• The Korean Journal of Physiology and Pharmacology
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• v.14 no.5
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• pp.299-304
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• 2010

Losartan is a selective angiotensin II (Ang II) type 1 ($AT_1$) receptor antagonist which inhibits vascular smooth muscle cells (VSMCs) contraction and proliferation. We hypothesized that losartan may prevent cell proliferation by activating AMP-activated protein kinase (AMPK) in VSMCs. VSMCs were treated with various concentrations of losartan. AMPK activation was measured by Western blot analysis and cell proliferation was measured by MTT assay and flowcytometry. Losartan dose- and time-dependently increased the phosphorylation of AMPK and its downstream target, acetyl-CoA carboxylase (ACC) in VSMCs. Losartan also significantly decreased the Ang II- or 15% FBS-induced VSMC proliferation by inhibiting the expression of cell cycle associated proteins, such as p-Rb, cyclin D, and cyclin E. Compound C, a specific inhibitor of AMPK, or AMPK siRNA blocked the losartan-induced inhibition of cell proliferation and the $G_0/G_1$ cell cycle arrest. These data suggest that losartan-induced AMPK activation might attenuate Ang II-induced VSMC proliferation through the inhibition of cell cycle progression.

• Proceedings of the Korean Society of Applied Pharmacology
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• 2000.04a
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• pp.17-19
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• 2000

Heterotrimeric G Proteins transduce ligand binding to a wide variety of seven transmembrane cell surface receptors into intracellular signals. The currently accepted model for the activation of G protein suggests that ligand-activated receptor accelerates GDP-GTP exchange reactions on the ${\alpha}$ subunit of the heterotrimeric G protein. At least seventeen distinct isoforms of the G${\alpha}$ subunit protein have been identified in mammalian organisms. Among them, the G${\alpha}$q family consists of five members whose ${\alpha}$ subunits show different expression patterns. G${\alpha}$q and G${\alpha}$11 seem to be almost ubiquitously expressed, whereas G${\alpha}$14 is predominantly expressed in spleen, lung, kidney and testis. G${\alpha}$16 and its murine counterpart G${\alpha}$15 are expressed in hematopoietic cells and has been shown to couple a wide variety of receptors to phosphoinositide-specific phospholipase C activity. Beta-isoforms of phospholipase C were shown to be activated by all members of G${\alpha}$q family, i.e., G${\alpha}$q, G${\alpha}$11, G${\alpha}$l4 and G${\alpha}$16 subunits either in reconstitution system. or in experiments using cDNA transfection with intact Cos-7 cells.

• Journal of Life Science
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• v.31 no.7
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• pp.662-670
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• 2021

Interstitial cells of Cajal (ICCs) are the pacemaking cells in the gastrointestinal (GI) muscles that generate the rhythmic oscillation in membrane potentials known as slow waves. In the present study, we investigated the effects of mirtazapine, a noradrenergic and serotonergic antidepressant, on pacemaking potential in cultured ICCs from the murine small intestine. The whole-cell patch-clamp configuration was used to record pacemaker potential in cultured ICCs. Mirtazapine induced pacemaker potential depolarizations in a concentration-dependent manner in the current clamp mode. Y25130 (a 5-HT3 receptor antagonist), RS39604 (a 5-HT4 receptor antagonist), and SB269970 (a 5-HT7 receptor antagonist) had no effects on mirtazapine-induced pacemaker potential depolarizations. Also, methoctramine, a muscarinic M₂ receptor antagonist, had no effect on mirtazapine-induced pacemaker potential depolarizations, whereas 4-diphenylacetoxy-N-methyl-piperidine methiodide (4-DAMP), a muscarinic M₃ receptor antagonist, inhibited the depolarizations. When guanosine 5'-[β-thio] diphosphate (GDP-β-S; 1 mM) was in the pipette solution, mirtazapine-induced pacemaker potential depolarization was blocked. When an external Ca²⁺ free solution or thapsigargin, a Ca²⁺-ATPase inhibitor of the endoplasmic reticulum, was applied, the generation of pacemaker potentials disappeared, and under these conditions, mirtazapine induced pacemaker potential depolarizations. In addition, protein kinase C (PKC) inhibitor, calphostin C, and chelerythrine inhibited mirtazapine-induced pacemaker potential depolarizations. These results suggest that mirtazapine regulates pacemaker potentials through muscarinic M₃ receptor activation via a G protein-dependent and an external or internal Ca²⁺-independent PKC pathway in the ICCs. Therefore, mirtazapine can control GI motility through ICCs.

• The Korean Journal of Physiology and Pharmacology
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• v.6 no.2
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• pp.63-70
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• 2002

Cholinergic modulation of GABAergic spontaneous miniature inhibitory postsynaptic currents (mIPSCs) by the activation of muscarine receptors was investigated in mechanically dissociated rat nucleus basalis of the Meynert neurons using the conventional whole-cell patch recording configuration. Muscarine $(10{\mu}M)$ reversibly and concentration-dependently decreased mIPSC frequency without affecting the current amplitude distribution. Muscarine action on GABAergic mIPSCs was completely blocked by $1{\mu}M$ methoctramine, a selective $M_2$ receptor antagonist, but not by $1{\mu}M$ pirenzepine, a selective $M_1$ receptor antagonist. NEM $(10{\mu}M),$ a G-protein uncoupler, attenuated the inhibitory action of muscarine on GABAergic mIPSC frequency. Muscarine still could decrease GABAergic mIPSC frequency even in the $Ca^{2+}-free$ external solution. However, the inhibitory action of muscarine on GABAergic mIPSCs was completely occluded in the presence of forskolin. The results suggest that muscarine acts presynaptically and reduces the probability of spontaneous GABA release, and that such muscarine-induced inhibitory action seems to be mediated by G-protein-coupled $M_2$ receptors, via the reduction of cAMP production. Accordingly, $M_2$ receptor-mediated disinhibition of nBM neurons might play one of important roles in the regulation of cholinergic outputs from nBM neurons as well as the excitability of nBM neurons themselves.

• The Korean Journal of Physiology and Pharmacology
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• v.10 no.5
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• pp.255-261
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• 2006

Melittin-induced nociceptive responses are mediated by selective activation of capsaicin-sensitive primary afferent fibers and are modulated by excitatory amino acid receptor, cyclooxygenase, protein kinase C and serotonin receptor. The present study was undertaken to investigate the peripheral and spinal actions of voltage-gated calcium channel antagonists on melittin-induced nociceptive responses. Changes in mechanical threshold and number of flinchings were measured after intraplantar (i.pl.) injection of melittin $(30\;{\mu}g/paw)$ into mid-plantar area of hindpaw. L-type calcium channel antagonists, verapamil [intrathecal (i.t.), 6 or $12\;{\mu}g$; i.pl.,100 & $200\;{\mu}g$; i.p., 10 or 30 mg], N-type calcium channel blocker, ${\omega}-conotoxin$ GVIA (i.t., 0.1 or $0.5\;{\mu}g$; i.pl., $5\;{\mu}g$) and P-type calcium channel antagonist, ${\omega}-agatoxin$ IVA (i.t., $0.5\;{\mu}g$; i.pl., $5\;{\mu}g$) were administered 20 min before or 60 min after i.pl. injection of melittin. Intraplantar pre-treatment and i.t. pre- or post-treatment of verapamil and ${\omega}-conotoxin$ GVIA dose-dependently attenuated the reduction of mechanical threshold, and melittin-induced flinchings were inhibited by i.pl. or i.t. pre-treatment of both antagonists. P-type calcium channel blocker, ${\omega}-agatoxin$ IVA, had significant inhibitory action on flinching behaviors, but had a limited effect on melittin-induced decrease in mechanical threshold. These experimental findings suggest that verapamil and ${\omega}-conotoxin$ GVIA can inhibit the development and maintenance of melittin-induced nociceptive responses.

• YAKHAK HOEJI
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• v.59 no.5
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• pp.207-214
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• 2015

P2Y receptors, a type of P2 receptor family, are G-protein coupled receptors and 8 subtypes have been characterized ($P2Y_1$, $P2Y_2$, $P2Y_4$, $P2Y_6$, $P2Y_{11-14}$). Recently, several studies have shed light on the role of P2Y receptors in bone biology. Among them, little is known on the role of $P2Y_6$ receptor on osteoclast differentiation. Thus, we investigated the role of $P2Y_6$ receptor on osteoclastogenesis using $P2Y_6$ receptor selective antagonist, MRS 2578. When osteoblasts and bone marrow cells were co-cultured in the presence of $VitD_3$ and $PGE_2$, $P2Y_6$ antagonist increased the formation of TRAP positive osteoclasts. To elucidate the target cells of $P2Y_6$ antagonist, we first checked the effect of MRS 2578 on osteoblasts. Treatment of MRS 2578 did not affect OPG : RANKL mRNA ratio in osteoblasts. Next, we checked the effects of $P2Y_6$ antagonist on osteoclast precursors using mouse bone marrow macrophages (BMMs). Addition of MRS 2578 increased the number of osteoclasts in RANKL-treated BMMs. Although $P2Y_6$ antagonist had no effect on RANKL-induced NFATc1, c-Fos and MafB expression levels, it significantly stimulated RANKL-induced Blimp1 mRNA expression in BMMs. Taken together, these data indicate that $P2Y_6$ antagonist increases osteoclast formation by upregulation of Blimp1 expression.

• International Journal of Oral Biology
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• v.42 no.1
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• pp.1-8
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• 2017

In the present study, we investigated the role of peripheral ionotropic receptors in artemin-induced thermal hyperalgesia in the orofacial area. Male Sprague-Dawley rats weighting 230 to 280 g were used in the study. Under anesthesia, a polyethylene tube was implanted in the subcutaneous area of the vibrissa pad, which enabled drug-injection. After subcutaneous injection of artemin, changes in air-puff thresholds and head withdrawal latency time were evaluated. Subcutaneous injection of artemin (0.5 or $1{\mu}g$) produced significant thermal hyperalgesia in a dose-dependent manner. However, subcutaneous injection of artemin showed no effect on air-puff thresholds. IRTX ($4{\mu}g$), a TRPV1 receptor antagonist, D-AP5 (40 or $80{\mu}g$), an NMDA receptor antagonist, or NBQX (20 or $40{\mu}g$), an AMPA receptor antagonist, was injected subcutaneously 10 min prior to the artemin injection. Pretreatment with IRTX and D-AP5 significantly inhibited the artemin-induced thermal hyperalgesia. In contrast, pretreatment with both doses of NBQX showed no effect on artemin-induced thermal hyperalgesia. Moreover, pretreatment with H-89, a PKA inhibitor, and chelerythrine, a PKC inhibitor, decreased the artemin-induced thermal hyperalgesia. These results suggested that artemin-induced thermal hyperalgesia is mediated by the sensitized peripheral TRPV1 and NMDA receptor via activation of protein kinases.

• Biomolecules & Therapeutics
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• v.7 no.1
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• pp.1-6
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• 1999

Effects of Panax ginseng on the morphine toxicity were studied in relation to its effects on the opioid receptor-G protein interactions. Morphine treatments (3 days) reduced the body weight increment rate and the weight of the thymus and spleen. These changes were usually recovered by the concomitant administration of ginseng total saponin (GTS) but occasionally further deteriorated. This discrepancy was studied in relation to the opioid receptor coupling to G protein, that is, the effects of morphine and GTS on the opioid receptors were studied using the antagonist-agonist competitive binding studies. When GTS recovered the morphine toxicity, morphine shifted the striatal $\delta$ receptors to slightly higher affinity state, and this was partly recovered by the GTS treatment. However, morphine did not have any effect on the affinity state of $\delta$ receptor from NG108-15 cells, suggesting that additional factors were needed for the modulation of the affinity states of $\delta$ receptor. Effects of morphine and GTS on $\mu$ receptor were complicate and variable, and we could not reach a clear conclusion. The morphine toxicity might accompany complicate biological involvements, and the modulation of the affinity states of the opioid receptors might explain a part of the effects of GTS on the morphine toxicity.

• Molecules and Cells
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• v.25 no.1
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• pp.91-98
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• 2008

The Glu/$Asp^{7.32}$ residue in extracellular loop 3 of the mammalian type-I gonadotropin-releasing hormone receptor (GnRHR) interacts with $Arg^8$ of GnRH-I, conferring preferential ligand selectivity for GnRH-I over GnRH-II. Previously, we demonstrated that the residues (Ser and Pro) flanking Glu/$Asp^{7.32}$ also play a role in the differential agonist selectivity of mammalian and non-mammalian GnRHRs. In this study, we examined the differential antagonist selectivity of wild type and mutant GnRHRs in which the Ser and Pro residues were changed. Cetrorelix, a GnRH-I antagonist, and Trptorelix-2, a GnRH-II antagonist, exhibited high selectivity for mammalian type-I and non-mammalian GnRHRs, respectively. The inhibitory activities of the antagonists were dependent on agonist concentration and subtype. Rat GnRHR in which the Ser-Glu-Pro (SEP) motif was changed to Pro-Glu-Val (PEV) or Pro-Glu-Ser (PES) had increased sensitivity to Trptorelix-2 but decreased sensitivity to Cetrorelix. Mutant bullfrog GnRHR-1 with the SEP motif had the reverse antagonist selectivity, with reduced sensitivity to Trptorelix-2 but increased sensitivity to Cetrorelix. These findings indicate that the residues flanking $Glu^{7.32}$ are important for antagonist as well as agonist selectivity.

• BMB Reports
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• v.31 no.5
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• pp.515-518
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• 1998

Adhesive interaction of the platelet glycoprotien IIb-IIIa (GP IIb-IIIa) with a plasma protein, such as fibrinogen, plays an important role in thrombosis and hemostasis. The specific sequence Arg-Gly-Asp (RGD) is critical for the binding of fibrinogen to platelet. To examine and characterize the GP IIb-IIIa antagonist from natural sources, we have developed a simple enzyme-linked immunosorbant assay (ELISA) system. The GP IIb-IIIa complex was purified to homogeneity from platelet Iysates by the combination of two affinity chromatographic methods using the synthetic RGD peptide (GRGDSPK)-immobilized Sepharose and wheat germ lectin-Sepharose. The synthetic peptide GRGDSP inhibits GP IIb-IIIa binding to immobilized fibrinogen with an $IC_{50}$ of $1.5\;{\mu}M$. Venoms of three different snake species and a Korean scolopendra extract have strong antagonistic activities for the binding of human fibrinogen to the platelet GP IIb-IIIa complex. The $IC_{50}$ values of the snake venom s and scolopendra were in the range of $5.5\;{\mu}g$ to $60\;{\mu}g$. These results provide meaningful information for developing antiplatelet agents.