• Biomolecules & Therapeutics
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• v.13 no.1
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• pp.35-40
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• 2005

This study was performed to investigate the regulatory mechanism of cerebral blood flow of adenosine A$_{2B}$ receptor agonist in the rats, and to define whether its mechanism is mediated by adenylate cyclase, guanylate cyclase and potassium channel. In pentobarbital-anesthetized, pancuronium-paralyzed and artificially ventilated male Sprague-Dawley rats, all drugs were applied topically to the cerebral cortex. Blood flow from cerebral cortex was measured using laser-Doppler flowmetry. Topical application of an adenosine A$_{2B}$ receptor agonist, 5'-N-ethylcarboxamidoadenosine (NECA; 4 umol/I) increased cerebral blood flow. This effect of NECA (4 umol/I) was not blocked by pretreatment with adenylate cyclase inhibitor, MDL-12,330 (20 umol/I). But effect of NECA (4 umol/I) was blocked by pretreatment with guanylate cyclase inhibitor, LY-83,583 (10 umol/I) and pretreatment with ATP-sensitive potassium channel inhibitor, glipizide (5 umol/I). These results suggest that adenosine A$_{2B}$ receptor increases cerebral blood flow. It seems that this action of adenosine A$_{2B}$ receptor is mediated via the activation of guanylate cyclase and ATP-sensitive potassium channel in the cerebral cortex of the rats.

• The Korean Journal of Physiology and Pharmacology
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• v.4 no.2
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• pp.105-111
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• 2000

Stimulation of muscarinic receptors by carbachol (CCh) in the circular smooth muscle of the guinea pig gastric antrum causes muscle contraction. In the present study, muscarinic receptor subtype controlling the muscle contraction in response to CCh was studied using putative muscarinic receptor antagonists. Isometric force of the isolated circular muscle strips was measured in an organ bath. CCh contracted the muscle in a dose-dependent way, and each of the three muscarinic receptor antagonists, 4-diphenylacetoxy- N-methylpeperdine methiodide (4-DAMP), methoctramine and pirenzepine shifted the concentration- response curves to the right without significantly reducing the maximum force. The affinities of the muscarinic antagonists $(pA_2\;values)$ obtained from Schild plot analysis were 10.15, 7.05 and 6.84 for 4-DAMP, methoctramine and pirenzepine, respectively. These results suggest that the $M_3-subtype$ mainly mediate the muscle contraction in response to CCh in guinea pig gastric antrum.

• The Korean Journal of Physiology and Pharmacology
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• v.2 no.1
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• pp.41-48
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• 1998

The present study was undertaken to characterize homocysteic acid (HCA)-and cysteic acid (CA)-mediated formation of inositol phosphates (InsP) in primary culture of rat cerebellar granule cells. HCA and CA stimulated InsP formation in a dose-dependent manner, which was prevented by the N-methyl-D-aspartate (NMDA) receptor antagonist D,L-2-amino-5-phosphopentanoic acid (APV). CA-, but not HCA-, mediated InsP formation was in part prevented by the metabotropic glutamate receptor antagonist ?${\alpha}$-methyl-4-carboxyphenylglycine ($({\pm})$-MCPG). Both HCA- and CA-mediated increases in intracellular calcium concentration were completely blocked by APV, but were not altered by $({\pm})$-MCPG. CA-mediated InsP formation was in part prevented by removal of endogenous glutamate. In contrast, the glutamate transport blocker L-aspartic acid-${\beta}$-hydroxamate synergistically increased CA responses. These data indicate that in cerebellar granule cells HCA mediates InsP formation wholly by activating NMDA receptor. In contrast, CA stimulates InsP formation by activating both NMDA receptor and metabotropic glutamate receptor, and in part by releasing endogenous glutamate into extracellular milieu.

• 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.

• YAKHAK HOEJI
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• v.34 no.4
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• pp.224-237
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• 1990

A single uniform population of specific, saturable, high affinity binding site of $[^3H]QNB$ guinuclidinyl benzilate(QNB) was identified in the rat cerebral microsomes. The Kd value(37.2 pM) for $[^3H]QNB$ calculated from the kinetically derived rate constants was in agreement with the Kd value(48.9 pM) determined by analysis of saturation isotherms at various receptor concentrations. Dimenhydrinate(DMH), histamine $H_1-blocker$, increased Kd value for $[^3H]QNB$ QNB without affecting the binding site concentrations and this effect resulted from the ability of DMH to slow $[^3H]QNB-receptor$ association. Pirenzepine inhibition curve of $[^3H]QNB$ binding was shallow(nH = 0.52) indicating the presence of two receptor subtypes with high ($M_1-site$) and low($M_2-site$) affinity for pirenzepine. Analysis of these inhibition curves yielded that 68% of the total receptor populations were of the $M_1-subtype$ and the remaining 32% of the $M_2-subtype$. Ki values for the $M_1-$ and $M_2-subtypes$ were 2.42 nM and 629.3 nM, respectively. Ki values for $H_1-blockers$ that inhibited $[^3H]QNB$ binding varied with a wide range ($0.02-2.5\;{\mu}M$). The Pseudo-Hill coefficients for inhibition of $[^3H]QNB$ binding by most of $H_1-blockers$ examined except for oxomemazine inhibition of $[^3H]QNB$ binding were close to one. The inhibition curve for oxomemazine in competition with $[^3H]QNB$ was shallow(nH = 0.74) indicating the presence of two receptor populations with different affinities for this drug. The proportion of high and low affinity was 33:67. The Ki values for oxomemazine were $0.045{\pm}0.016\;{\mu}M$ for high affinity and $1.145{\pm}0.232\;{\mu}M$ for low affinity sites. These data indicate that muscarinic receptor blocking potency of $H_1-blockers$ varies widely between different drugs and that most of $H_1-blockers$ examined are nonselective antagonist for the muscarinic receptor subtypes, whereas oxomemazine might be capable of distinguishing between subclasses of muscarinic receptor.

• 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.

• Microbiology and Biotechnology Letters
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• v.24 no.1
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• pp.59-66
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• 1996

Virginiae butanolide C(VB-C) is one of the butyrolactone autoregulators, which triggers the productin of virginiamycin in Streptomyces virginiae. To further understand the mechanism of virginiamycin induction, we isolated three mutants from S. virginiae by N-methyl-N'-nitrosoguanidine (NTG) treatment. The characteristics of the three mutants were confirmed as follows: the mutant No. 1 delayed the production of the VB-C, receptor and antibiotics; the mutant No.3 hyperproduced receptor; the mutant No.4 failed to produce the VB-C. The addition of synthetic VB-C couldn't induce the production of antibiotics in the mutant No.1 due to delayed production of receptor, could provoke the production of larger amount of antibiotics than parental wild type strain in the mutant No.3 due to the presence of large amount of receptor, and could induce production of very small amount of antibiotics in the mutant No.4 due to the absence of VB-C. Antimicrobial spectrum and HPLC analysis of the mutant No.1 and No.3 suggested that the VB-C might have a specific ability to induce the production of virginiamycin M and S. These results imply that the VB-C has an ability to trigger the production of virginiamycin under receptor existence in S. virginiae.

• Biomolecules & Therapeutics
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• v.4 no.2
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• pp.196-201
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• 1996

The N-methyl-D-aspartate (NMDA) receptor-ion channel complex is activated by the simultaneous presence of L-glutamate and glycine, allowing the binding of MK-801 to the phencyclidine (PCP) site of the receptor. The $[^3H]$MK-801 binding assay system was established for determination of pharmacological functions of test compounds acting at the glycine site of the receptor. The binding in the presence of 0.1 $\mu$M L-glutamate was increased by an agonist (glycine) in a dose-dependent fashion, while decreased by either partial agonist (R-(+)-HA-966) or antagonist (5,7-dichlorokynurenic acid: 5,7-DCKA). To distinguish partial agonism from antagonism, various concentrations of 7-chlorokynurenic acid (7-CKA) were added in the assay to eliminate the interference of the endogenous glycine present in the membrane preparations. The bindings in the presence of L-glutamate (0.1$\muM$) and 7-CKA (1, 5, or 10$\muM$) were increased by R-(+)-HA-966. Being a weak partial agonist, the extent of potentiation was much less than that by the agonist. These binding profiles were clearly distinguishable from those by the antagonist, 5,7-DCKA, which exhibited no intrinsic activity. The binding assays established in the present study are a useful system to classify ligands acting at the glycine site of the NMDA receptor by their pharmacological functions.

• Archives of Pharmacal Research
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• v.16 no.4
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• pp.276-282
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• 1993

This study has been undertaken to examine the effect of 3-methylcholanthrene (3MC) on rat uterine growth and to understand the mechanism of action of 3MC in rat uterus. After diethylstilbesterol(DES) or tamoxifen(TAM) or 3MC or DES plus TAM or DES plus 3MC was administered into immature female rats, uterine weight over corn oil-treated uteri. 3MC treatment had no effect on uterine weight but, DES stimulated uterine weight was inhibited by 3MC concomitant tratment. While TAM alone treatment showed slight increase in uterine wieght, inhibited uterine growth simulated by DES when it was adiministrated with DES condirect binding assay with $[^3H]$ estradiol and the relative binding affinities of 3MC and TAM were estimated by competetion assy. Estradiol tumed out to have high affinity for rat uterine estrogen receptor (kd = 0.4 nM). The relative binding affinities of TAM and 3MC were 1% and 4.7% that of DES for rat uterine estrogen receptor, respectively. 3MC was shown to have similar affinity for eat uterine estrogen receptor to that of TAM. Effects of DES 3MC and TAM administration in vivo on rat uterine estrogen recptor level were examined. It was confirmed that the estrogen, DES and antiestrogen, TAM decreased estrogen receptor levels from rat ulterus and also 3MC decreased rat uterine estrogen receptor level when rats were treated with DES, TAM and 3MC in vivo. Data indicates that 3MC acts as an antiestrogen mediated through estrogen receptor system.

• The Korean Journal of Physiology and Pharmacology
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• v.14 no.4
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• pp.223-228
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• 2010

The collecting duct endothelin (ET) system, which involves ET-1 and its two receptors, may play a role in the regulation of renal sodium in association with the nitric oxide synthase (NOS) system. We determined whether sodium retention is associated with changes in the endothelin and NOS systems at different stages (i.e., a sodium retaining stage and a compensatory stage) of nephrotic syndromes. On day 7 after puromycin aminonucleoside (PAN) injection, urinary sodium excretion was decreased, ascites had developed, and there was a positive sodium balance. ET-1 mRNA expression was increased in the inner medulla of the kidney, whereas protein expression of ET receptor type B ($ET_BR$) was unchanged. The expression of neuronal NOS (nNOS) was decreased in the inner medulla. On day 14, urinary sodium excretion was unchanged compared with controls. The expression of $ET_BR$ increased, while nNOS expression in the inner medulla was comparable to controls. These findings suggest that decreased nNOS plays a role in the development of sodium retention in the nephrotic syndrome. Recovery of nNOS and increased renal $ET_BR$ synthesis may promote sodium excretion in later stages of the nephrotic syndrome (on day 14).