Evidence that the σ1 receptor is not directly coupled to G proteins
Neuroscience Program, The George Washington University Medical Center, Washington, DC 20037, USA.European Journal of Pharmacology (Impact Factor: 2.53). 12/2000; 408(2):117-25. DOI: 10.1016/S0014-2999(00)00774-3
Sigma (sigma) receptors have been implicated in psychosis, cognition, neuroprotection, and locomotion in the central nervous system. The signal transduction mechanisms for sigma receptors have not been fully elucidated. In this study, we examined the possible coupling between sigma(1) receptors and heterotrimeric guanine nucleotide-binding proteins (G proteins) in rodent brain. In sigma(1) receptor-rich cerebellar membrane preparations, the competitive binding curves of two sigma(1) 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 microM guanosine-5'-O-(gamma-thio)-triphosphate (GTPgammaS). Neither (+)pentazocine (1-100 microM) nor BD737 (0.01-10 microM) 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]GTPgammaS binding as assessed by autoradiography, we did not observe significant stimulation of [35S]GTPgammaS binding in rat brain sections by either (+)pentazocine or BD737. The above results demonstrate that the sigma(1) receptor is not likely be directly coupled to G proteins.
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ABSTRACT: It has been suggested that neuropeptide Y (NPY) and sigma (sigma) receptor ligands may share a putative NPY/sigma receptor in rat brain. To study whether NPY and sigma receptor ligands have an inverse agonism at this putative NPY/sigma receptor, we measured their effects on G-protein activity in rat brain. Using [35S]GTPgammaS autoradiography, we found that NPY-induced G-protein activation exhibited a discrete distribution pattern in rat brain. G-protein activation in superficial cortical layers and hippocampal CA1-3 region was mainly attributed to Y1 and Y2 receptors, respectively. In the presence of 10 microM sigma-receptor agonist BD737 or 10 microM sigma-receptor antagonist haloperidol, the distribution and density of [35S]GTPgammaS binding stimulated by 10 nM NPY was not significantly altered. In rat cerebellar membranes, NPY stimulated high-affinity GTPase activity in a dose-related manner, with maximal effects of 29% increase over basal level seen at 500 nM. This NPY-elicited GTPase activity was not significantly affected by micromolar concentrations of the sigma-receptor antagonists Dup734 or haloperidol. Since no significant effects by sigma-receptor ligands on NPY-induced G-protein activation were observed, we did not see an inverse agonism of NPY and sigma-receptor ligands at the putative NPY/sigma receptor measured at the level of G-protein activation, suggesting that sigma receptors and NPY receptors do not represent a common population in rat hippocampus and cerebellum. It is also suggested that G-protein activation is not a convergent point for the signal transduction mechanisms of NPY receptors and sigma receptors.Brain Research 06/2001; 901(1-2):208-18. DOI:10.1016/S0006-8993(01)02348-4 · 2.84 Impact Factor
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ABSTRACT: In human neuroblastoma SH-SY5Y cell preparations, sigma(1) receptor agonists (+)-pentazocine and 1S,2R-(-)-cis-N-[2-(3,4-dichlorophenyl)ethyl]-N-methyl-2-(1-pyrrolidinyl)cyclohexylamine (BD737) competed for [3H]haloperidol binding with K(i) values of 67+/-10 and 14+/-10 nM, respectively. (+)-Pentazocine or BD737 up to 10 microM did not affect basal levels of intracellular Ca(2+) concentration ([Ca(2+)](i)) in these cells, but they significantly reduced muscarine-induced [Ca(2+)](i) changes in a dose-related manner. However, the reduction by (+)-pentazocine was not reversed by the sigma(1) receptor antagonist haloperidol. Further studies showed (+)-pentazocine, BD737 and haloperidol could compete for [3H]quinuclidinyl benzilate binding in SH-SY5Y cells with K(i) values of 0.51+/-0.06, 0.32+/-0.07 and 4.4+/-2.3 microM, respectively. Thus, the inhibitory effects on muscarine-induced [Ca(2+)](i) changes by (+)-pentazocine and BD737 in SH-SY5Y cells were likely due to blockade of muscarinic receptors, not due to sigma(1) receptor activation by these ligands.European Journal of Pharmacology 03/2002; 436(1-2):35-45. DOI:10.1016/S0014-2999(01)01606-5 · 2.53 Impact Factor
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ABSTRACT: In a previous study we ascertained the presence of sigma1 and sigma2 recognition sites in the rabbit iris-ciliary body, an ocular structure involved in aqueous humor production and drainage. We characterized the sigma1 sites using the preferential ligand (+)-pentazocine, which caused a significant reduction of intraocular pressure (IOP). In the present study, flunarizine, a calcium channel blocker with a complex pharmacological profile, bound to sigma1 sites expressed in the iris-ciliary body with moderate affinity (K(i) = 68 nM). Unilateral topical flunarizine (0.01-0.1%) caused a dose-related reduction of IOP in ocular normotensive rabbits and in the alpha-chymotrypsin model of ocular hypertension, without altering the IOP of the contralateral eye. This activity was blocked by the sigma1 site antagonist NE-100 [N,N-dipropyl-2-[4-methoxy-3-(2-phenylethoxy)phenyl]ethylamine HCl] which, by itself, had no effect on IOP. Detection of flunarizine in rabbit iris-ciliary body homogenates, after topical instillation, showed that it adequately penetrates the rabbit eye. To investigate mechanisms that may contribute to ocular hypotension induced by sigma1 agonists, we carried out in vitro studies on the isolated rabbit iris-ciliary body. Flunarizine (IC50 = 5. 96 nM) and (+)-pentazocine (IC50 = 3. 81 nM) inhibited [3H]norepinephrine release. Moreover, flunarizine (IC50 = 6.34 nM) and (+)-pentazocine (IC50 = 27.26 nM) also antagonized isoproterenol-induced cAMP accumulation. The action of flunarizine and (+)-pentazocine was sensitive to NE-100 antagonism; however, this latter compound partially prevented their effect on [3H]norepinephrine and cAMP accumulation. These findings indicate that flunarizine and (+)-pentazocine interact with ocular sigma1 sites and may prove effective in the control of ocular hypertension.Journal of Pharmacology and Experimental Therapeutics 01/2003; 303(3):1086-94. DOI:10.1124/jpet.102.040584 · 3.97 Impact Factor
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