Evidence that the σ1 receptor is not directly coupled to G proteins
ABSTRACT Sigma (σ) receptors have been implicated in psychosis, cognition, neuroprotection, and locomotion in the central nervous system. The signal transduction mechanisms for σ receptors have not been fully elucidated. In this study, we examined the possible coupling between σ1 receptors and heterotrimeric guanine nucleotide-binding proteins (G proteins) in rodent brain. In σ1 receptor-rich cerebellar membrane preparations, the competitive binding curves of two σ1 agonists, (+)pentazocine and 1S,2R-(−)-cis-N-[2-(3,4-dichlorophenyl)ethyl]-N-methyl-2-(1-pyrrolidinyl)cyclohexylamine (BD737), were unaffected by the addition of 10 μM guanosine-5′-O-(γ-thio)-triphosphate (GTPγS). Neither (+)pentazocine (1–100 μM) nor BD737 (0.01–10 μM) stimulated GTPase activities significantly above basal levels in agonist-stimulated GTPase activity assays in cerebellar membranes. Furthermore, when using the method of agonist-stimulated [35S]GTPγS binding as assessed by autoradiography, we did not observe significant stimulation of [35S]GTPγS binding in rat brain sections by either (+)pentazocine or BD737. The above results demonstrate that the σ1 receptor is not likely be directly coupled to G proteins.
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ABSTRACT: Sigma receptors once considered as a class of opioid receptors are now regarded as unique orphan receptors, distinguished by the ability to bind various pharmacological agents such as the progesterone (steroid), haloperidol (anti-psychotic), and drugs of abuse such as cocaine and methamphetamine. The sigma-1 receptor is a 223 amino acid protein, proposed to have two transmembrane segments. We have developed a scheme for the purification of the guinea pig sigma-1 receptor following overexpression in Escherichia coli as a maltose binding protein (MBP) fusion and extraction with Triton X-100. Affinity chromatography using an amylose column and Ni2+ affinity column was used to purify the sigma-1 receptor. The sigma-1 receptor purified by this method is a 26 kDa polypeptide as assessed by SDS-PAGE, binds sigma ligands with high affinity and can be specifically photoaffinity labeled with the sigma-1 receptor photoprobe, [125I]-iodoazidococaine. Ligand binding using [3H]-(+)-pentazocine indicated that approximately half of the purified protein in Triton X-100 bound to radioligand. The MBP-sigma-1 receptor and the sigma-1 receptor in 0.5% triton were maximally stable for approximately two weeks at -20 degrees C in buffer containing 30% glycerol.Protein Expression and Purification 03/2007; 51(2):283-92. · 1.43 Impact Factor
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ABSTRACT: Sigma receptors have been implicated in a myriad of cellular functions, biological processes and diseases. While the precise biological functions of sigma receptors have not been elucidated, recent work has shed some light on to these enigmatic systems. Sigma receptors have recently been a target of drug development related to psychiatric and neurological disorders. Sigma ligands have also been shown to modulate endothelial cell proliferation and can control angiogenesis which makes them a promising target for oncology applications. Other areas currently being investigated include treatment of gastrointestinal, cardiovascular, endocrine and immune system disorders. Of interest is that the human sigma-1 receptor gene contains a steroid binding component, and several gonadal steroids, including progesterone, testosterone and dehydroepiandrosterone (DHEA), interact with sigma-1 receptors. Of the steroids examined thus far, progesterone binds with the highest affinity to human sigma-1 receptors, with a reported affinity (Ki) as high as 30 nM while the other steroids exhibit lower affinity. For this and other reasons, sigma-1 receptors have been proposed as a link between the central nervous system and the endocrine and reproductive systems. Taken together, the above information highlights an important yet largely unexplored but promising area of research to examine the biological function and therapeutic potential of sigma receptors. This review provides an overview of the current knowledge of these sites with a focus on specific areas where in vivo sigma receptor imaging is currently being investigated.Current pharmaceutical design 02/2007; 13(1):51-72. · 4.41 Impact Factor
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ABSTRACT: Previous research has shown that sigma receptors participate in the actions of cocaine in the body. This has led to investigations of the use of novel agents such as BD1008, BD1067 and YZ-011 as cocaine antagonists. In the present study, three novel analogs (UMB115, UMB116, UMB117), representing composites of these earlier compounds, were evaluated in receptor binding and behavioral studies. In the receptor binding studies, the compounds were shown to have high affinity for sigma receptors and much lower affinities for non-sigma sites. For the behavioral experiments, Swiss Webster mice were pre-treated with saline or one of the novel compounds (0.1-10 mg/kg), followed 15 min later by a convulsive (60 mg/kg), lethal (125 mg/kg), or locomotor stimulatory (10 mg/kg) dose of cocaine. The results showed that UMB115, UMB116 and UMB117 significantly (P<0.05) inhibited cocaine-induced convulsions when administered as a pre-treatment to cocaine. Cocaine-induced lethality was significantly attenuated by UMB116 (P<0.05), but not by UMB115 and UMB117. All three compounds significantly (P<0.05) altered the locomotor stimulatory effects of cocaine, with UMB115 and UMB116 exhibiting attenuating actions. Together, the studies suggest UMB116 as a novel cocaine antagonist.European Journal of Pharmacology 09/2006; 542(1-3):61-8. · 2.59 Impact Factor