• The Korean Journal of Physiology and Pharmacology
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• v.9 no.4
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• pp.209-213
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• 2005

Interstitial cells of Cajal (ICCs) are the pacemaker cells that generate slow waves in the gastrointestinal (GI) tract. In the present study, we investigated the effect of mitochondrial ATP-sensitive potassium (mitoKATP) channel on pacemaking activity in cultured ICCs from murine small intestine by using whole-cell patch clamp techniques. Under current clamp mode, at 10μM glibenclamide, there was no change in pacemaking activity of ICCs. At $30{\mu}M$ glibenclamide, an inhibitor of the ATP sensitive $K^+$ channels, we could find two examples. If pacemaking activity of ICCs was irregulating, pacemaking activity of ICCs was changed into regulating and if in normal conditions, membrane potential amplitude was increased. At $50{\mu}M$ glibenclamide, the resting membrane potential was depolarized. At 3mM 5-HDA, an inhibitor of the mitoKATP channels, inhibited the pacemaking activity of ICCs. Both the amplitude and the frequency were decreased. At 5 mM 5-HDA, both the amplitude and the frequency were completely abolished. Diazoxide, an opener of the mitoKATP channels, was applied to examine its effect on pacemaking activity of ICCs. At $50{\mu}M$ concentration, the pacemaking activity of ICCs was inhibited. Both the amplitude and the frequency were decreased. At 1 mM concentration, both the amplitude and the frequency were completely abolished and the resting membrane potential was shaked.These results indicate that mitoKATP channel has an important role in pacemaking activity of ICCs.

• The Korean Journal of Physiology and Pharmacology
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• v.8 no.2
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• pp.95-100
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• 2004

Ischemic preconditioning (IPC) has been accepted as a heart protection phenomenon against ischemia and reperfusion (I/R) injury. The activation of ATP-sensitive potassium $(K_{ATP})$ channels and the release of myocardial nitric oxide (NO) induced by IPC were demonstrated as the triggers or mediators of IPC. A common action mechanism of NO is a direct or indirect increase in tissue cGMP content. Furthermore, cGMP has also been shown to contribute cardiac protective effect to reduce heart I/R-induced infarction. The present investigation tested the hypothesis that $K_{ATP}$ channels attenuate DNA strand breaks and oxidative damage in an in vitro model of I/R utilizing rat ventricular myocytes. We estimated DNA strand breaks and oxidative damage by mean of single cell gel electrophoresis with endonuclease III cutting sites (comet assay). In the I/R model, the level of DNA damage increased massively. Preconditioning with a single 5-min anoxia, diazoxide $(100\;{\mu}M)$, SNAP $(300\;{\mu}M)$ and 8-(4-Chlorophenylthio)-guanosine-3',5'-cyclic monophosphate (8-pCPT-cGMP) $(100\;{\mu}M)$ followed by 15 min reoxygenation reduced DNA damage level against subsequent 30 min anoxia and 60 min reoxygenation. These protective effects were blocked by the concomitant presence of glibenclamide $(50\;{\mu}M)$, 5-hydroxydecanoate (5-HD) $(100\;{\mu}M)$ and 8-(4-Chlorophenylthio)-guanosine-3',5'-cyclic monophosphate, Rp-isomer (Rp-8-pCPT-cGMP) $(100\;{\mu}M)$. These results suggest that NO-cGMP-protein kinase G (PKG) pathway contributes to cardioprotective effect of $K_{ATP}$ channels in rat ventricular myocytes.

• Nutrition Research and Practice
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• v.12 no.3
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• pp.183-190
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• 2018

BACKGROUND/OBJECTIVE: This study was designed to investigate how a Portulaca oleracea L. extract (POE) stimulates insulin secretion in INS-1 pancreatic ${\beta}-cells$. MATERIALS/METHOD: INS-1 pancreatic ${\beta}-cells$ were incubated in the presence of various glucose concentrations: 1.1 or 5.6, 16.7 mM glucose. The cells were treated with insulin secretagogues or insulin secretion inhibitor for insulin secretion assay using an insulin ELISA kit. In order to quantify intracellular influx of $Ca^{2+}$ caused by POE treatment, the effect of POE on intracellular $Ca^{2+}$ in INS-1 pancreatic ${\beta}-cells$ was examined using Fluo-2 AM dye. RESULTS: POE at 10 to $200{\mu}g/mL$ significantly increased insulin secretion dose-dependently as compared to the control. Experiments at three glucose concentrations (1.1, 5.6, and 16.7 mM) confirmed that POE significantly stimulated insulin secretion on its own as well as in a glucose-dependent manner. POE also exerted synergistic effects on insulin secretion with secretagogues, such as L-alanine, 3-isobutyl-1-methylxanthine, and especially tolbutamide, and at a depolarizing concentration of KCl. The insulin secretion caused by POE was significantly attenuated by treatment with diazoxide, an opener of the $K{^+}_{ATP}$ channel (blocking insulin secretion) and by verapamil (a $Ca^{2+}$ channel blocker). The insulinotropic effect of POE was not observed under $Ca^{2+}$-free conditions in INS-1 pancreatic ${\beta}-cells$. When the cells were preincubated with a $Ca^{2+}$ fluorescent dye, Fluo-2 (acetoxymethyl ester), the cells treated with POE showed changes in fluorescence in red, green, and blue tones, indicating a significant increase in intracellular $Ca^{2+}$, which closely correlated with increases in the levels of insulin secretion. CONCLUSIONS: These findings indicate that POE stimulates insulin secretion via a $K{^+}_{ATP}$ channel-dependent pathway in INS-1 pancreatic ${\beta}-cells$.

• KSBB Journal
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• v.21 no.6 s.101
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• pp.466-473
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• 2006

Impaired insulin secretion from pancreatic beta-cells in response to glucose is an important feature in the pathology of non-insulin-dependent diabetes mellitus (NIDDM). In the course of screening for useful insulin secretagogues, we have isolated and identified YHB-2017 (Genistein) as a insulin secretion potentiator from fermentation broths of our in-house microbial library. The insulinotropic activity of YHB-2017 in isolated rat pancreatic islets was exerted only at high concentration of glucose (8.3-16 mM) but not at low concentration of glucose (3.3-5.5 mM). Also, in perifusion study with isolated rat pancreatic islets, YHB-2017 stimulated insulin secretion in a time-dependent manner when YHB-2017 was added to KRB buffer containing 16 mM glucose. In the presence of $200\;{\mu}M$ diazoxide and 35 mM KCI, which stimulates maximum $Ca^{2+}$ influx independently of KATP channel, YHB-2017 enhanced KATP channel-independent insulin secretion at high concentration glucose (16 mM). To elucidate the mechanisms of the glucose-dependent potentiation effect of YHB-2017, pharmacologic inhibitors for protein kinase A, protein kinase C and calcium/calmodulin kinase II were pre-treated and then the potentiation effect of YHB-2017 on insulin secretion was investigated. Pre-treatment of H89 as a PKA inhibitor had a significant inhibitory effect on YHB-2017-induced potentiation effect. Furthermore, western immunoblotting analyses revealed that YHB-2017 increased phosphorylation of PKA substrates and cAMP response element-binding protein (CREB) under high concentration of glucose. These results demonstrated that the insulinotropic effect of YHB-2017 is mediated through PKA signal pathway and activated amplifying $K_{ATP}$ channel-independent insulin secretion pathway.

• Proceedings of the Ginseng society Conference
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• 2007.05a
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• pp.23-24
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• 2007

Purpose: 인삼이 항당뇨 활성을 가진다는 연구가 많은 연구자들에 의해 진행되었고, 이는 인삼의 구성 성분 중 ginsenoside에 기인한다는 보고가 있다. 본 연구는 ginsenoside의 항당뇨 작용기전을 in vitro에서 알아보고자 3T3-L1 지방세포에서 glucose uptake와 췌장 베타세포인 HIT-T15 세포에서 insulin 분비 효과를 확인하였다. 이를 위하여 인삼을 식초로 처리한 긴삼의 70% MeOH 분획으로부터 protopanaxadiol 계인 ginsenoside $Rb_2$, $Rg_3$ 그리고 protopanaxtriol 계인 $Rg_2$를 분리하여 본 실험에 사용하였다. Method: Ginsenoside $Rb_2$, $Rg_2$, $Rg_3$가 지방 세포에서 glucose uptake에 미치는 효과를 확인하기 위하여 3T3-L1 세포를 DMEM (Dulbecco's Modified Eagle's Medium) 배지에서 분화 유도시켰으며 3T3-L1 preadipocyte가 80% 정도 자라면 분화 유도 배지 (5% fetal bovine serum (FBS), 0.5 mM isobutylmethylxanthine (IBMX), 1 mM dexamethasone 그리고 $10{\mu}g/ml$ insulin가 포함된 DMEM)로 4일, $10{\mu}g/ml$ insulin가 포함된 DMEM으로 2일, FBS만 포함된 DMEM으로 2일 배양하여 총 8일 동안 분화를 유도하였다. 분화 유도된 3T3-L1 adipocytes 에 각각 $Rb_2$, $Rg_2$, $Rg_3$를 $20{\mu}M$로 처리하여 16시간 배양하여 low glucose DMEM에서 3시간 배양한 후에 $37^{\circ}C$에서 insulin 10 ng/ml 과 각각 $Rb_2$, $Rg_2$, $Rg_3$가 포함된 Krebs Ringer Hepes buffer(KRP buffer)에서 20분간 배양하였다. 2-deoxy-D-[$^3H$]-glucose를 넣고 10분 후에 차가운 PBS로 반응을 종결시켜 lysis buffer로 cell을 모은 후 scintillation counter를 이용하여 glucose를 측정하였다. Insulin 분비 효과는 HIT-T15 세포와 일차 배양한 흰쥐 소도세포(islets)를 사용하여 확인하였다. HIT-T15 세포는 24 well plate에 well 당 $2{\times}10^5$ 개씩 분주하여 24시간 동안 배양한 후 시료를 처리하였으며 소도 세포는 Sprague-Dawley rat의 췌장에 collagenase가 포함된 Hanks' Balanced Salt Solution(HBSS)을 주입하여 분리하고 islets을 얻었다. 분리한 소도세포를 $1{\sim}2$일 동안 배양하여 $Rb_2$, $Rg_2$, $Rg_3$가 각각 $20{\mu}M$의 농도로 첨가된 insulin 측정용 buffer인 Krebs-Ringer buffer (KRB+0.3% BSA, KRBB)에 $37^{\circ}C$에서 1시간 incubation 시킨 후 배양액으로 분비된 인슐린의 양을 측정하였다. 한편 ginsenoside의 인슐린 분비 촉진 기전을 알아보기 위한 실험에서는 ATP-sensitive $K^+$ channel opener인 diazoxide (0.5 mM)가 ginsenoside에 의해 촉진된 인슐린 분비를 억제하는지 살펴보았다. Result: glucose uptake assay 에서는 $Rg_2$가 가장 크게 glucose uptake를 증가시켰고 $Rb_2$, $Rg_3$는 그 활성이 크지 않았다. 한편 Insulin 분비 효과는 diol계인 $Rg_3$에서 용량 의존적으로 인슐린의 분비를 촉진시켰으며 $20{\mu}M$ 농도에서 대조군과 비교해 1.5배 이상의 분비 촉진 효과를 보였고 triol계인 $Rg_2$ 에서는 이러한 효과가 나타나지 않았다. $Rg_3$의 인슐린 분비 촉진 기전을 0.5 mM 의 diazoxide를 이용하여 확인한 결과 $Rg_3$에 의해 촉진된 인슐린 분비를 감소시켰다. 이로 미루어보아 $Rg_3$의 인슐린 분비 촉진 기전은 ATP-sensitive $K^+$ 채널의 봉쇄에 의한 것임을 확인할 수 있었다.

• Journal of Ginseng Research
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• v.31 no.2
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• pp.79-85
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• 2007

Compound K (CK) is a final metabolite of panaxadiol ginsenosides. Although panax ginseng is known to have anti-diabetic activity, the active ingredient is not yet fully identified. Therefore, it would be interesting to know whether and how CK has an anti-diabetic activity. First, insulin secretion-stimulating activity of CK was examined using RIN-m5F cell line and primary cultured islets. CK enhanced the insulin secretion in a concentration dependent manner. This effect, however, was almost completely abolished in the presence of diazoxide, $K^+$ channel opener, indicating that the insulin secretion-stimulating activity of CK is presumably due to blockade of ATP sensitive $K^+$ channel. In addition, effects of CK on gene expressions of hepatic enzymes (phosphoenolpyruvate carboxykinase[PEPCK], glucose-6-phos-phatase[G6Pase]) and on adipocyte differentiation in H4IIE and 3T3-Ll cells, respectively, were examined. CK suppressed the induction of PEPCK and G6Pase mRNA expressions under the dexamethasone/cAMP stimulation condition. CK also reduced the $PPAR-{\gamma}$ mRNA expression and triglyceride accumulation in a dose dependent manner as compared to the control. The present study suggests that CK deserves to examine whether it shows an anti-diabetic activity in animal and human studies.

• The Korean Journal of Pharmacology
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• v.18 no.2
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• pp.15-25
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• 1982

It was undertake to investigate the factors involved in the micro thrombus formation in the plasma from the patients with cerebrovascular disease(CVD) and the in vitro actions of sodium nitroprusside on the platelet aggregate formation. 1) The microthrombus formation in the plasma from CVD was significantly enhanced, in comparison with that from the healthy volunteers. 2) Both lipid peroxide and cathepsin D in the plasma from CVD were higher than those levels from the healthy volunteers. 3) Whereas the platelets from healthy individuals showed less aggregation activity in response to ADP in the second phase those from CVD revealed the enhanced aggregating response to ADP. 4) When the bovine basilar artery, rabbit aorta and human umbilical artery were pretreated with $K^+-free$ PSS, ouabain, 13-hydroperoxylinoleic acid(13-HPLA) and cadmium they markedly enhanced the platelet aggregability respectively. 5) Platelet aggregation induced by $K^+-free$ PSS-treated bovine basilar artery was decreased by sodium nitroprusside in a dose-dependent manner, but not by either hydralazine. 6) Both dibutyryl cyclic AMP and 8-bromo cyclic GMP had the inhibitory action on the platelet aggregation. However, the latter had more prominent action than former. The antiaggregating effect by sodium nitroprusside was antagonized by pretreatment with methylene blue, but not by hemoglobin. These results provide the evidences for the therapeutic use of sodium nitroprusside in the emergency of cerebrovascular disease and in remains the further study of the clinical therapy with it.