• Genomics & Informatics
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• 제5권2호
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• pp.77-82
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• 2007

Serotonin (5-HT), the endogenous nonselective 5-HT receptor agonist, activates the inositol-1,4,5-triphosphate/calcium $(InsP3/Ca^{2+})$ signaling pathway and exerts both stimulatory and inhibitory actions on cAMP production and neuromodulin secretion in rat hypothalamic neurons. Specific mRNA transcripts for 5-HT1A, 5-HT2C and 5-HT4 were identified in rat hypothalamic neurons. These experiments were supported by combined techniques such as cAMP and a $Ca^{2+}$ assays in order to elucidate the associated receptors and signaling pathways. The cAMP production and neuromodulin release were profoundly inhibited during the activation of the Gi-coupled 5-HT1A receptor. Treatment with a selective agonist to activate the Gq-coupled 5-HT2C receptor stimulated InsP3 production and caused $Ca^{2+}$ release from the sarcoplasmic reticulum. Selective activation of the Gs-coupled 5-HT4 receptor also stimulated cAMP production, and caused an increase in neuromodulin secretion. These findings demonstrate the ability of 5-HT receptor subtypes expressed in neurons to induce neuromodulin production. This leads to the activation of single or multiple G-proteins which regulate the $InsP3/Ca^{2+}/PLC-{\gamma}$ and adenyl cyclase / cAMP signaling pathways.

• 대한수의학회지
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• 제34권3호
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• pp.447-456
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• 1994

In order to elucidate the characterization of receptors involved in inestinal motility of Israeli carp, spontaneously contracting Israeli carp intestinal preperations were prepared and mounted in the organ chambers for contraction traicings using a polygraph. Various contractile agonists were treated and their dose-response curves were constructed. $EC_{50}$ values$(pD_2)$ of each agonist on specific receptors, $pA_2$ values of competitive antagonists against some agonists, and $K_1$, values of noncompetitive antagonists against some agonists were analyzed for characterization of receptors related with the intestinal contraction. Results obtained through the experiments were summarized as follows: 1. Acetylcholine(ACh) exhibited biphasic dose-response curves: initial ACh-induced dose dependent contractions were observed in pM levels but followed by decreased response in in-between concentration levels. Dose dependent contractions reappeared in ${\mu}M$ level. The peaks in pM and ${\mu}M$ levels appeared in $10^{-13}M$ and $3{\times}10^{-5}M$, respectvely. 2. Carbachol(CaCh) exhibited dose dependent contractions from $10^{-9}M$ to $10^{-5}M$, and its $pD_2$ values were higher than those of ACh($5.60{\pm}0.11$). ACh and CaCh exhibited equiactive contractions. Nicotine had no effects on contractile responses of Israeli carp intestine. 3. ACh-induced responses were inhibited by atropine($K_1:7{\times}10^{-8}M$), a muscarinic antagonist, in a non-competitive manner. But CaCh-induced responses were inhibited by both antimuscarinic atropine($pA_2:9.52{\pm}0.14$) and selective $M_2$ antagonistic 4-DAMP($pA_2:8.16{\pm}0.09$), in competitive manners. Nicotine receptor antagonistic decamethonium and hexamethonium had no effects on ACh-and CaCh-induced contractions. Therefore, the cholinergic receptor related to intestinal motility of Israeli carp was assumed as $M_2$ type. 4. In Israeli carp intestine, 5-HT (serotonin) exhibited dose dependent contractions in concentration range from $10^{-8}M$ to $10^{-5}M$. The maximal responses, however, were corresponded to about 50% of those of ACh or CaCh. 5-HT induced contractions were inhibited by $5-HT_2$ antagonistic ketanserin ($K_1: 7.8{\times}10^{-4}M$) in a non-competitive manner, but not by both of anti $5-HT_1$, spiperone and anti $5-HT_3$, MDL-72222. Hence, $5-HT_2$ receptors are suggested to be existed in Isreli carp intestine.

• The Korean Journal of Physiology and Pharmacology
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• 제20권6호
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• pp.605-611
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• 2016

Ketamine is an anesthetic with hypertensive effects, which make it useful for patients at risk of shock. However, previous ex vivo studies reported vasodilatory actions of ketamine in isolated arteries. In this study, we reexamined the effects of ketamine on arterial tones in the presence and absence of physiological concentrations of 5-hydroxytryptamine (5-HT) and norepinephrine (NE) by measuring the isometric tension of endothelium-denuded rat mesenteric arterial rings. Ketamine little affected the resting tone of control mesenteric arterial rings, but, in the presence of 5-HT (100~200 nM), ketamine ($10{\sim}100{\mu}M$) markedly contracted the arterial rings. Ketamine did not contract arterial rings in the presence of NE (10 nM), indicating that the vasoconstrictive action of ketamine is 5-HT-dependent. The concentration-response curves (CRCs) of 5-HT were clearly shifted to the left in the presence of ketamine ($30{\mu}M$), whereas the CRCs of NE were little affected by ketamine. The left shift of the 5-HT CRCs caused by ketamine was reversed with ketanserin, a competitive 5-$HT_{2A}$ receptor inhibitor, indicating that ketamine facilitated the activation of 5-$HT_{2A}$ receptors. Anpirtoline and BW723C86, selective agonists of 5-$HT_{1B}$ and 5-$HT_{2B}$ receptors, respectively, did not contract arterial rings in the absence or presence of ketamine. These results indicate that ketamine specifically enhances 5-$HT_{2A}$ receptor-mediated vasoconstriction and that it is vasoconstrictive in a clinical setting. The facilitative action of ketamine on 5-$HT_{2A}$ receptors should be considered in ketamine-induced hypertension as well as in the pathogenesis of diseases such as schizophrenia, wherein experimental animal models are frequently generated using ketamine.