• Title/Summary/Keyword: receptor I

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Characteristics of $A_1\;and\;A_2$ Adenosine Receptors upon the Acetylcholine Release in the Rat Hippocampus

  • Kim, Do-Kyung;Lee, Young-Soo;Choi, Bong-Kyu
    • The Korean Journal of Physiology and Pharmacology
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    • v.2 no.1
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    • pp.31-39
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    • 1998
  • As it has been reported that the depolarization induced acetylcholine (ACh) release is modulated by activation of presynaptic $A_1$ adenosine heteroreceptor and various lines of evidence suggest the $A_2$ adenosine receptor is present in the hippocampus. The present study was undertaken to delineate the role of adenosine receptors on the hippocampal ACh release. Slices from the rat hippocampus were equilibrated with $[^3H]choline$ and then the release amount of the labelled product, $[^3H]ACh$, which was evoked by electrical stimulation (rectangular pulses, 3 Hz, 2 ms, 24 mA, $5\;V/cm^{-1}$, 2 min), was measured, and the influence of various adenosine receptor-related agents on the evoked tritium outflow was investigated. And also, the drug-receptor binding assay was performed in order to confirm the presence of $A_1$ and $A_2$ adenosine receptors in the rat hippocampus. N-ethylcarboxamidoadenosine (NECA), a potent adenosine receptor agonist with nearly equal affinity at $A_1$ and $A_2$ adenosine receptors, in concentrations ranging from $1{\sim}30\;{\mu}M$, decreased the electrically-evoked $[^3H]ACh$ release in a concentration-dependent manner without affecting the basal rate of release. And the effect of NECA was significantly inhibited by 8-cyclopentyl-1,3-dipropylxanthine (DPCPX, 2 ${\mu}M$), a selective $A_1$ adenosine receptor antagonist, but was not influenced by 3,7-dimethyl-1-propargylxanthine (DMPX, 5 ${\mu}M$), a specific $A_2$ adenosine receptor antagonist. $N^6-cyclopentyladenosine$ (CPA), a selective $A_1$ adenosine receptor agonist, in doses ranging from 0.1 to 10 ${\mu}M$, reduced evoked $[^3H]ACh$ release in a dose-dependent manner without the change of the basal release. And the effect of CPA was significantly inhibited by 2 ${\mu}M$ DPCPX treatment. 2-P-(2-carboxyethyl)-phenethylamino-5'-N-ethylcarboxamidoadenosine hydrochloride (CGS-21680C), a potent $A_2$ adenosine receptor agonist, in concentrations ranging from 0.1 to 10 ${\mu}M$, did not alter the evoked ACh release. In the drug-receptor binding assay, the binding of $[^3H]2-chloro-N^6-cyclopentyladenosine$ ($[^3H]$CCPA) to the $A_1$ adenosine receptor of rat hippocampal membranes was inhibited by CPA ($K_i$ = 1.22 nM), NECA ($K_i=10.17 nM$) and DPCPX ($K_i=161.86 nM$), but not by CGS-21680C ($K_i=2,380 nM$) and DMPX ($K_i=22,367 nM$). However, the specific binding of $[^3H]CGS-21680C$ to the $A_2$ adenosine receptor was not observed. These results suggest that the $A_1$ adenosine heteroreceptor play an important role in evoked ACh release, but the presence of $A_2$ adenosine receptor is not confirmed in this study.

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Kainate-induced Elevations of Intracellular $Ca^{2+}$ and Extracellular Glutamate are Partially Decreased by NMDA Receptor Antagonists in Cultured Cerebellar Granule Neurons

  • Oh, Seikwan;Shogo-Tokuyama;Patrick P.McCaslin
    • Archives of Pharmacal Research
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    • v.18 no.6
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    • pp.391-395
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    • 1995
  • Several lines of evidence indicate that physiological activity of N-methyl-D-aspartate (NMDA) receptor was blocked by physiological concentration of $Mg^{2+}$ (1.2 mM). However, the activity of NMDA receptor may not be blocked totally with this concentration of $Mg^{2+}$ under elevated membrane potential by kainate. Here, we described the effect of $Mg^{2+}$ on NMDA receptor and how much of NMDA receptor functions could be activated by kainate. Effects of NMDA receptor antagonist on kainate-induced elevation of intracellualr $Ca^{2+}$ levels $([Ca^{2+}]_i)$ and extracellular glutamate level were examined in cultured rat cerebellar granule neurons. kainate-induced elevation of $([Ca^{2+}]_i)$ was not affected by physiological concentration of $Mg^{2+}$. Kainate-induced NMDA-induced elevation was blocked by the same concentration of $MG^{2+}$Kainate-induced elevation of [$([Ca^{2+}]_i)$ was decreased by 32% in the presence of NMDA antagonists, MK-801 and CPP (3-[2-carboxypiperazine-4-yl]propyl-1-phosphonic acid), in $Mg^{2+}$ free buffer. Kainate receptor-activated gluamate release was also decreased (30%) by MK-801 or CPP. These resuts show that certain extent of elevations of intracellular $Ca^{2+}$ and extracellular glutamate by kainate is due to coativation of NMDA receptors.

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IGF-I Exerts an Anti-inflammatory Effect on Skeletal Muscle Cells through Down-regulation of TLR4 Signaling

  • Lee, Won-Jun
    • IMMUNE NETWORK
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    • v.11 no.4
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    • pp.223-226
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    • 2011
  • Although exercise-induced growth factors such as Insulin-like growth factor-I (IGF-I) are known to affect various aspects of physiology in skeletal muscle cells, the molecular mechanism by which IGF-I modulates anti-inflammatory effects in these cells is presently unknown. Here, we showed that IGF-I stimulation suppresses the expression of toll-like receptor 4 (TLR4), a key innate immune receptor. A pharmacological inhibitor study further showed that PI3K/Akt signaling pathway is required for IGF-I-mediated negative regulation of TLR4 expression. Furthermore, IGF-I treatment reduced the expression of various NF-${\kappa}B$-target genes such as TNF-${\alpha}$ and IL-6. Taken together, these findings indicate that the anti-inflammatory effect of exercise may be due, at least in part, to IGF-I-induced suppression of TLR4 and subsequent downregulation of the TLR4-dependent inflammatory signaling pathway.

The Analgesic Effect and the Mechanism of Electroacupuncture on Thermal Hyperalgesia in the Rat Model of Collagenase-induced Arthritis: Mediation by Adrenergic Receptors (Collagenase-induced Arthritis Rat Model에서 Thermal Hyperalgesia에 대한 전침(電鍼)의 진통효과(鎭痛效果) 및 기전연구: Adrenergic Mechanism에 대(對)한 연구(硏究))

  • Seo, Byung-Kwan;Park, Dong-Suk;Baek, Yong-Hyeon
    • Journal of Acupuncture Research
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    • v.28 no.2
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    • pp.57-67
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    • 2011
  • 목적 : Collagenase-induced osteoarthritis(OA) 동물 모델에서 전침의 adrenergic mechanism을 연구하고자 한다. 방법 : Collagenase-induced arthritis(CIA)를 유발하기 위하여 5주령의 male Sprague-Dawley rat의 뒷다리 좌측 무릎 관절에 0.05ml의 4mg/ml collagenase solution을 intra-articular 주입하고, 다시 4일 후에 같은 부위에 같은 농도의 collagenase solution을 intra-articular boosting injection 시행한 뒤, gross, histopathological features 및 biomarker activity 변화를 관찰하였다. 예비실험을 통하여 CIA rat model에서 진통효과를 발휘하는 것으로 확인한, 족삼리(足三里) ($ST_{36}$)에 대한 저빈도 train pulse EA stimulation (2Hz, 0.07 mA, 0.3ms)을 침치료 방법으로 적용하였다. 전침의 진통기전을 확인하기 위하여, ${\alpha}1$-adrenergic antagonist (prazosin, 1 mg/kg, i.p.), ${\alpha}2$-adrenergic receptor antagonist (yohimbine, 2mg/kg, i.p.), ${\alpha}1$-adrenergic receptor agonist(phenylephrine, 2mg/kg, i.p.), ${\alpha}2$-adrenergic receptor agonist(clonidine, $40{\mu}g$/kg, i.p.)을 전침시행 20분 전에 복강 내로 전처치하였다. Tail flick unit(Ugo Basile Model 7360)을 이용하여 열자극에 대한 통증역치를 측정하였다. 결과 : 퇴행성관절염 징후(gross, histopathological features)와 통증역치의 변화가 최대값을 나타내는 CIA 유발 4주차에 저빈도 전침자극(train pulse, 2Hz, 0.07mA, 0.3ms)을 족삼리($ST_{36}$)에 적용하였으며, 족삼리 전침의 진통효과는 ${\alpha}2$-adrenergic receptor antagonist(yohimbine, 2mg/kg, i.p.)전처치에 의해 억제되었으나, ${\alpha}1$-adrenergic antagonist(prazosin, 1 mg/kg, i.p.)전처치에는 억제되지 않았다. 또 ${\alpha}2$-adrenergic receptor agonist(clonidine, $40{\mu}g$/kg, i.p.)의 전처치를 통하여 유의한 synergistic analgesic effect가 관찰되었으나, ${\alpha}1$-adrenergic receptor agonist(phenylephrine, 2mg/kg, i.p.)의 전처치는 전침의 진통효과에 synergistic effect를 미치지 않는 것으로 나타났다. 결론 : 저빈도 족삼리 전침은 CIA로 유발된 염증성 통증에 대하여 진통효과를 발휘하며, 이는 ${\alpha}2$-adrenergic receptor에 의하여 매개되는 것으로 보이며 ${\alpha}1$-adrenergic receptor는 영향을 미치지 않는 것으로 사료된다.

Ginsenosides Inhibit NMDA Receptor-Mediated Epileptic Discharges in Cultured Hippocampal Neurons

  • Kim, Sun-Oh;Rhim, Hye-Whon
    • Archives of Pharmacal Research
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    • v.27 no.5
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    • pp.524-530
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    • 2004
  • Epilepsy or the occurrence of spontaneous recurrent epileptiform discharges (SREDs, seizures) is one of the most common neurological disorders. Shift in the balance of brain between excitatory and inhibitory functions due to different types of structural or functional alterations may cause epileptiform discharges. N-Methyl-D-aspartate (NMDA) receptor dysfunctions have been implicated in modulating seizure activities. Seizures and epilepsy are clearly dependent on elevated intracellular calcium concentration ([C $a^{2+}$]$_{i}$ ) by NMDA receptor activation and can be prevented by NMDA antagonists. This perturbed [C $a^{2+}$]$_{i}$ levels is forerunner of neuronal death. However, therapeutic tools of elevated [C $a^{2+}$]$_{i}$ level during status epilepticus (SE) and SREDs have not been discovered yet. Our previous study showed fast inhibition of ginseng total saponins and ginsenoside R $g_3$ on NMDA receptor-mediated [C $a^{2+}$]$_{i}$ in cultured hippocampal neurons. We, therefore, examined the direct modulation of ginseng on hippocampal neuronal culture model of epilepsy using fura-2-based digital $Ca^{2+}$ imaging and neuronal viability assays. We found that ginseng total saponins and ginsenoside R $g_3$ inhibited $Mg^{2+}$ free-induced increase of [C $a^{2+}$]$_{i}$ and spontaneous [C $a^{2+}$]$_{i}$ oscillations in cultured rat hippocampal neurons. These results suggest that ginseng may playa neuroprotective role in perturbed homeostasis of [C $a^{2+}$]$_{i}$ and neuronal cell death via the inhibition of NMDA receptor-induced SE or SREDs.d SE or SREDs..

Effects of Ginsenosides on $GABA_A$ Receptor Channels Expressed in Xenopus Oocytes

  • Choi, Se-Eun;Choi, Seok;Lee, Jun-Ho;Paul J.Whiting;Lee, Sang-Mok;Nah, Seung-Yeol
    • Archives of Pharmacal Research
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    • v.26 no.1
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    • pp.28-33
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    • 2003
  • Ginsenosides, major active ingredients of Panax ginseng, are known to regulate excitatory ligand-gated ion channel activity such as nicotinic acetylcholine and NMDA receptor channel activity. However, it is not known whether ginsenosides affect inhibitory ligand-gated ion channel activity. We investigated the effect of ginsenosides on human recombinant $GABA_A$ receptor (${\alpha}_1{\beta}_1{\gamma}_{2s}$) channel activity expressed in Xenopus oocytes using a two-electrode voltage-clamp technique. Among the eight individual ginsenosides examined, namely, $Rb_1$, $Rb_2$, Rc, Rd, Re, Rf, $Rg_1$ and $Rg_2$, we found that Rc most potently enhanced the GABA-induced inward peak current ($I_{GABA}$). Ginsenoside Rc alone induced an inward membrane current in certain batches of oocytes expressing the $GABA_A$ receptor. The effect of ginsenoside Rc on $I_{GABA}$ was both dose-dependent and reversible. The half-stimulatory concentration ($EC_{50}$) of ginsenoside Rc was 53.2$\pm$12.3 $\mu$M. Both bicuculline, a $GABA_A$ receptor antagonist, and picrotoxin, a $GABA_A$ channel blocker, blocked the stimulatory effect of ginsenoside Rc on $I_{GABA}$. Niflumic acid (NFA) and 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS), both $CI^{-1}$ channel blockers, attenuated the effect of ginsenoside Rc on I$I_{GABA}$. This study suggests that ginsenosides regulated $GABA_A$ receptor expressed in Xenopus oocytes and implies that this regulation might be one of the pharmacological actions of Panax ginseng.

Effects of Protopanaxatriol-Ginsenoside Metabolites on Rat $N$-Methyl-D-Aspartic Acid Receptor-Mediated Ion Currents

  • Shin, Tae-Joon;Hwang, Sung-Hee;Choi, Sun-Hye;Lee, Byung-Hwan;Kang, Ji-Yeon;Kim, Hyeon-Joong;Zukin, R. Suzanne;Rhim, Hye-Whon;Nah, Seung-Yeol
    • The Korean Journal of Physiology and Pharmacology
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    • v.16 no.2
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    • pp.113-118
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    • 2012
  • Ginsenosides are low molecular weight glycosides found in ginseng that exhibit neuroprotective effects through inhibition of $N$-methyl-D-aspartic acid (NMDA) receptor channel activity. Ginsenosides, like other natural compounds, are metabolized by gastric juices and intestinal microorganisms to produce ginsenoside metabolites. However, little is known about how ginsenoside metabolites regulate NMDA receptor channel activity. In the present study, we investigated the effects of ginsenoside metabolites, such as compound K (CK), protopanaxadiol (PPD), and protopanaxatriol (PPT), on oocytes that heterologously express the rat NMDA receptor. NMDA receptor-mediated ion current ($I_{NMDA}$) was measured using the 2-electrode voltage clamp technique. In oocytes injected with cRNAs encoding NMDA receptor subunits, PPT, but not CK or PPD, reversibly inhibited $I_{NMDA}$ in a concentration-dependent manner. The $IC_{50}$ for PPT on $I_{NMDA}$ was $48.1{\pm}4.6\;{\mu}M$, was non-competitive with NMDA, and was independent of the membrane holding potential. These results demonstrate the possibility that PPT interacts with the NMDA receptor, although not at the NMDA binding site, and that the inhibitory effects of PPT on $I_{NMDA}$ could be related to ginseng-mediated neuroprotection.

Agonistic Activities to the Benzodiazepine Receptor by Extracts of Medicinal Plants(I) -Screening of Some Sedative Plant Extracts- (생약의 Benzodiazepine 수용체 효현활성 검색(I) -수종의 신경안정 생약 추출물에 대한 활성 검색-)

  • Ha, Jeoung-Hee;Park, Yong-Ki;Kang, Byung-Soo;Lee, Dong-Ung
    • Korean Journal of Pharmacognosy
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    • v.30 no.2
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    • pp.211-215
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    • 1999
  • This study was aimed to evaluate an agonistic activity to benzodiazepine receptor of several medicinal plants, which have been used as sedatives in oriental medicine. Methanol extracts of medicinal plants which were used in this study inhibited the binding of $[^3H]Ro15-1788$, a selective benzodiazepine receptor antagonist to benzodiazepine receptor of rat cortices. Inhibitory activity of Cyperus rotundus was observed to be the highest among the tested medicinal plants. Methanol extracts of Cyperus rotundus and Zizypus jujuba inhibited a $[^3H]flunitrazepam$, a selective benzodiazepine receptor agonist, binding to benzodiazepine receptor. GABA significantly enhanced the inhibition of $[3H]flunitrazepam$ binding by Cyperus rotundus and Zizypus jujuba, and these positive GABA shifts supported the strong possibility of agonistic activity to benzodiazepine receptor. From these results, it may be concluded that the substance or substances with neurochemical properties characteristic of a benzodiazepine receptor agonist may be important components and contribute to the sedative property of these medicinal plants.

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Spinal Noradrenergic Modulation and the Role of the Alpha-2 Receptor in the Antinociceptive Effect of Intrathecal Nefopam in the Formalin Test

  • Jeong, Shin Ho;Heo, Bong Ha;Park, Sun Hong;Kim, Woong Mo;Lee, Hyung Gon;Yoon, Myung Ha;Choi, Jeong Il
    • The Korean Journal of Pain
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    • v.27 no.1
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    • pp.23-29
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    • 2014
  • Background: Nefopam has shown an analgesic effect on acute pain including postoperative pain. The reuptake of monoamines including serotonin and noradrenaline has been proposed as the mechanism of the analgesic action of nefopam, but it remains unclear. Although alpha-adrenergic agents are being widely used in the perioperative period, the role of noradrenergic modulation in the analgesic effect of nefopam has not been fully addressed. Methods: Changes in the antinociceptive effect of intrathecal (i.t.) nefopam against formalin-elicited flinching responses were explored in Sprague-Dawley rats pretreated with i.t. 6-hydroxydopamine (6-OHDA), which depletes spinal noradrenaline. In addition, antagonism to the effect of nefopam by prazosin and yohimbine was evaluated to further elucidate the antinociceptive mechanism of i.t. nefopam. Results: Pretreatment with i.t. 6-OHDA alone did not alter the flinching responses in either phase of the formalin test, while it attenuated the antinociceptive effect of i.t. nefopam significantly during phase 1, but not phase 2. The antagonist of the alpha-2 receptor, but not the alpha-1 receptor, reduced partially, but significantly, the antinociceptive effect of i.t. nefopam during phase 1, but not during phase 2. Conclusions: This study demonstrates that spinal noradrenergic modulation plays an important role in the antinociceptive effect of i.t. nefopam against formalin-elicited acute initial pain, but not facilitated pain, and this action involves the spinal alpha-2 but not the alpha-1 receptor.

Insulin-Like Growth Factor-I-Induced Androgen Receptor Activation Is Mediated by the PI3K/Akt Pathway in C2C12 Skeletal Muscle Cells

  • Lee, Won Jun
    • Molecules and Cells
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    • v.28 no.5
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    • pp.495-499
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    • 2009
  • Although insulin-like growth factor-I (IGF-I) and androgen receptor (AR) are well known effectors of skeletal muscle, the molecular mechanism by which signaling pathways integrating AR and IGF-I in skeletal muscle cells has not been previously examined. In this study, the role of PI3K/Akt on IGF-I-induced gene expression and activation of AR in skeletal muscle cells was investigated. C2C12 cells were treated with IGF-I in the absence or presence of inhibitors of PI3K/Akt pathway (LY294002 and Wortmannin). Inhibition of the PI3K/Akt pathway with LY294002 or Wortmannin led to a significant decrease in IGF-I-induced AR phosphorylation and total AR protein expression. Furthermore, IGF-I-induced AR mRNA and skeletal ${\alpha}-actin$ mRNA were blocked by LY294002 or Wortmannin. Confocal images showed that IGF-I-induced AR translocation from cytosol to nucleus was inhibited significantly in response to treatment with LY294002 or Wortmannin. The present results suggest that modulating effect of IGF-I on AR gene expression and activation in C2C12 mouse skeletal muscle cells is mediated at least in part by the PI3K/Akt pathway.