Molecular mechanisms regulating the interactions between the benzodazepines and GABA receptors in the central nervous system.

Using radioreceptor assay techniques to measure the kinetics of GABA and diazepam receptors, a relationship between GABA and benzodiazepine receptors has been firmly established in membranes of brain and neuroblastoma NB2a clonal cell lines. Occupancy of benzodiazepine receptors uncovers a new population of GABA receptors (GABA2 receptors) endowed with high affinity for GABA. Moreover, stimulation of GABA receptors increases the affinity of 1,4-benzodiazepine receptors for 1,4-benzodiazepines. This reciprocal interaction appears to be mediated by an endogenous regulatory protein (for details on this protein see [14 and 29]) which allosterically regulates GABA2 receptors while it competitively interacts with benzodiazepines for their specific binding sites. The rank order of potency of the various 1,4-benzodiazepines to block the action of this protein inhibitor on GABA receptors is related to their capacity to displace 3H-diazepam binding. These data suggest that the interaction between the 1,4-benzodiazepine receptors and the endogenous protein modulator of GABA2 receptors might play a role in the pharmacological action of the 1,4-benzodiazepines.     

Molecular modeling of the GABA/GABA(B) receptor complex

A three-dimensional model of the extracellular domain of the GABA(B) receptor has been built by homology with the leucine/isoleucine/valine-binding protein. The complete putative GABA-binding site in the extracellular domain is described in both the open and closed states. The dynamics of the "Venus flytrap" mechanism has been studied, suggesting that the molecular dipole moments play a key role in GABA binding and receptor activation. Important residues putatively implicated either in ligand binding or in the dynamics of the receptor are pinpointed, thus highlighting target residues for mutagenesis experiments and model validation.     

Interaction of pitrazepin with the GABA/benzodiazepine receptor complex and with glycine receptors

Pitrazepin (3-(piperazinyl-1)-9H-dibenz(c,f)triazolo(4,5-a)azepin) is a new GABAA receptor antagonist reported to antagonize electrophysiological effects of GABA. We have investigated in some detail the interaction of pitrazepin with the GABA/benzodiazepine receptor chloride channel complex. Pitrazepin was found to be a competitive inhibitor of the GABAA receptor which is coupled to [3H]diazepam and [35S]TBPS binding sites; the KI value obtained by Schild analyses was 80 nM. Although pitrazepin interacted weakly with BZ receptors the compound did not affect the chloride gating mechanism (labelled with [35S]TBPS or [3H]avermectin B1a). Further, pitrazepin was a non-selective GABA antagonist since glycine receptors, labelled with [3H]strychnine, were affected at low concentrations (the KI values in rat brain-stem were 71-110 nM).     

Molecular mechanisms of tolerance to and withdrawal of GABA(A) receptor modulators.

Here, we summarize recent data pertaining to the effects of GABA_A receptor modulators on the receptor gene expression in order to elucidate the molecular mechanisms behind tolerance and dependence induced by these drugs. Drug selectivity and intrinsic activity seems to be important to evidence at the molecular level the GABA_A receptor tolerance. On the contrary, we suggested that all drug tested are equally potentially prone to induce dependence. Our results demonstrate that long-lasting exposure of GABA_A receptors to endogenous steroids, benzodiazepines and ethanol, as well as their withdrawal, induce marked effects on receptor structure and function. These results suggest the possible synergic action between endogenous steroids and these drugs in modulating the functional activity of specific neuronal populations. We report here that endogenous steroids may play a crucial role in the action of ethanol on dopaminergic neurons.     

Inhibition of the function of TRPV1-expressing nociceptive sensory neurons by somatostatin 4 receptor agonism: mechanism and therapeutical implications

Release of somatostatin into the circulation from the activated TRPV1-expressing nociceptors revealed by antidromic stimulation of dorsal roots in the rat pinpointed to a novel potential drug target on these nociceptors. The review summarizes the functional, biochemical and pharmacological evidence for a novel somatostatin-mediated counter-regulatory antiinflammatory/antinociceptive "sensocrine" function in rats and guinea-pigs. To identify the somatostatin receptor subtype(s) responsible for this function, experiments were focused on actions of sstR4 receptor agonists as this subtype, similarly to sstR1, is not involved in endocrine regulation. Involvement of somatostatin and the sstR4 was revealed by using pretreatment with somatostatin antibody, depletion of somatostatin with cysteamine, measuring the plasma somatostatin-like immunoreactivity, release from nerves in vitro from isolated trachea, detection of sstR4 receptors in animal and human tissue specimens, using sstR4 gene-deleted mice and investigating in detail effects of a stable peptide analogue of somatostatin (TT-232) and of an ultrapotent non-peptide agonist of sstR4 receptors. Promising antinociceptive, antihyperalgesic effects of these sstR4 agonists were observed in various experimental models of inflammatory and neuropathic conditions which are mediated both by TRPV1-expressing nociceptors and non-neural cells involved in mediation of inflammation. In sstR4 receptor knockout mice an aggravation of inflammation and hyperalgesia was observed.     

Discriminative stimulus properties of CGS 9896: interactions within the GABA/benzodiazepine receptor complex

Male rats were trained to discriminate the stimulus effects of CGS 9896 (30.0 mg/kg) from its vehicle. Once trained, discriminative performance was observed to be dose-responsive in the 3.75-30.0 mg/kg range and analysis of the dose-response curve generated an ED50 of 6.44 mg/kg. Generalization testing with chlordiazepoxide and pentobarbital produced CGS 9896-appropriate responding, whereas administration of the GABA agonists SL 75 102 resulted in 75% (intermediate) generalization to the CGS 9896 discriminative stimulus. Although full antagonism of the CGS 9896 cue was obtained following administration of Ro15-1788 and pentylenetetrazole, the inverse agonist DMCM failed to provide complete antagonism. These results suggest that the discriminative properties of CGS 9896 are consistent with its activity as a benzodiazepine receptor agonist.     

Molecular mechanisms of tolerance to and withdrawal of GABAA receptor modulators

Here, we summarize recent data pertaining to the effects of GABA_A receptor modulators on the receptor gene expression in order to elucidate the molecular mechanisms behind tolerance and dependence induced by these drugs. Drug selectivity and intrinsic activity seems to be important to evidence at the molecular level the GABA_A receptor tolerance. On the contrary, we suggested that all drug tested are equally potentially prone to induce dependence. Our results demonstrate that long-lasting exposure of GABA_A receptors to endogenous steroids, benzodiazepines and ethanol, as well as their withdrawal, induce marked effects on receptor structure and function. These results suggest the possible synergic action between endogenous steroids and these drugs in modulating the functional activity of specific neuronal populations. We report here that endogenous steroids may play a crucial role in the action of ethanol on dopaminergic neurons.     

Functional coupling of gamma-aminobutyric acid (GABA)A and benzodiazepine type II receptors: analysis using purified GABA/benzodiazepine receptor complex from bovine cerebral cortex

Possible functional coupling between gamma-aminobutyric acid (GABA) and benzodiazepine receptors was examined using a purified GABA/benzodiazepine receptor complex. The purified receptor complex was obtained by 1012-S-acetamide adipic hydrazide Sepharose 4B affinity column chromatography, following the solubilization of synaptic membrane from the bovine cerebral cortex with Nonidet P-40. The binding of [3H]GABA to the purified GABA receptor was displaced significantly by muscimol and bicuculline, GABAA receptor agonists and antagonists, respectively, but not by baclofen, a GABAB receptor agonist. On the other hand, the binding of [3H]flunitrazepam to the purified benzodiazepine receptor was found to be displaced by microM ranges of CL 218,872, which is known to be sensitive to the benzodiazepine type II receptor. Furthermore, it was found that the binding of [3H]muscimol to these purified GABAA receptors was enhanced by benzodiazepines, while the binding of [3H]flunitrazepam to these benzodiazepine type II receptors was increased by GABA receptor agonists. These enhancements by GABA agonists and benzodiazepine agonists were found to be blocked by bicuculline and a benzodiazepine receptor antagonist, Ro15-1788, respectively. These results strongly suggest that the purified receptor may consist of GABAA and benzodiazepine type II receptors and possess a functional coupling of these sites, as shown in cerebral synaptic membranes.     

Binding thermodynamics as a tool to investigate the mechanisms of drug-receptor interactions: thermodynamics of cytoplasmic steroid/nuclear receptors in comparison with membrane receptors

Drug-receptor binding thermodynamics has proved to be a valid tool for pharmacological and pharmaceutical characterization of molecular mechanisms of receptor-recognition phenomena. The large number of membrane receptors so far studied has led to the discovery of enthalpy-entropy compensation effects in drug-receptor binding and discrimination between agonists and antagonists by thermodynamic methods. Since a single thermodynamic study on cytoplasmic receptors was known, this paper reports on binding thermodynamics of estradiol, ORG2058, and R1881 bound to estrogen, progesterone, and androgen steroid/nuclear receptors, respectively, as determined by variable-temperature binding constant measurements. The binding at 25 degrees C appears enthalpy/entropy-driven (-53.0 相似文献   

Ectopic expression of the GABA(A) receptor alpha6 subunit in hippocampal pyramidal neurons produces extrasynaptic receptors and an increased tonic inhibition

We generated transgenic (Thy1alpha6) mice in which the GABA(A) receptor alpha6 subunit, whose expression is usually confined to granule cells of cerebellum and cochlear nuclei, is ectopically expressed under the control of the pan-neuronal Thy-1.2 promoter. Strong Thy1alpha6 subunit expression occurs, for example, in deep cerebellar nuclei, layer V iscocortical and hippocampal pyramidal cells and dentate granule cells. Ligand binding and protein biochemistry show that most forebrain alpha6 subunits assemble as alpha6betagamma2-type receptors, and some as alpha1alpha6betagamma2 and alpha3alpha6betagamma2 receptors. Electron microscopic immunogold labeling shows that most Thy1-derived alpha6 immunoreactivity is in the extrasynaptic plasma membrane of dendrites and spines in both layer V isocortical and CA1pyramidal cells. Synaptic immunolabeling is rare. Consistent with the alpha6 subunits' extrasynaptic localization, Thy1alpha6 CA1 pyramidal neurons have a five-fold increased tonic GABA(A) receptor-mediated current compared with wild-type cells; however, the spontaneous IPSC frequency and the mIPSC amplitude in Thy1alpha6 mice decrease 37 and 30%, respectively compared with wild-type. Our results strengthen the idea that GABA(A) receptors containing alpha6 subunits can function as extrasynaptic receptors responsible for tonic inhibition and further suggest that a homeostatic mechanism might operate, whereby increased tonic inhibition causes a compensatory decrease in synaptic GABA(A) receptor responses.     

GABA preincubation of rat brain sections increases [3H]GABA binding to the GABAA receptor and compromises the modulatory interactions

Receptor autoradiography has been employed to investigate the effect of gamma-aminobutyric acid (GABA) preincubation on the interaction of the GABAA receptor with its ligands. [3H]GABA (50 nM) binding to the GABAA receptors is increased by 60% compared to control sections after GABA (100 microM) preincubation. Receptor autoradiography shows that the increase is more pronounced in certain brain areas. The allosteric interactions between the GABA and benzodiazepine recognition sites were also examined. An increase in [3H]GABA (50 nM) binding to rat brain sections by co-incubation with the benzodiazepine, flunitrazepam (FNZ) has been observed autoradiographically. This effect has been quantitated in several brain regions; the overall brain increase in [3H]GABA binding induced by 1 microM FNZ was 20%. The increase in [3H]FNZ (1 nM) binding by co-incubation with GABA has also been observed autoradiographically, and the effect quantitated in four brain regions. The overall brain increase in [3H]FNZ binding induced by 100 microM GABA was 34%. After GABA preincubation these allosteric responses are significantly reduced in size. The increase in the [3H]GABAA binding as a consequence of GABA preincubation appears to reflect an increase in receptor affinity for [3H]GABA with no significant change in the maximum number of binding sites. We suggest that GABA preincubation converts the GABAA receptor to a higher affinity desensitised receptor conformation.     

Complex interaction between quisqualate and kainate receptors as revealed by measurement of GABA release from striatal neurons in primary culture

The effects of non-NMDA receptor agonists were tested on endogenous GABA and [3H]GABA release from highly purified striatal neurons differentiated in primary culture. Kainate (KA), glutamate (Glu) and quisqualate (QA) stimulated [3H]GABA release with EC50S = 85 +/- 20 (n = 6), 6.21 +/- 1.42 (n = 3) and 0.135 +/- 0.035 (n = 3) microM, respectively. KA was the most potent (in term of efficacy) agonist (maximal response at 10 mM: 935 +/- 51% (n = 6) increase over basal release) followed by Glu (at 100 microM: 404 +/- 34% (n = 5) increase) and QA (at 10 microM: 91 +/- 6% (n = 6) increase). Phencyclidine (PCP), which was without effect on QA- and KA-evoked GABA release, inhibited the Glu response by about 50%. QA totally inhibited KA (50 microM)-evoked GABA release with an IC50 = 0.39 +/- 0.11 (n = 4) in a competitive manner (Ki = 0.39 +/- 0.07 microM (n = 3]. Competitive inhibition of the KA response was also observed with the other agonists of the quisqualate receptor, Glu and alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA), suggesting that Glu, QA and AMPA act as partial agonists at the KA receptor. gamma-D-Glutamylaminomethylsulfonic acid (GAMS) also inhibited (IC50 = 2.1 mM) the KA response competitively. However the inhibition by GAMS and QA was not additive. The response to QA was rapidly inactivated (no response after 3 min stimulation) in contrast to the KA-evoked GABA release which remained maximal for at least 3 min. When neurons were first exposed to concanavalin A (con A), a lectin known to inhibit Glu receptor desensitisation on insect muscles, the QA response remained maximal for at least 6 min. Con A greatly enhanced the maximal responses to QA and AMPA and decreased their apparent affinities. The KA-evoked GABA release (but not the veratridine and NMDA effects) was also augmented (no change in the EC50 value) by con A. It is proposed that QA, AMPA and KA act at the same receptor-channel complex (termed G2 receptor) which is desensitised more rapidly when stimulated by QA or AMPA than when stimulated by KA.     

An update on adenosine A2A-dopamine D2 receptor interactions: implications for the function of G protein-coupled receptors

Adenosine A(2A)-dopamine D(2) receptor interactions play a very important role in striatal function. A(2A)-D(2) receptor interactions provide an example of the capabilities of information processing by just two different G protein-coupled receptors. Thus, there is evidence for the coexistence of two reciprocal antagonistic interactions between A(2A) and D(2) receptors in the same neurons, the GABAergic enkephalinergic neurons. An antagonistic A(2A)-D(2) intramembrane receptor interaction, which depends on A(2A)-D(2) receptor heteromerization and G(q/11)-PLC signaling, modulates neuronal excitability and neurotransmitter release. On the other hand, an antagonistic A(2A)-D(2) receptor interaction at the adenylyl-cyclase level, which depends on G(s/olf)- and G(i/o)-type V adenylyl-cyclase signaling, modulates protein phosphorylation and gene expression. Finally, under conditions of upregulation of an activator of G protein signaling (AGS3), such as during chronic treatment with addictive drugs, a synergistic A(2A)-D(2) receptor interaction can also be demonstrated. AGS3 facilitates a synergistic interaction between G(s/olf) - and G(i/o)-coupled receptors on the activation of types II/IV adenylyl cyclase, leading to a paradoxical increase in protein phosphorylation and gene expression upon co-activation of A(2A) and D(2) receptors. The analysis of A(2)-D(2) receptor interactions will have implications for the pathophysiology and treatment of basal ganglia disorders and drug addiction.     

Molecular mechanisms of the potent and stereospecific nicotinic receptor agonist (+)-anatoxin-a

Anatoxin-a (AnTX) was shown to be a highly potent and stereospecific agonist at nicotinic synapses in frog skeletal muscle and Torpedo electric organs. AnTX binds to the nicotinic-acetylcholine receptor with a higher affinity than for acetylcholine (ACh) but does not bind to sites in the receptor-gated ionic channel. (+)AnTX caused receptor desensitization, i.e., the loss of agonist-stimulated binding of histrionicotoxin to an allosteric site with time, at a rate significantly slower than that of ACh. Single channel patch clamp recordings indicated that the conductance of channels activated by (+)AnTX (28 pS) and ACh (27 pS) were similar. The (+)AnTX-activated channels contained rapid closing events, the burst times caused by the toxin were shorter than those caused by ACh but had similar voltage dependencies, and the number of short closures per burst was constant at all potentials with both agonists. The bursts of rapid openings and rapid closures (tau = 0.4 msec) appear to result from repetitive opening and closing of the (+)AnTX-bound receptor-ion channel. It is concluded that the semirigid molecule and secondary amine (+)AnTX is a more potent agonist than ACh or carbamylcholine because of a higher affinity for the receptor. At various concentrations the toxin activates the appearance of channels with the same conductances as ACh-induced channels but with a shorter channel lifetime.     

Molecular interactions of dioxins and DLCs with the ketosteroid receptors: an in silico risk assessment approach

Dioxins and dioxin-like compounds (DLCs) are the ones with poor water solubility and low volatility, resistant to physical, chemical and biological processes, persistent in the environment even under extreme conditions. Due to lipophilic nature, they get adhered to the fatty material and concentrate through biomagnification and bioaccumulation, thereby easily getting incorporated into food chains, paving the way to endocrine disruption via modulation of various human receptors. This in turn leads to certain adverse health effects. In the present study, a total of 100 dioxins and DLCs were taken and their binding pattern was assessed with the ketosteroid receptors, i.e. androgen (hAR), glucocorticoid (hGR), progesterone (hPR) and mineralocorticoid (hMR) in comparison to the corresponding natural steroids and a known endocrine disrupting xenobiotic, Bisphenol A (BPA). Most of the DLCs, particularly those bearing hydroxyl (-OH) group showed considerable affinities with ketosteroid receptors. On comparing D scores of all the dioxins and DLCs against all four receptors, compound 8-hydroxy-3,4-dichlorodibenzofuran(8-OH-DCDF) exhibited least D score of -9.549?kcal mol^?1 against hAR. 3,8-Dihydroxy-2-chlorodibenzofuran(3,8-DiOH-CDF), 4′-hydroxy-2,3,4,5-tetrachlorobiphenyl (4′-OH-TCB) and 4-hydroxy-2,2′,5′-trichlorobiphenyl(4-OH-TCB) also showed comparable molecular interactions with the ketosteroid receptors. These interactions mainly include H-bonding, π–π stacking, hydrophobic, polar and van der Waals’ interactions. In contrast, BPA and some natural ligands tested in this study showed lower binding affinities with these receptors than certain DLCs reported herein, i.e. certain DLCs might be more toxic than the proven toxic agent, BPA. Such studies play a pivotal role in the risk assessment of exposure to dioxins and DLCs on human health.     

Cardiovascular responses produced by 5-hydroxytriptamine:a pharmacological update on the receptors/mechanisms involved and therapeutic implications

The complexity of cardiovascular responses produced by 5-hydroxytryptamine (5-HT, serotonin), including bradycardia or tachycardia, hypotension or hypertension, and vasodilatation or vasoconstriction, has been explained by the capability of this monoamine to interact with different receptors in the central nervous system (CNS), on the autonomic ganglia and postganglionic nerve endings, on vascular smooth muscle and endothelium, and on the cardiac tissue. Depending, among other factors, on the species, the vascular bed under study, and the experimental conditions, these responses are mainly mediated by 5-HT₁, 5-HT₂, 5-HT₃, 5-HT₄, 5-ht_5A/5B, and 5-HT₇ receptors as well as by a tyramine-like action or unidentified mechanisms. It is noteworthy that 5-HT₆ receptors do not seem to be involved in the cardiovascular responses to 5-HT. Regarding heart rate, intravenous (i.v.) administration of 5-HT usually lowers this variable by eliciting a von Bezold-Jarisch-like reflex via 5-HT₃ receptors located on sensory vagal nerve endings in the heart. Other bradycardic mechanisms include cardiac sympatho-inhibition by prejunctional 5-HT_1B/1D receptors and, in the case of the rat, an additional 5-ht_5A/5B receptor component. Moreover, i.v. 5-HT can increase heart rate in different species (after vagotomy) by a variety of mechanisms/receptors including activation of: (1) myocardial 5-HT_2A (rat), 5-HT₃ (dog), 5-HT₄ (pig, human), and 5-HT₇ (cat) receptors; (2) adrenomedullary 5-HT₂ (dog) and prejunctional sympatho-excitatory 5-HT₃ (rabbit) receptors associated with a release of catecholamines; (3) a tyramine-like action mechanism (guinea pig); and (4) unidentified mechanisms (certain lamellibranch and gastropod species). Furthermore, central administration of 5-HT can cause, in general, bradycardia and/or tachycardia mediated by activation of, respectively, 5-HT_1A and 5-HT₂ receptors. On the other hand, the blood pressure response to i.v. administration of 5-HT is usually triphasic and consists of an initial short-lasting vasodepressor response due to a reflex bradycardia (mediated by 5-HT₃ receptors located on vagal afferents, via the von Bezold-Jarisch-like reflex), a middle vasopressor phase, and a late, longer-lasting, vasodepressor response. The vasopressor response is a consequence of vasoconstriction mainly mediated by 5-HT_2A receptors; however, vasoconstriction in the canine saphenous vein and external carotid bed as well as in the porcine cephalic arteries and arteriovenous anastomoses is due to activation of 5-HT_1B receptors. The late vasodepressor response may involve three different mechanisms: (1) direct vasorelaxation by activation of 5-HT₇ receptors located on vascular smooth muscle; (2) inhibition of the vasopressor sympathetic outflow by sympatho-inhibitory 5-HT_1A/1B/1D receptors; and (3) release of endothelium-derived relaxing factor (nitric oxide) by 5-HT_2B and/or 5-HT_1B/1D receptors. Furthermore, central administration of 5-HT can cause both hypotension (mainly mediated by 5-HT_1A receptors) and hypertension (mainly mediated by 5-HT₂ receptors). The increasing availability of new compounds with high affinity and selectivity for the different 5-HT receptor subtypes makes it possible to develop drugs with potential therapeutic usefulness in the treatment of some cardiovascular illnesses including hypertension, migraine, some peripheral vascular diseases, and heart failure.     

Molecular evolution of adrenoceptors and dopamine receptors: implications for the binding of catecholamines

We derived homology models for all human catecholamine-binding GPCRs (CABRs; the alpha-1, alpha-2, and beta-adrenoceptors and the D1-type and D2-type dopamine receptor) using the bovine rhodopsin-11-cis-retinal X-ray structure. Interactions were predicted from the endogenous ligands norepinephrine or dopamine and from the binding site and were used to optimize receptor-ligand interactions. Similar binding modes in the complexes agree with a large "binding core" conserved across the CABRs, that is, D3.32, V(I)3.33, T3.37, S5.42, S(A/C)5.43, S5.46, F6.51, F6.52, and W6.48. Model structures and docking simulations suggest that extracellular loop 2 could provide a common attachment point for the ligands' beta-hydroxyl via a hydrogen bond donated by the main-chain NH group of residue xl2.52. The modeled CABRs and docking modes are in good agreement with published experimental studies. Complementarity between the ligand and the binding site suggests that the bovine rhodopsin structure is a suitable template for modeling agonist-bound CABRs.     

Studies on the mechanisms of action of picrotoxin, quercetin and pregnanolone at the GABA rho 1 receptor

1. The mechanisms of action of antagonists of the gamma-aminobutyric acid C (GABA(C)) receptor picrotoxin, quercetin and pregnanolone were studied. 2. Ionic currents (chloride), mediated through human homomeric GABA rho(1) receptors expressed in Xenopus oocytes, were recorded by two-electrode voltage clamp. 3. Dose-response (D-R) curves and kinetic measurements of GABA rho(1) currents were carried out in the presence or absence of antagonists. Use-dependent actions were also evaluated. 4. Picrotoxin, quercetin and pregnanolone exerted noncompetitive actions. 5. IC(50) values measured at the EC(50) for GABA (1 microM) were as follows: picrotoxin 0.6+/-0.1 microM (Hill coefficient n=1.0+/-0.2); quercetin 4.4+/-0.4 microM (n=1.5+/-0.2); pregnanolone 2.1+/-0.5 microM (n=0.8+/-0.1). 6. These antagonists produced changes only in the slope of the linear current-voltage relationships, which was indicative of voltage-independent effects. 7. The effect of picrotoxin on GABA rho(1) currents was use-dependent, strongly relied on agonist concentration and showed a slow onset and offset. The mechanism was compatible with an allosteric inhibition and receptor activation was a prerequisite for antagonism. 8. The effect of quercetin was use-independent, showed relatively fast onset and offset, and resulted in a slowed time course of the GABA-evoked currents. 9. The effect of pregnanolone was use-independent, presented fast onset and a very slow washout, and did not affect current activation. 10. All the antagonists accelerated the time course of deactivation of the GABA rho(1) currents.     

A proteomic approach to receptor signaling: molecular mechanisms and therapeutic implications derived from discovery of the dopamine D2 receptor signalplex

Recent research in cell signaling has shown that the assembly of G protein coupled receptors into signaling complexes or signalplexes represents the primary mechanism by which receptor-mediated signaling is established and maintained. In this review, we summarize the current state of knowledge regarding protein interactions that comprise the dopamine D2 receptor signalplex within the brain. Studies based on conventional and advanced two-hybrid methodologies, as well as bioinformatic and computational analysis of sequence information from completed genomes have demonstrated interactions between dopamine D2 receptors and a cohort of dopamine receptor interacting proteins (DRIPs). DRIP interactions appear to regulate key aspects of receptor function including the signaling and membrane trafficking of dopamine D2 receptors. Disruptions or modifications of the signalplex, using membrane permeant competing peptide or dominant negative approaches, may represent promising new strategies for the selective targeting of the dopamine D2 receptor in cells and in native tissue. DRIP interactions provide a novel platform for understanding the mechanisms of dopamine receptor signaling, and for the potential development of novel treatments for brain disease.