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Competitive Antagonist (competitive + antagonist)
Selected AbstractsDiscovery and recognition of purine receptor subtypes on plateletsDRUG DEVELOPMENT RESEARCH, Issue 1-2 2001Susanna M.O. HouraniArticle first published online: 9 MAY 200 Abstract The effects of purines on platelets have been known since the 1960s, when Born demonstrated aggregation induced by ADP and its inhibition by adenosine and by ATP. The inhibition by adenosine is not specific for ADP, and adenosine acts at a separate receptor to stimulate adenylate cyclase, which has an inhibitory effect on platelet function. Studies using selective agonists and antagonists have shown that the platelet receptor is of the A2A subtype and this has been confirmed using A2A knockout mice. The situation with ADP is more complex, and there has been controversy about the number of ADP receptors on platelets. ADP causes shape change, aggregation, mobilisation of calcium from intracellular stores, rapid calcium influx, and inhibition of adenylate cyclase, and the relationship between these is becoming clearer. Two cloned P2 receptors have been detected on platelets, P2X1 and P2Y1, and a third P2Y receptor is thought to exist. The P2X1 receptor is responsible for the rapid calcium influx and can be activated by ATP as well as by ADP, but is likely to be desensitised under normal experimental conditions and its pathophysiological role is uncertain. The P2Y1 receptor is responsible for calcium mobilisation, shape change, and the initiation of aggregation, and these responses are abolished in P2Y1 knockout mice, while the other P2Y receptor is responsible for inhibition of adenylate cyclase and is required for full aggregation. ATP is a competitive antagonist at both these P2Y receptors, while some nucleotide analogues can discriminate between them. Drug Dev. Res. 52:140,149, 2001. © 2001 Wiley-Liss, Inc. [source] Inverse relationship between seizure expression and extrasynaptic NMDAR function following chronic NMDAR inhibitionEPILEPSIA, Issue 2010Suzanne B. Bausch Summary We showed previously that electrographic seizures involving dentate granule cells in organotypic hippocampal slice cultures were dramatically reduced following chronic treatment with the NR2B-selective antagonist, Ro25,6981, but were increased following chronic treatment with the high-affinity competitive antagonist, D(-)-2-amino-5-phosphonopentanoic acid (D-APV). To begin to investigate the potential mechanisms underlying the differential effects of N -methyl- d -aspartate receptor (NMDAR) antagonists on seizures, electrophysiologic experiments were conducted in dentate granule cells in hippocampal slice cultures treated for the entire 17,21 day culture period with vehicle, Ro25,6981 or D-APV. Initial experiments revealed a lack of an association between miniature excitatory postsynaptic current (mEPSC) measures and seizures suggesting that shifts in mEPSC were unlikely to account for the differential effects of D-APV and Ro25,6981 on seizures. However, the amplitude of tonic NMDAR-mediated currents was reduced in cultures treated chronically with D-APV and dramatically enhanced in cultures treated chronically with Ro25,6981. Because tonic NMDAR currents are mediated primarily by extrasynaptic NMDAR, these data show an inverse relationship between changes in extrasynaptic NMDAR function and alterations in seizure expression. [source] Characterization of the Tetanus Toxin Model of Refractory Focal Neocortical Epilepsy in the RatEPILEPSIA, Issue 2 2005Karen E. Nilsen Summary:,Purpose: To characterize in detail a model of focal neocortical epilepsy. Methods: Chronic focal epilepsy was induced by injecting 25,50 ng of tetanus toxin or vehicle alone (controls) into the motor neocortex of rats. EEG activity was recorded from electrodes implanted at the injection site, along with facial muscle electromyographic (EMG) activity and behavioral monitoring intermittently for up to 5 months in some animals. Drug responsiveness was assessed by using the antiepileptic drugs (AEDs) diazepam (DZP) and phenytoin (PHT) delivered systemically, while 1,2,3,4-tetrahydro-6-nitro-2,3-dioxo-benzo[f]quinoxaline-7-sulfonamide (NBQX), a competitive antagonist at AMPA receptors, was administered directly to the brain to investigate the potential benefits of focal drug delivery. Results: Tetanus toxin induced mild behavioral seizures that persisted indefinitely in all animals. EEG spiking activity, occurring up to 80% of the time, correlated with clinical seizures consisting of interrupted behavioral activity, rhythmic bilateral facial twitching, and periods of abrupt motor arrest. Seizures were refractory to systemic administration of DZP and PHT. However, focal delivery of NBQX to the seizure site reversibly reduced EEG and behavioral seizure activity without detectable side effects. Conclusions: This study provides a long-term detailed characterisation of the tetanus toxin model. Spontaneous, almost continuous, well-tolerated seizures occur and persist, resembling those seen in neocortical epilepsy, including cortical myoclonus and epilepsia partialis continua. The seizures appear to be similarly resistant to conventional AEDs. The consistency, frequency, and clinical similarity of the seizures to refractory epilepsy in humans make this an ideal model for investigation of both mechanisms of seizure activity and new therapeutic approaches. [source] Neurotoxicity of channel mutations in heterologously expressed ,7-nicotinic acetylcholine receptorsEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 10 2001Ronald J. Lukas Abstract Nicotinic acetylcholine receptors (nAChR) composed of chick ,7 subunits mutated to threonine at amino acid valine-251 in the putative channel-lining M2 domain were expressed heterologously in several neuron-like and non-neuronal mammalian cell lines. Expression of mutant ,7-nAChR is toxic to neuron-like cells of the human neuroblastoma cell lines SH-SY5Y and IMR-32, but not to several other cell types. Growth in the presence of the ,7-nAChR antagonist methyllycaconitine (MLA) protects against neurotoxicity, as does gradual downregulation of functional, mutant ,7-nAChR in surviving transfected SH-SY5Y cells. Relative to wild-type ,7-nAChR, functional ,7-nAChR mutants show a higher affinity for agonists, slower rates of desensitization, and sensitivity to dihydro-,-erythroidine (DH,E) as an agonist, but they retain sensitivity to MLA as a competitive antagonist. These findings demonstrate that expression of hyperfunctional, mutant forms of Ca2+ -permeable ,7-nAChR is toxic to neuron-like cells. [source] Molecular Library Obtained by Allene Insertion into the Pd,C Bond of Cyclopalladated Complexes: Biological and Pharmacological EvaluationEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 8 2004Claude Sirlin Abstract A minilibrary of cationic N-heterocycles has been prepared and evaluated. The potential for the preparation was a result of the high versatility of palladium-mediated chemistry. The synthesis of the novel molecules was based on intramolecular quaternization of tertiary amine attached allylpalladium complexes. The steric and electronic factors of the reaction are discussed. The structures of the synthesized molecules made them candidates for precise biological and pharmacological evaluations. Of the various N-heterocyclic compounds, 2,2-dimethyl-3-methylenenaphtho[def]quinolizinium showed antibacterial activity at micromolar concentrations. This compound also proved to be a nanomolar competitive antagonist for the channel site of the nicotinic acetylcholine receptor. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source] Hypoxia-Induced Apoptotic Cell Death is Prevented by Oestradiol Via Oestrogen Receptors in the Developing Central Nervous SystemJOURNAL OF NEUROENDOCRINOLOGY, Issue 3 2008V. M. Pozo Devoto The neuroprotective effects of oestrogens have been demonstrated against a variety of insults, including excitotoxicity, oxidative stress and cerebral ischemia under certain conditions. However, the molecular mechanisms underlying oestrogen neuroprotection are still unclear. We aimed to determine whether 17,-oestradiol (E2) administration post-hypoxia (p-hx) was neuroprotective and whether these actions were mediated through oestrogen receptors (ER). For this purpose, 12-embyonic day-old chickens were subjected to acute hypoxia [8% (O2), 60 min], followed by different reoxygenation periods. To test the neuroprotective effect of E2 and its mechanism, embryos were injected 30 min after the end of hypoxia with E2 alone or with ICI 182 780, a competitive antagonist of ER. Cytochrome c (cyt c) release, an indicator of mitochondrial apoptotic pathway, was measured by western blot in optic lobe cytosolic extracts. DNA fragmentation by TUNEL fluorescence and caspase-3 fragmentation by immunofluorescence were detected on optic lobe sections. Acute hypoxia produces a significant increase in cyt c release from mitochondria at 4 h p-hx, followed by an increase in TUNEL positive cells 2 h later (6 h p-hx). Administration of E2 (0.5 mg/egg) produced a significant decrease in cytosolic cyt c levels at 4 h p-hx, in casapse-3 activation and in TUNEL positive cells at 6 h p-hx compared to vehicle treated embryos. In the E2 -ICI 182 780 treated embryos, cyt c release, caspase-3 fragmentation and TUNEL positive cells were similar to the hypoxic embryos, thus suggesting the requirement of an E2,ER interaction for E2 mediated neuroprotective effects. In conclusion, E2 prevents hypoxia-induced cyt c release and posterior cell death and these effects are mediated by oestrogen receptors. [source] Inhaled vs subcutaneous effects of a dual IL-4/IL-13 antagonist in a monkey model of asthmaALLERGY, Issue 1 2010A. Tomkinson Abstract Background:, Pitrakinra is a recombinant protein derived from human interleukin-4 (IL-4) that binds to IL-4R, and acts as a competitive antagonist of IL-4 and IL-13. The studies reported here compare the dose-ranging effects of pitrakinra on allergen-induced airway hyperresponsiveness (AHR) and airway eosinophilia when administered subcutaneously (s.c.) or by inhalation to the Ascaris suum -sensitive cynomolgus monkey for the purpose of elucidating the primary site of pitrakinra's anti-asthmatic action. Methods:, Airway responsiveness to inhaled methacholine and bronchoalveolar lavage cell composition was determined before and after three allergen exposures with a 1-week course of twice-daily (b.i.d.) s.c. or inhaled pitrakinra or placebo treatment. Results:, Treatment with s.c. pitrakinra significantly reduced allergen-induced AHR, with a maximum effect of a 2.8- to 3.8-fold increase in methacholine PC100 relative to control (P < 0.05) observed at b.i.d. s.c. doses of 0.05,0.5 mg/kg. Inhaled pitrakinra also significantly reduced AHR with a similar maximum effect of a 2.8- to 3.2-fold increase in methacholine PC100 relative to control (P < 0.05) at nominal b.i.d. doses of 3,100 mg. The maximal effect on AHR following inhalation was observed at a plasma concentration which exhibited no efficacy via the subcutaneous route. The effect of pitrakinra on lung eosinophilia was not statistically significant following either route of administration, although lung eosinophil count was reduced in all studies relative to control. Conclusion:, Local administration of pitrakinra to the lung is sufficient to inhibit AHR, one of the cardinal features of asthma, indicating the therapeutic potential of inhaled pitrakinra in the treatment of atopic asthma. [source] Pharmacological Mechanisms of Naltrexone and Acamprosate in the Prevention of Relapse in Alcohol DependenceTHE AMERICAN JOURNAL ON ADDICTIONS, Issue 2003John Littleton M.B.B.S., Ph.D. Naltrexone and acamprosate may ultimately prove to be useful additions to pharmacotherapy for alcoholism by reducing relapse. Naltrexone is a relatively selective competitive antagonist at mu-opioid receptors, and this activity may explain its anti-relapse action either because endogenous opioids are involved in the positively reinforcing effects of alcohol and/or because these same transmitters are involved in the conditioned anticipation of these effects. In contrast, the pharmacology of acamprosate is still poorly understood. This is not surprising because it is a small flexible molecule with similarities to several neuro-active amino acids and is used in high doses. All these factors suggest that it may have multiple actions. Currently, the best explanation for the effects of acamprosate seems to be that it inhibits the glutamatergic transmitter system involved in both the negative reinforcing effects of alcohol and the conditioned "pseudo-withdrawal" that may be important in cue-induced relapse. [source] Caffeine inhibition of ionotropic glycine receptorsTHE JOURNAL OF PHYSIOLOGY, Issue 16 2009Lei Duan We found that caffeine is a structural analogue of strychnine and a competitive antagonist at ionotropic glycine receptors (GlyRs). Docking simulations indicate that caffeine and strychnine may bind to similar sites at the GlyR. The R131A GlyR mutation, which reduces strychnine antagonism without suppressing activation by glycine, also reduces caffeine antagonism. GlyR subtypes have differing caffeine sensitivity. Tested against the EC50 of each GlyR subtype, the order of caffeine potency (IC50) is: ,2, (248 ± 32 ,m) ,,3, (255 ± 16 ,m) > ,4, (517 ± 50 ,m) > ,1,(837 ± 132 ,m). However, because the ,3, GlyR is more than 3-fold less sensitive to glycine than any of the other GlyR subtypes, this receptor is most effectively blocked by caffeine. The glycine dose,response curves and the effects of caffeine indicate that amphibian retinal ganglion cells do not express a plethora of GlyR subtypes and are dominated by the ,1, GlyR. Comparing the effects of caffeine on glycinergic spontaneous and evoked IPSCs indicates that evoked release elevates the glycine concentration at some synapses whereas summation elicits evoked IPSCs at other synapses. Caffeine serves to identify the pharmacophore of strychnine and produces near-complete inhibition of glycine receptors at concentrations commonly employed to stimulate ryanodine receptors. [source] Protective targeting of high mobility group box chromosomal protein 1 in a spontaneous arthritis modelARTHRITIS & RHEUMATISM, Issue 10 2010Therese Östberg Objective High mobility group box chromosomal protein 1 (HMGB-1) is a DNA binding nuclear protein that can be released from dying cells and activated myeloid cells. Extracellularly, HMGB-1 promotes inflammation. Clinical and experimental studies demonstrate that HMGB-1 is a pathogenic factor in chronic arthritis. Mice with combined gene deficiency for DNase II and IFNRI spontaneously develop chronic, destructive polyarthritis with many features shared with rheumatoid arthritis. DNase II is needed for macrophage degradation of engulfed DNA. The aim of this study was to evaluate a potential pathogenic role of HMGB-1 in this novel murine model. Methods The course of arthritis, assessed by clinical scoring and histology, was studied in DNase II,/, × IFNRI,/, mice, in comparison with heterozygous and wild-type mice. Synovial HMGB-1 expression was analyzed by immunohistochemistry. Serum levels of HMGB-1 were determined by Western immunoblotting and enzyme-linked immunosorbent assay (ELISA), and anti,HMGB-1 autoantibodies were detected by ELISA. Macrophage activation was studied by immunostaining for intracellular interleukin-1, and HMGB-1. HMGB-1 was targeted with truncated HMGB-1,derived BoxA protein, acting as a competitive antagonist, with intraperitoneal injections every second day for 5 weeks. Results DNase II,/, × IFNRI,/, mice developed symmetric polyarthritis with strong aberrant cytosolic and extracellular HMGB-1 expression in synovial tissue, in contrast to that observed in control animals. Increased serum levels of HMGB-1 and HMGB-1 autoantibodies were recorded in DNase II,/, × IFNRI,/, mice, both prior to and during the establishment of disease. Systemic HMGB-1,specific blockade significantly ameliorated the clinical disease course, and a protective effect on joint destruction was demonstrated by histologic evaluation. Conclusion HMGB-1 is involved in the pathogenesis of this spontaneous polyarthritis, and intervention with an HMGB-1 antagonist can mediate beneficial effects. [source] Noncompetitive antagonism of BIBN4096BS on CGRP-induced responses in human subcutaneous arteriesBRITISH JOURNAL OF PHARMACOLOGY, Issue 8 2004Majid Sheykhzade We investigated the antagonistic effect of 1-piperidinecarboxamide, N -[2-[[5amino-l-[[4-(4-pyridinyl)-l-piperazinyl]carbonyl]pentyl]amino]-1-[(3,5-dibromo-4-hydroxyphenyl)methyl]-2-oxoethyl]-4-(1,4-dihydro-2-oxo-3(2H)-quinazolinyl) (BIBN4096BS) on the calcitonin gene-related peptide (CGRP)-induced responses by using isometric myograph and FURA-2 technique in human subcutaneous arteries removed in association with abdominal surgery. BIBN4096BS, at the concentration of 1 pM, had no significant effect on the CGRP-induced relaxation in these vessels. At the concentration of 10 pM, BIBN4096BS had a competitive antagonistic-like behaviour characterized by parallel rightward shift in the log CGRP concentration-tension curve with no depression of the Emax. At the higher concentrations (0.1 and 1 nM), BIBN4096BS had a concentration-dependent noncompetitive antagonistic effect on the CGRP-induced responses. The efficacy and potency of CGRP was significantly greater in the smaller (lumen diameter ,200 ,m) human subcutaneous arteries compared to the larger ones. The apparent agonist equilibrium dissociation constant, KA, for CGRP1 receptors in the human subcutaneous arteries was approximately 1 nM. Analysis of the relationship between receptor occupancy and response to CGRP indicates that the receptor reserve is relatively small. Using reverse transcriptase-polymerase chain reaction (RT-PCR), the presence of mRNA sequences encoding the calcitonin receptor-like receptor, receptor activity modifying protein (RAMP1, RAMP2, RAMP3) and receptor component protein were demonstrated in human subcutaneous arteries, indicating the presence of CGRP1 -like receptor and the necessary component for the receptor activation. In conclusion, the inhibitory action of BIBN4096BS at the low concentration (10 pM) on the CGRP-tension curve (but not intracellular calcium concentration ([Ca2+]i) resembles what is seen with a reversible competitive antagonist. However, at the higher concentrations (0.1 and 1 nM), BIBN4096BS acts as a selective noncompetitive inhibitor at CGRP1 receptors in human subcutaneous arteries. British Journal of Pharmacology (2004) 143, 1066,1073. doi:10.1038/sj.bjp.0705967 [source] Bradyzide, a potent non-peptide B2 bradykinin receptor antagonist with long-lasting oral activity in animal models of inflammatory hyperalgesiaBRITISH JOURNAL OF PHARMACOLOGY, Issue 1 2000Gillian M Burgess Bradyzide is from a novel class of rodent-selective non-peptide B2 bradykinin antagonists (1-(2-Nitrophenyl)thiosemicarbazides). Bradyzide has high affinity for the rodent B2 receptor, displacing [3H]-bradykinin binding in NG108-15 cells and in Cos-7 cells expressing the rat receptor with KI values of 0.51±0.18 nM (n=3) and 0.89±0.27 nM (n=3), respectively. Bradyzide is a competitive antagonist, inhibiting B2 receptor-induced 45Ca efflux from NG108-15 cells with a pKB of 8.0±0.16 (n=5) and a Schild slope of 1.05. In the rat spinal cord and tail preparation, bradyzide inhibits bradykinin-induced ventral root depolarizations (IC50 value; 1.6±0.05 nM (n=3)). Bradyzide is much less potent at the human than at the rodent B2 receptor, displacing [3H]-bradykinin binding in human fibroblasts and in Cos-7 cells expressing the human B2 receptor with KI values of 393±90 nM (n=3) and 772±144 nM (n=3), respectively. Bradyzide inhibits bradykinin-induced [3H]-inositol trisphosphate (IP3) formation with IC50 values of 11.6±1.4 nM (n=3) at the rat and 2.4±0.3 ,M (n=3) at the human receptor. Bradyzide does not interact with a range of other receptors, including human and rat B1 bradykinin receptors. Bradyzide is orally available and blocks bradykinin-induced hypotension and plasma extravasation. Bradyzide shows long-lasting oral activity in rodent models of inflammatory hyperalgesia, reversing Freund's complete adjuvant (FCA)-induced mechanical hyperalgesia in the rat knee joint (ED50, 0.84 ,mol kg,1; duration of action >4 h). It is equipotent with morphine and diclofenac, and 1000 times more potent than paracetamol, its maximal effect exceeding that of the non-steroidal anti-inflammatory drugs (NSAIDs). Bradyzide does not exhibit tolerance when administered over 6 days. In summary, bradyzide is a potent, orally active, antagonist of the B2 bradykinin receptor, with selectivity for the rodent over the human receptor. British Journal of Pharmacology (2000) 129, 77,86; doi:10.1038/sj.bjp.0703012 [source] NK4 (HGF-antagonist/angiogenesis inhibitor) in cancer biology and therapeuticsCANCER SCIENCE, Issue 4 2003Kunio Matsumoto Invasion and subsequent establishment of metastasis are devastating events for patients with cancer, but past therapeutic approaches have paid relatively little attention to these important issues. Hepatocyte growth factor (HGF) and its receptor, the c-Met tyrosine kinase, play roles in cancer invasion and metastasis in a wide variety of tumor cells. Activation of the c-Met receptor integrates multiple signal transduction pathways involved in cell-cell and cell-matrix interactions, cellular migration, and breakdown of the extracellular scaffold. Paracrine activation of the c-Met receptor by stromal-derived HGF mediates tumor-stromal interactions that facilitate invasion and metastasis. Likewise, aberrant expression of the c-Met receptor and autocrine or mutational activation of c-Met receptor tyrosine kinase are closely associated with the progression of malignant tumors. Based on this background, NK4, a competitive antagonist of HGF-c-Met association was prepared so as to block cancer invasion and metastasis. NK4, an internal fragment of HGF, binds to but does not activate the c-Met receptor, thereby competitively antagonizing the biological activities of HGF. Unexpectedly, NK4 was subsequently shown to be an angiogenesis inhibitor as well, and this angioinhibitory activity is independent of its action as an HGF-antagonist. Importantly, NK4 protein or NK4 gene therapy have been shown to inhibit tumor invasion, metastasis and angiogenesis, effectively converting malignant tumors into benign tumors. Targeting tumor invasion-metastasis and angiogenesis with NK4 seems to have considerable therapeutic potential for cancer patients. (Cancer Sci 2003; 94: 321,327) [source] EFFECTS OF MELATONIN ON BLOOD PRESSURE IN STRESS-INDUCED HYPERTENSION IN RATSCLINICAL AND EXPERIMENTAL PHARMACOLOGY AND PHYSIOLOGY, Issue 10 2008Chun-Mei Xia SUMMARY 1Melatonin, acting through its receptors, is involved in numerous physiological processes, including blood pressure (BP) regulation. In present study, the effect of melatonin inhibition on stress-induced hypertension was investigated. 2The hypertensive model consisted of male Sprague-Dawley rats subjected to electrical foot-shock combined with noise. Microinjection of melatonin (0.1 and 1.0 mmol/L) into the anterior hypothalamic area (AHA) produced a fall in BP in nomortensive rats and stress-induced hypertensive rats (SIHR). Luzindole (10 mmol/L), a competitive antagonist of melatonin MT1 and MT2 receptors, almost completely abolished the depressor effect of melatonin, the MT2 receptor-specific antagonist 4-phenyl-2-propionamidotetralin (10 mmol/L) partially blocked (by approximately 60%) the depressor effect of melatonin, whereas the MT3 receptor-selective antagonist prazosin (10 mmol/L) failed to antagonize the effects of melatonin. 3Brain microdialysis was performed in the AHA and the rostral ventrolateral medulla (RVLM). Melatonin and amino acids in the dialysate samples collected were detected by high-performance liquid chromatography combined with fluorescence detection. The results indicated that melatonin concentrations in the AHA were reduced in SIHR. Microinjection of melatonin into the AHA decreased glutamate release and increased GABA and taurine release in the RVLM, which were paralleled by a decrease in arterial pressure. 4The mRNA expression of MT2 in the AHA of SIHR was higher than that in normotensive control rats, whereas there was no significant difference in MT1 mRNA expressin between the two groups. 5The results of the present study suggest that both a decrease of melatonin and an increase in the MT2 receptor in the AHA are involved in the manifestation of stress-induced hypertension. Both MT1 and MT2 receptors participated in the antihypertensive effect of melatonin in the AHA. The antihypertensive effect of melatonin was related to the decreases in the excitatory amino acid glutamate and increases in the inhibitory amino acids taurine and GABA in the RVLM. [source] Presynaptic source of quantal size variability at GABAergic synapses in rat hippocampal neurons in cultureEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 7 2004Andrea Barberis Abstract The variability of quantal size depends on both presynaptic (profile of the neurotransmitter concentration in the cleft) and postsynaptic (number and gating properties of postsynaptic receptors) factors. Here we have examined the possibility that at nonsaturated synapses in cultured hippocampal neurons, changes in both the transmitter concentration peak and its clearance from the synaptic cleft may influence the variability of spontaneous miniature synaptic GABAergic currents (mIPSCs). We found that, in contrast to the slow-off GABAA receptor antagonist bicuculline, fast-off competitive antagonists such as SR-95103 and TPMPA differentially blocked small and large mIPSCs. In the presence of flurazepam, a drug believed to increase the affinity of GABA for GABAAR, small mIPSCs were enhanced more efficiently than large events. Moreover, the addition of dextran, which increases the viscosity of the extracellular fluid, preferentially increased small mIPSCs with respect to large ones. These observations suggest that changes in the concentration peak and the speed of GABA clearance in the cleft may be an important source of synaptic variability. The study of the correlation between peak amplitude and kinetics of mIPSCs allowed determination of the relative contribution of transmitter peak concentration vs. time of GABA clearance. Small synaptic responses were associated with fast onset and decay kinetics while large amplitude currents were asociated with slow kinetics, indicating a crucial role for GABA synaptic clearance in variability of mIPSCs. By using model simulations we were able to estimate the range of variability of both the concentration and the speed of clearance of the GABA transient in the synaptic cleft. [source] Reducing conditions significantly attenuate the neuroprotective efficacy of competitive, but not other NMDA receptor antagonists in vitroEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 11 2000Ashley K. Pringle Abstract Inappropriate activation of NMDA receptors during a period of cerebral ischaemia is a crucial event in the pathway leading to neuronal degeneration. However, significant research has failed to deliver a clinically active NMDA receptor antagonist, and competitive NMDA antagonists are ineffective in many experimental models of ischaemia. The NMDA receptor itself has a number of modulatory sites which may affect receptor function under ischaemic conditions. Using rat organotypic hippocampal slice cultures we have investigated whether the redox modulatory site affects the neuroprotective efficacy of NMDA receptor antagonists against excitotoxicity and experimental ischaemia (OGD). NMDA toxicity was significantly enhanced in cultures pretreated with a reducing agent. The noncompetitive antagonist MK-801 and a glycine-site blocker were equally neuroprotective in both normal and reduced conditions, but there was a significant rightward shift in the dose,response curves of the competitive antagonists APV and CPP and the uncompetitive antagonist memantine. OGD produced neuronal damage predominantly in the CA1 region, which was prevented by MK-801 and memantine, but not by APV or CPP. Inclusion of an oxidizing agent during the period of OGD had no effect alone, but significantly enhanced the neuroprotective potency of the competitive antagonists. These data clearly demonstrate that chemical reduction of the redox modulatory site of the NMDA receptor decreases the ability of competitive antagonists to block NMDA receptor-mediated neuronal damage, and that the reducing conditions which occur during simulated ischaemia are sufficient to produce a similar effect. This may have important implications for the design of future neuroprotective agents. [source] Muscarinic toxins: tools for the study of the pharmacological and functional properties of muscarinic receptorsJOURNAL OF NEUROCHEMISTRY, Issue 5 2009Denis Servent Abstract Muscarinic receptors mediate metabotropic actions of acetylcholine in the CNS and PNS and autocrine functions of acetylcholine in non-neuronal systems. Because of the lack of highly selective muscarinic ligands, the precise location, functional role, and roles in various diseases of the five muscarinic receptor subtypes remain unclear. Muscarinic toxins isolated from the venom of Dendroaspis snakes have a natural high affinity and selectivity, associated with roles as competitive antagonists, allosteric modulators, and potential agonists. These toxins may therefore be invaluable tools for studying muscarinic receptors. We review data on the structural and pharmacological characterization of the muscarinic toxins, focusing on recent structure,function studies on toxin,receptor interactions. We discuss the potential benefits of using these toxins for investigating muscarinic function in vivo. [source] Novel ,-conotoxins identified by gene sequencing from cone snails native to Hainan, and their sequence diversityJOURNAL OF PEPTIDE SCIENCE, Issue 11 2006Sulan Luo Abstract Conotoxins (CTX) from the venom of marine cone snails (genus Conus) represent large families of proteins, which show a similar precursor organization with surprisingly conserved signal sequence of the precursor peptides, but highly diverse pharmacological activities. By using the conserved sequences found within the genes that encode the ,-conotoxin precursors, a technique based on RT-PCR was used to identify, respectively, two novel peptides (LiC22, LeD2) from the two worm-hunting Conus species Conus lividus, and Conus litteratus, and one novel peptide (TeA21) from the snail-hunting Conus species Conus textile, all native to Hainan in China. The three peptides share an ,4/7 subfamily ,-conotoxins common cysteine pattern (CCX4CX7C, two disulfide bonds), which are competitive antagonists of nicotinic acetylcholine receptor (nAChRs). The cDNA of LiC22N encodes a precursor of 40 residues, including a propeptide of 19 residues and a mature peptide of 21 residues. The cDNA of LeD2N encodes a precursor of 41 residues, including a propeptide of 21 residues and a mature peptide of 16 residues with three additional Gly residues. The cDNA of TeA21N encodes a precursor of 38 residues, including a propeptide of 20 residues and a mature peptide of 17 residues with an additional residue Gly. The additional residue Gly of LeD2N and TeA21N is a prerequisite for the amidation of the preceding C -terminal Cys. All three sequences are processed at the common signal site -X-Arg- immediately before the mature peptide sequences. The properties of the ,4/7 conotoxins known so far were discussed in detail. Phylogenetic analysis of the new conotoxins in the present study and the published homologue of ,4/7 conotoxins from the other Conus species were performed systematically. Patterns of sequence divergence for the three regions of signal, proregion, and mature peptides, both nucleotide acids and residue substitutions in DNA and peptide levels, as well as Cys codon usage were analyzed, which suggest how these separate branches originated. Percent identities of the DNA and amino acid sequences of the signal region exhibited high conservation, whereas the sequences of the mature peptides ranged from almost identical to highly divergent between inter- and intra-species. Notably, the diversity of the proregion was also high, with an intermediate percentage of divergence between that observed in the signal and in the toxin regions. The data presented are new and are of importance, and should attract the interest of researchers in this field. The elucidated cDNAs of these toxins will facilitate a better understanding of the relationship of their structure and function, as well as the process of their evolutionary relationships. Copyright © 2006 European Peptide Society and John Wiley & Sons, Ltd. [source] Antagonistic effects of selective ,1 -adrenoceptor antagonists MDL73005EF and tamsulosin and partial agonists clonidine and tizanidine in rat thoracic aorta and rabbit iliac arteryJOURNAL OF PHARMACY AND PHARMACOLOGY: AN INTERNATI ONAL JOURNAL OF PHARMACEUTICAL SCIENCE, Issue 1 2001Mitsutoshi Satoh The antagonistic effects of MDL73005EF and tamsulosin and partial agonists clonidine and tizanidineat rat thoracic aorta and rabbit iliac artery ,1 -adrenoceptors were investigated in this study. Selective ,1 -adrenoceptor antagonists MDL73005EF and tamsulosin dose-dependently shifted the concentration-response curves for noradrenaline to the right. Schild plots of the results obtained from the inhibition by MDL73005EF (pA2 8.30 ± 0.04) and tamsulosin (pA2 10.51 ± 0.06) of noradrenaline yielded a straight line with a slope of unity in rat thoracic aorta. The slopes of Schild plots obtained from the inhibition by MDL73005EF and tamsulosin of noradrenaline were significantly different from unity in rabbit iliac artery. Schild plots of the results obtained from the inhibition by clonidine and tizanidine of noradrenaline yielded a straight line with a slope of unity in rat thoracic aorta (pA2 7.08 ± 0.04 and 7.32 ± 0.04, respectively). These results suggest that ,1D -adrenoceptors play a significant role in the ,1 -adrenoceptor-agonist-induced contraction of rat thoracic aorta and rabbit iliac artery, and that clonidine and tizanidine interact with the ,1D -adrenoceptor subtype as competitive antagonists in rat thoracic aorta. [source] Evidence of ,1 -adrenoceptor functional changes in omental arteries of patients with end-stage renal diseaseAUTONOMIC & AUTACOID PHARMACOLOGY, Issue 1 2008M. P. Cruz-Domínguez Summary 1,1 -Adrenoceptor (,1 -AR) subtypes were characterized in isolated omental arteries obtained after abdominal surgery in patients with end-stage renal disease (ESRD) or with Diabetes Mellitus type 2 plus ESRD (ESRD-DM). 2 Omental arteries from patients with ESRD and ESRD-DM elicited a significant increase in sensitivity to phenylephrine with a pD2 (,log EC50) of 6.7 and 6.6, respectively, vs. the control (5.8, P < 0.001). 3 Stimulation with phenylephrine was conducted in the presence or absence of selective ,1 -AR competitive antagonists: 5-methylurapidil (,1A -), AH11110A (1-[biphenyl-2-yloxy]-4-imino-4-piperidin-1-yl-butan-2-ol; ,1B -) and BMY7378 (8-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-8-azaspiro [4.5] decane-7,9-dione; ,1D -). The relative abundance of mRNA for all three ,1 -ARs was determined. 4 The maximal contractile responses to phenylephrine were: Emax 1.59 ± 0.17, 1.48 ± 0.08 and 1.55 ± 0.14 g for the ESRD, ESRD-DM and control groups, respectively. 5 Functionally, there was an increment in the affinity for the ,1A -AR antagonist (pA2: control 7.45, ESRD 8.36, ESRD-DM 8.0; P < 0.01), and a reduction in the ,1B -AR antagonist affinity (8.3 for controls, 7.6 for ESRD and 7.3 for ESRD-DM; P < 0.01) associated with renal disease. The affinities for the ,1D -AR antagonist were similar among the studied groups (8.5 for the controls, 8.7 for the ESRD and 8.1 for the ESRD-DM groups). 6 Renal disease increased mRNA expression of ,1B -ARs and reduced both ,1A - and ,1D -ARs subtypes in ESRD and ESRD-DM patients. 7 The results suggest that human omental arteries exposed to chronic uraemia show vascular hypersensitivity to phenylephrine, because of functional ,1 -AR changes. [source] Pharmacological characterization of a novel investigational antimuscarinic drug, fesoterodine, in vitro and in vivoBJU INTERNATIONAL, Issue 8 2008Peter Ney OBJECTIVE To investigate the primary pharmacology of fesoterodine (a novel antimuscarinic drug developed for treating overactive bladder) and SPM 7605 (its active metabolite, considered to be the main pharmacologically active principle of fesoterodine in man) against human muscarinic receptor subtypes, and to investigate in vitro and in vivo functional activity of these agents on the rat bladder compared with existing standard agents. MATERIALS AND METHODS The displacement of radioligand binding by fesoterodine, SPM 7605 and standard agents in membrane preparations of Chinese hamster ovary (CHO) cells expressing the different human muscarinic receptors (M1,M5) was characterized. Agonistic and antagonistic activities were studied using different CHO cell lines stably expressing the human recombinant muscarinic receptor subtypes. The effects of fesoterodine and SPM 7605 on isolated bladder strips contracted by carbachol or electrical field stimulation (EFS) were investigated. In vivo the effects of fesoterodine and SPM 7605 on micturition variables were assessed using continuous cystometry in conscious female Sprague-Dawley rats, and compared to those of oxybutynin and atropine. RESULTS In vitro SPM 7605 potently inhibited radioligand binding at all five human muscarinic receptor subtypes with equal affinity across all five. Fesoterodine had a similar balanced selectivity profile but was less potent than SPM 7605. Both substances were competitive antagonists of cholinergic agonist-stimulated responses in human M1-M5 cell lines and had a similar potency and selectivity profile to the radioligand-binding studies. In rat bladder strips, fesoterodine and SPM 7605 caused a rightward shift of the concentration-response curve for carbachol with no depression of the maximum, and concentration-dependently reduced contractions induced by EFS. The potency of both drugs was similar to that of atropine and oxybutynin. In the presence of the esterase inhibitor neostigmine, the concentration-response curve of fesoterodine was shifted to the right, suggesting that part of the activity was caused by metabolism to SPM 7605 by tissue enzymes. In vivo, low doses (0.01 mg/kg) of fesoterodine and SPM 7605 reduced micturition pressure and increased intercontraction intervals and bladder capacity, but did not affect residual volume. CONCLUSIONS Fesoterodine and its active metabolite, SPM 7605, are nonsubtype selective, competitive antagonists of human muscarinic receptors, but SPM 7605 has greater potency than the parent compound. Pharmacodynamic studies in the rat bladder in vitro confirm the competitive muscarinic antagonist profile of these agents in a native tissue preparation, and in vivo studies in the rat showed effects on bladder function consistent with a muscarinic antagonist profile. [source] KMUP-1 activates BKCa channels in basilar artery myocytes via cyclic nucleotide-dependent protein kinasesBRITISH JOURNAL OF PHARMACOLOGY, Issue 6 2005Bin-Nan Wu This study investigated whether KMUP-1, a synthetic xanthine-based derivative, augments the delayed-rectifier potassium (KDR)- or large-conductance Ca2+ -activated potassium (BKCa) channel activity in rat basilar arteries through protein kinase-dependent and -independent mechanisms. Cerebral smooth muscle cells were enzymatically dissociated from rat basilar arteries. Conventional whole cell, perforated and inside-out patch-clamp electrophysiology was used to monitor K+ - and Ca2+ channel activities. KMUP-1 (1 ,M) had no effect on the KDR current but dramatically enhanced BKCa channel activity. This increased BKCa current activity was abolished by charybdotoxin (100 nM) and iberiotoxin (100 nM). Like KMUP-1, the membrane-permeable analogs of cGMP (8-Br-cGMP) and cAMP (8-Br-cAMP) enhanced the BKCa current. BKCa current activation by KMUP-1 was markedly inhibited by a soluble guanylate cyclase inhibitor (ODQ 10 ,M), an adenylate cyclase inhibitor (SQ 22536 10 ,M), competitive antagonists of cGMP and cAMP (Rp-cGMP, 100 ,M and Rp-cAMP, 100 ,M), and cGMP- and cAMP-dependent protein kinase inhibitors (KT5823, 300 nM and KT5720, 300 nM). Voltage-dependent L-type Ca2+ current was significantly suppressed by KMUP-1 (1 ,M), and nearly abolished by a calcium channel blocker (nifedipine, 1 ,M). In conclusion, KMUP-1 stimulates BKCa currents by enhancing the activity of cGMP-dependent protein kinase, and in part this is due to increasing cAMP-dependent protein kinase. Physiologically, this activation would result in the closure of voltage-dependent calcium channels and the relaxation of cerebral arteries. British Journal of Pharmacology (2005) 146, 862,871. doi:10.1038/sj.bjp.0706387 [source] | ||||||||||||||||