agonist greater than antagonist; with inverse agonists acting in a manner opposite to the classical benzodiazepine agonists. The chloride ionophore is allosterically modulated both by benzodiazepine and GABA receptors.

Animals↗
PubMed1992

Enzymes as molecular automata: a reflection on some numerical and philosophical aspects of the hypothesis.

Enzymes, by means of their properties of specific recognition and allosteric modulation, are able to integrate many separate processes into systemic units with coherent functions; in a sense, they have to be considered as the true organizers of the cytoplasmic processes. In this respect, the present article describes a simple model, based on binary variables and automata theory, which simulates the basic regulatory performance of the modulated enzyme. The model admits a variety of modifications and improvements; it also suggests some original lines of thought on which to reflect about the organization and collective phenomena of the networks of enzymes. In discussing the connection of this 'molecular automata' hypothesis with other areas of present-day theoretical biology, a fertile panorama of initiatives appear. A special partnership between Information Science (computation) and Biology is developing.

Cell Compartmentation↗
PubMed1994

Molecular and cellular characterization of the GABAA receptor in the rat pancreas.

In the present study, we characterize the molecular structure of the GABAA receptor in pancreas, islets, alpha and beta cells, and in RIN 1046-38 cells. Using the polymerase chain reaction and specific primers for 11 out of the 15 subunits known so far, that may contribute to the composition of the GABAA receptors, we demonstrate that pancreas and its cellular components, as well RIN 1046-38 cells, might contain a GABAA receptor resulting from all the possible combinations in a pentameric configuration of the subtypes alpha 1, alpha 2, alpha 3 of the alpha subunit family, beta 1, beta 2, beta 3 subtypes of the beta subunit family, delta subunit and gamma 2 subtype of the gamma subunit family. The presence of the gamma 2 subunit renders the GABAA receptors potentially sensitive to allosteric modulators.

Animals↗
PubMed1984

Benzodiazepine interactions with GABA receptors.

Benzodiazepines (BZs) produce most, if not all, of their pharmacological actions by specifically enhancing the effects of endogenous and exogenous GABA that are mediated by GABAA receptors. This potentiation consists in an increase of the apparent affinity of GABA for increasing chloride conductance without increase in its efficacy and, on the single chloride channel level, seems to be the result of an increased probability of channel opening events. Recent studies indicate that the BZR is a site on the GABA receptor (GABA-R)-chloride channel complex, through which the gain of the signal transducer function of the latter is allosterically modulated. The unique feature of this drug receptor, which is located on a neurotransmitter receptor-gated ion channel, is its specific interaction with three classes of ligands. Agonists, competitive antagonists and inverse agonists at BZR, respectively increase, do not alter and reduce the gain of the GABA-R function. Compounds have been found that cover a whole spectrum of transition between the two extremes (partial agonists, partial inverse agonists) and for which interesting therapeutic applications can be foreseen.

Afferent Pathways↗
PubMed1984

A resonance Raman study of Ambystoma tigrinum hemoglobins: evidence for intraspecies hemepocket variations.

Using resonance Raman difference spectroscopy, the Raman-active vibrational modes of hemoglobins from adult, neotenic, and larval forms of the salamander, Ambystoma tigrinum have been compared to each other and to human hemoglobin. The local heme environment of the adult and neotenic proteins were identical and differed from that of the larval protein. Differences were observed in modes sensitive to porphyrin pi electron density and axial ligation. Systematic differences were also observed between human and adult salamander hemoglobins particularly in modes sensitive to the heme vinyl environment. The relationship between these environmental differences, oxygen binding affinity, and the effects of allosteric modulators are discussed.

Aging↗
PubMed1990

L-homocysteate stimulates [3H]MK-801 binding to the phencyclidine recognition site and is thus an agonist for the N-methyl-D-aspartate-operated cation channel.

Rat brain synaptosomal membranes that are depleted of endogenous excitatory amino acids cannot bind [(+)-5-methyl-10, 11-dihydro-5H-dibenzo(a,d]cyclohept-5,10-imine maleate] ([3H]MK-801). However, they do so upon the restoration of excitatory amino acid agonists such as L-glutamate. [3H]MK-801 provides a molecular probe which is specific for a binding site located within the ionophore of the N-methyl-D-aspartate-type excitatory amino acid receptor, [3H]MK-801 does not bind to non-N-methyl-D-aspartate excitatory amino acid receptors. Exploiting [3H]MK-801 binding as a quantitative measure of agonist activity with respect to ability of inducing the open channel conformation, the present study demonstrates that L-homocysteate is an agonist almost equivalent to L-glutamate in terms of efficacy (maximal N-methyl-D-aspartate response) as well as potency (EC50). The effect of L-homocysteate was dose-dependent, stereospecific (L-homocysteate greater than DL-homocysteate greater than D-homocysteate), suppressible by the N-methyl-D-aspartate-selective competitive antagonist (+/-)-3(2-carboxy-piperazine-4-yl)propyl-l-phosphonate, and potentiated by the N-methyl-D-aspartate-selective "allosteric" modulator glycine. The demonstrated inactivity of L-homocysteine (and virtually all naturally occurring, non-acidic amino acids) implies that the omega-sulphonic acid moiety is an acceptable substitute for the omega carboxyl group for activating the N-methyl-D-aspartate receptor. While the potency of L-homocysteate at N-methyl-D-aspartate receptors was by a factor of only 1.6 smaller than that of L-glutamate, the affinity of L-homocysteate for kainate-type excitatory amino acid receptors was approximately four-fold lower than that of L-glutamate.(ABSTRACT TRUNCATED AT 250 WORDS)

2-Amino-5-phosphonovalerate↗
PubMed1991

Central-type benzodiazepines inhibit release of alpha-melanocyte-stimulating hormone from the rat hypothalamus.

In a previous work, we have shown that GABA inhibits the release of alpha-melanocyte-stimulating hormone (alpha-melanotropin) from hypothalamic neurons through activation of GABAA receptors [Delbende et al. (1989) Brain Res. 497, 86-93]. Since GABA-gated channel activity can be allosterically modulated by a variety of compounds including benzodiazepines, we have investigated the effect of benzodiazepines in the control of alpha-melanotropin release by the rat basal hypothalamus. This study was conducted in vitro using perifused rat hypothalamic slices and the amount of alpha-melanotropin release was monitored with a sensitive and highly specific radioimmunoassay. Infusion of clonazepam (50 microM), a selective agonist for central-type benzodiazepine binding sites, induced an inhibition of KCl (50 mM)-evoked alpha-melanotropin release. The inhibitory effect of clonazepam was rapid and reversible. Administration of Ro 15-1788 (100 microM), a specific antagonist for central-type benzodiazepine receptors or SR 95531, a GABAA receptor antagonist, completely reversed the inhibitory effect of clonazepam. In addition, Ro 15-1788 and SR 95531 both enhanced the amplitude of the response observed during prolonged KCl infusion on alpha-melanotropin neurons, suggesting the existence of a tonic inhibitory effect of endogenous GABA and/or benzodiazepines in the release of alpha-melanotropin by hypothalamic neurons. To investigate further the effect of benzodiazepines in the regulation of alpha-melanotropin neurons, rats were treated in vivo with clonazepam (5 mg/kg) or the non-selective benzodiazepine receptor agonist diazepam (3 mg/kg). Both compounds caused a significant increase in the content of alpha-melanotropin and beta-endorphin in the rat hypothalamus within 3 h.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1995

Identification of distinct GABAA-receptor subtypes in cholinergic and parvalbumin-positive neurons of the rat and marmoset medial septum-diagonal band complex.

GABAA-receptor heterogeneity is based on a multiplicity of subunits (alpha 1-6, beta 1-4, gamma 1-4, delta, rho 1-2) encoded by distinct genes. Flexibility in GABAergic signal transduction and allosteric modulation is expected to arise from the differential assembly of subunits into receptor subtypes. The aim of the present study was to investigate the potential diversity of receptor subtypes expressed by defined neuron populations, as identified by their neurotransmitter phenotype. To this end we have determined immunohistochemically the subunit repertoire of cholinergic and GABAergic neurons in the basal forebrain of rat and marmoset monkey, focusing on the medial septum-diagonal band complex. Co-localization of the GABAA-receptor subunits alpha 1, alpha 3, beta 2, beta 3, and gamma 2 with markers of cholinergic and GABAergic neurons (choline acetyltransferase and parvalbumin, respectively) was assessed by double- and triple immunofluorescence staining. The results reveal that cholinergic neurons in the rat basal forebrain are typically characterized by the subunit combination alpha 3/beta 3/gamma 2, whereas most of the parvalbumin-positive GABAergic neurons express either the subunit combination alpha 1/beta 2/gamma 2 or the combination alpha 1/alpha 3/beta 2/gamma 2. A similar pattern was observed in marmoset monkey, with GABAA-receptors containing the alpha 1-subunit being associated with parvalbumin-positive cells, but never with cholinergic neurons. Thus, the expression of distinct subunit repertoires by cholinergic and GABAergic neurons points to a functional specialization which is conserved across species. These subunit combinations are likely to correspond to different receptor subtypes, and may reflect the engagement of cholinergic and GABAergic neurons in distinct neuronal circuits in the basal forebrain.

Animals↗
PubMed1994

Promotion of hepatic lipid oxidation and gluconeogenesis as a strategy for appetite control.

There is considerable evidence that hepatic vagal afferents monitor the availability of liver glycogen and glucose metabolites, and that this mechanism participates in appetite regulation. Thus, promotion of gluconeogenesis and liver glycogen storage may enhance satiety. Hepatic lipid oxidation drives gluconeogenesis by positive allosteric modulation of pyruvate carboxylase and fructodiphosphatase. The rate-limiting enzyme for hepatic lipid oxidation, carnitine acyltransferase I, is activated by exogenous carnitine, and inhibited by malonyl coA. The lipogenesis inhibitor (-)-hydroxycitrate--a natural fruit acid found in the Brindall berry--can decrease production of malonyl coA in hepatocytes by potent inhibition of citrate lyase; many studies demonstrate that (-)-hydroxycitrate can reduce body fat accumulation in growing rats, owing in large part to a reduction in appetite. Joint administration of (-)-hydroxycitrate and carnitine should therefore promote hepatic lipid oxidation, gluconeogenesis, and satiety. Thermogenic effects as well as a reduction of the respiratory quotient can also be predicted. If this technique proves clinically useful in weight management, it could be used in conjunction with chromium picolinate and soluble fiber supplements, which appear to aid hunger control at the level of the hypothalamus and terminal ileum, respectively.

Animals↗
PubMed1994

Studies on picrotoxin binding sites of GABAA receptors in rat cortical synaptoneurosomes.

Experiments were performed to characterize [35S]TBPS binding in rat cortical synaptoneurosomes, which have vesicular structures containing both pre- and postsynaptic elements. Scatchard analysis revealed a single component of [35S]TBPS binding sites with KD and Bmax values of 76.1 nM and 1.97 pmoles/mg protein, respectively, under physiological conditions. GABA and muscimol inhibited [35S]TBPS binding in a concentration-dependent manner. IC50 values of these GABAA agonists in displacing synaptoneurosomal [35S]TBPS binding are comparable to previously reported EC50 values of the agonist-stimulated 36Cl- uptake in synaptoneurosomes by these agents. Furthermore, the IC50 values of these GABAA agonists were better correspondence to those determined by [3H]muscimol binding in synaptoneurosomal preparations as reported by Delorey and Brown (3) than those determined in membrane preparations. Although bicuculline increased [35S]TBPS binding in a concentration dependent manner in cortical membranes, it did not affect synaptoneurosomal [35S]TBPS binding. Benzodiazepine agonists and inverse agonists (0.1 to 10 microM) did not show any effects on the binding in the absence of muscimol. However, benzodiazepine agonists potentiated and inverse agonists antagonized muscimol-induced inhibition of synaptoneurosomal [35S]TBPS binding. In addition, an anesthetic steroid, THDOC, and pentobarbital inhibited synaptoneurosomal [35S]TBPS binding in a concentration dependent manner. These results suggest that allosteric modulation of [35S]TBPS binding by various ligands which interact with GABAA supramolecular complexes remain intact in synaptoneurosomes. It appears that this preparation is useful for investigating correlation between functional 36Cl- uptake and individual binding studies of each of the GABAA receptor complex.

Animals↗