• International Journal of Oral Biology
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• v.37 no.1
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• pp.1-7
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• 2012

Opioid receptors have been pharmacologically classified as ${\mu}$, ${\delta}$, ${\kappa}$ and ${\varepsilon}$. We have recently reported that the antinociceptive effect of morphine (a ${\mu}$-opioid receptor agonist), but not that of ${\beta}$-endorphin (a novel ${\mu}/{\varepsilon}$-opioid receptor agonist), is attenuated by whole body irradiation (WBI). It is unclear at present whether WBI has differential effects on the antinociceptive effects of ${\mu}-$, ${\delta}-$, ${\kappa}-$ and ${\varepsilon}$-opioid receptor agonists. In our current experiments, male ICR mice were exposed to WBI (5Gy) from a $^{60}Co$ gamma-source and the antinociceptive effects of opioid receptor agonists were assessed two hours later using the hot water ($52^{\circ}C$) tail-immersion test. Morphine and $D-Ala^2$, $N-Me-Phe^4$, Gly-olenkephalin (DAMGO), [$D-Pen^2-D-Pen^5$] enkephalin (DPDPE), trans-3,4-Dichloro-N-methyl-N-[2-(1-pyrrolidinyl)-cyclohexyl]-benzeneacetamide (U50,488H), and ${\beta}$-endorphin were tested as agonists for ${\mu}$, ${\delta}$, ${\kappa}$, and ${\varepsilon}$-opioid receptors, respectively. WBI significantly attenuated the antinociceptive effects of morphine and DAMGO, but increased those of ${\beta}$-endorphin. The antinociceptive effects of DPDPE and U50,488H were not affected by WBI. In addition, to more preciously understand the differential effects of WBI on ${\mu}-$ and ${\varepsilon}$-opioid receptor agonists, we assessed pretreatment effects of ${\beta}$-funaltrexamine (${\beta}$-FNA, a ${\mu}$-opioid receptor antagonist) or ${\beta}$-$endorphin_{1-27}$ (${\beta}$-$EP_{1-27}$, an ${\varepsilon}$-opioid receptor antagonist), and found that pretreatment with ${\beta}$-FNA significantly attenuated the antinociceptive effects of morphine and ${\beta}$-endorphin by WBI. ${\beta}$-$EP_{1-27}$ significantly reversed the attenuation of morphine by WBI and significantly attenuated the increased effects of ${\beta}$-endorphin by WBI. The results demonstrate differential sensitivities of opioid receptors to WBI, especially for ${\mu}-$ and ${\varepsilon}$-opioid receptors.

• The Korean Journal of Physiology and Pharmacology
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• v.8 no.3
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• pp.153-159
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• 2004

The interstitial cells of Cajal (ICCs) are the pacemaker cells in gastrointestinal tract and generate electrical rhythmicity in gastrointestinal muscles. Therefore, ICC may be modulated by endogenous agents such as neurotransmitter, hormones, and prostaglandins (PGs). In the present study, we investigated the effects of prostaglandins, especially $PGE_2$, on pacemaker currents in cultured ICCs from murine small intestine by using whole-cell patch clamp techniques. ICCs generated spontaneous slow waves under voltage-clamp conditions and showed a mean amplitude of $-452{\pm}39\;pA$ and frequency of $18{\pm}2$ cycles/min (n=6). Treatments of the cells with $PGE_2$ $(1\;{\mu}M)$ decreased both the frequency and amplitude of the pacemaker currents and increased the resting currents in the outward direction. $PGE_2$ had only inhibitory effects on pacemaker currents and this inhibitory effect was dose-dependent. For characterization of specific membrane EP receptor subtypes, involved in the effects of $PGE_2$ on pacemaker currents in ICCs, EP receptor agonists were used: Butaprost $(1\;{\mu}M)$, $EP_2$ receptor agonist, reduced the spontaneous inward current frequency and amplitude in cultured ICCs (n=5). However sulprostone $(1\;{\mu}M)$, a mixed $EP_1$ and $EP_3$ agonist, had no effects on the frequency, amplitude and resting currents of pacemaker currents (n=5). SQ-22536 (an inhibitor of adenylate cyclase; $100\;{\mu}M$) and ODQ (an inhibitor of guanylate cyclase; $100\;{\mu}M$) had no effects on $PGE_2$ actions of pacemaker currents. These observations indicate that $PGE_2$ alter directly the pacemaker currents in ICCs, and that the $PGE_2$ receptor subtypes involved are the $EP_2$ receptor, independent of cyclic AMP- and GMP-dependent pathway.

• Archives of Pharmacal Research
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• v.21 no.4
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• pp.423-428
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• 1998

The ligand binding signals to a wide variety of seven transmembrane cell surface receptors are transduced into intracellular signals through heterotrimeric G-proteins. Recently, there have been reports which show diverse coupling patterns of ligand-activated receptors to the members of Gq family $\alpha$ subunits. In order to shed some light on these complex signal processing networks, interactions between G$\alpha$q family of G protein and neurokinin-2 receptor as well as muscarinic M$_{1}$ receptor, which are considered to be new thearpeutic targets in asthma, were studied. Using washed membranes from Cos-7 cells co-transfected with different G.alpha.q and receptor cDNAs, the receptors were stimulated with various concentrations of carbachol and neurokinin A and the agonist-dependent release of [$^3H$]inositol phosphates through phospholipase C beta-1 activation was measured. Differential coupling of Gaq family of G-protein to muscarinic M$_{1}$ receptor and neurokinin-2 receptor was observed. The neurokinin-2 receptor shows a ligand-mediated response in membranes co-transfected with G$\alpha$q, G$\alpha$11 and G$\alpha$14 but not G$\alpha$16 and the ability of the muscarinic $M_1$ receptor to activate phospholipase C through G$\alpha$/11 but not G$\alpha$14 and G$\alpha$16 was demonstrated. Clearly G$\alpha$/11 can couple $\M_1$ and neurokinin-2 receptor to activate phospholipase C. But, there are differences in the relative coupling of the G$\alpha$14 and G$\alpha$16 subunits to these receptors.

• Environmental Mutagens and Carcinogens
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• v.21 no.2
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• pp.95-98
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• 2001

$\beta$$_2$-Adrenergic receptors($\beta$$_2$-AR) contribute to cardiovascular regulation by influencing several functions and a several studies suggest that a decreased function of the $\beta$$_2$-AR may be involved in essential hypertension. We investigated the Arg16Gly mutation of $\beta$$_2$-AR gene, which show enhanced agonist-promoted downregulation of the receptor and yielded different results in terms of association with essential hypertension. We studied the relationship between genetic variation in the $\beta$$_2$-adrenergic receptor gene and hypertension in a Korean population using Nde I restriction fragment length polymorphism (RFLP) analysis. There were significant differences in allele and genotype frequencies between essential hypertensive and normotensive group (Odds ratio(CI) = 1.71 (1.09-2.70)). Therefore, our result suggests that the Nde I RELP of the $\beta$$_2$-adrenergic receptor gene may be useful as a genetic marker in hypertension diagnostics in Korean population.

• YAKHAK HOEJI
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• v.41 no.1
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• pp.139-146
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• 1997

In the present study, capsaicin-induced desensitization of peripheral sensory nerves were investigated by using guinea pig bronchi, in which these nerves are stimulated with cap saicin to produce a contractile response via the release of sensory neuropeptides such as substance P and neurokinin A. The contractile response to capsaicin was inhibited by the combination of CP96345 and SR 48968 suggesting that the excitatory effect of capsaicin is mediated via both the tachykinin NK-1 and NK-2 receptor. Capsaicin produced in vitro-desensitization in dose-dependent manner, but after this in vitro-desensitization the response to NK-1 and NK-2 receptor agonist did not change. Systemic administration (s.c.) of capsaicin also desensitized significantly bronchial tissues but could not produce any change in the contractile response to the selective agonists of NK-1 and NK-2 receptor. Therefore, the present results suggest that functional desensitization to capsaicin-induced contractile response in guinea pig bronchi does not involve NK-1 and NK-2 receptor, while excitatory effect of capsaicin is mediated via both NK-1 and NK-2 receptor. In conclusion, it is suggested that capsaicin- induced excitation and desensitization involves somewhat different pathways.

• Biomolecules & Therapeutics
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• v.26 no.6
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• pp.599-607
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• 2018

Fasiglifam (TAK-875) a G-protein coupled receptor 40 (GPR40) agonist, significantly improves hyperglycemia without hypoglycemia and weight gain, the major side effects of conventional anti-diabetics. Unfortunately, during multi-center Phase 3 clinical trials, unexpected liver toxicity resulted in premature termination of its development. Here, we investigated whether TAK-875 directly inflicts toxicity on hepatocytes and explored its underlying mechanism of toxicity. TAK-875 decreased viability of 2D and 3D cultures of HepG2, a human hepatocarcinoma cell line, in concentration-(>$50{\mu}M$) and time-dependent manners, both of which corresponded with ROS generation. An antioxidant, N-acetylcysteine, attenuated TAK-875-mediated hepatotoxicity, which confirmed the role of ROS generation. Of note, knockdown of GPR40 using siRNA abolished the hepatotoxicity of TAK-875 and attenuated ROS generation. In contrast, TAK-875 induced no cytotoxicity in fibroblasts up to $500{\mu}M$. Supporting the hepatotoxic potential of TAK-875, exposure to TAK-875 resulted in increased mortality of zebrafish larvae at$25{\mu}M$. Histopathological examination of zebrafish exposed to TAK-875 revealed severe hepatotoxicity as manifested by degenerated hypertrophic hepatocytes with cytoplasmic vacuolation and acentric nuclei, confirming that TAK-875 may induce direct hepatotoxicity and that ROS generation may be involved in a GPR40-dependent manner.

• The Korean Journal of Physiology
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• v.24 no.1
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• pp.145-159
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• 1990

Recently, it has been suggested that the endogenous adenosine may be the mediator for the intercellular communication in the regulation of tubuloglomerular feedback control and renin release. Even though two subclasses of adenosine receptors, A1 and A2, have been described, their functional roles are controversial. The present study was undertaken to clarify the role of adenosine receptors in hypertensive rabbit caused by clamping of renal artery. Experiments were done in two-kidney one clip Goldblatt hypertensive rabbits (2K1GHR) and sham-operated normotensive rabbits. Adenosine, N6-cyclohexyladenosine (CHA) and 5'-N-ethylcarboxamidoadenosine (NECA) were infused into a renal artery. The decreases in urine volume, renal blood flow, glomerular filtration rate and excreted amounts of electrolytes caused by adenosine and CHA were significantly attenuated in 2K1CHR. However, changes in renal function caused by A2 adenosine receptor agonist, NECA, tend to be accentuated in 2K1CHR. These results suggest that the attenuation of renal effect caused by adenosine and A1 adenosine receptor agonist may be due to the modification of adenosine receptor in the kidney in Goldblatt hypertensive rabbits.

• Toxicological Research
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• v.22 no.4
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• pp.365-373
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• 2006

The present study was designed to characterize the effects of estrogen receptor agonist (4,4',4'-(4-Propyl-[1H]-pyrazole-1,3,5-triyl) trisphenol, PPT) on liver and kidney in male mouse using a light microscopic analysis. PPT was subcutaneously given to adult male mice at a weekly dosage of 178.6mg/kg in a volume 0.08 ml of vehicle for 3, 5 and 8 weeks. There were differences in body and organ weights between control and the treated groups. Body and kidney weights were decreased in treated group whereas, liver weight was increased. In microscopic observations, sinusoidal diameter in liver of treated group was increased 156%, 216% and 255% on week 3, 5 and 8 respectively. Compared to the control, diameter of proximal convoluted tubules in kidney was increased 37% and 43% or week 5 and 8 in treated group. Whereas, height of epithelial cells in the proximal tubules was reduced at all time points. These results suggest that microstructure of liver and kidney was changed by treatment of estrogen receptor agonist PPT in the male mice.

• Korean Journal of Veterinary Research
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• v.39 no.6
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• pp.1073-1080
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• 1999

Previous studies suggested that the inhibition of thyroxine ($T_4$) release by ${\alpha}_1$-adrenoceptor and muscarinic receptor stimulation results in activated protein kinase C (PKC) from mouse and guinea pig thyroids. In the present study, the effect of carbachol, methoxamine, phorbol myristate acetate (PMA), and R59022 on the release of $T_4$ from the mouse, rat, and guinea pig thyroids was compared to clarify the role of PKC in the regulation of the release of $T_4$. The thyroids were incubated in the medium containing the test agents, samples of the medium were assayed for $T_4$ by EIA kits. Forskolin, an adenylate cyclase activator, chlorophenylthio-cAMP sodium, a membrane permeable analog of cAMP, and isobutyl-methylxanthine, a phosphodiesterase inhibitor, like TSH (thyroid stimulating hormone), enhaced the release of $T_4$ from the mouse, rat, and guinea pig thyroids. Methoxamine, an ${\alpha}_1$-adrenoceptor agonist, inhibited the TSH-stimulated release of $T_4$ in mouse, but not rat and guinea pig thyroids. In contrast, carbachol, a muscarinic receptor agonist, inhibited the release of $T_4$ in guinea pig, but not mouse and rat thyroids. These inhibition were reversed by prazosin, an ${\alpha}_1$-adrenoceptor antagonist or atropine, a muscarinic antagonist or $M_1$- and $M_3$-muscarinic antagonists, in mouse or guinea pig thyroids. In addition, staurosporine, a PKC inhibitor, reversed methoxamine or carbachol inhibition of TSH stimulation. Furthermore, PMA, a PKC activator, and R59022, a diacylglycerol (DAG) kinase inhibitor, inhibited the TSH-stimulated release of $T_4$ in mouse, rat, and guinea pig thyroids. These inhibition were blocked by staurosporine. These findings suggest that the activation of receptor or DAG inhibits TSH-stimulated $T_4$ release through a PKC-dependent mechanism in thyroid gland.

• BMB Reports
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• v.55 no.11
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• pp.547-552
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• 2022

Sorafenib, originally identified as an inhibitor of multiple oncogenic kinases, induces ferroptosis in hepatocellular carcinoma (HCC) cells. Several pathways that mitigate sorafenib-induced ferroptosis confer drug resistance; thus strategies that enhance ferroptosis increase sorafenib efficacy. Orphan nuclear receptor estrogen-related receptor γ (ERRγ) is upregulated in human HCC tissues and plays a role in cancer cell proliferation. The aim of this study was to determine whether inhibition of ERRγ with DN200434, an orally available inverse agonist, can overcome resistance to sorafenib through induction of ferroptosis. Sorafenib-resistant HCC cells were less sensitive to sorafenibinduced ferroptosis and showed significantly higher ERRγ levels than sorafenib-sensitive HCC cells. DN200434 induced lipid peroxidation and ferroptosis in sorafenib-resistant HCC cells. Mechanistically, DN200434 increased mitochondrial ROS generation by reducing glutathione/glutathione disulfide levels, which subsequently reduced mTOR activity and GPX4 levels. DN200434 induced amplification of the antitumor effects of sorafenib was confirmed in a tumor xenograft model. The present results indicate that DN200434 may be a novel therapeutic strategy to re-sensitize HCC cells to sorafenib.