• The Korean Journal of Physiology and Pharmacology
• /
• 제18권4호
• /
• pp.341-346
• /
• 2014

Lubiprostone is a chloride ($Cl^-$) channel activator derived from prostaglandin $E_1$ and used for managing constipation. In addition, lubiprostone affects the activity of gastrointestinal smooth muscles. Interstitial cells of Cajal (ICCs) are pacemaker cells that generate slow-wave activity in smooth muscles. We studied the effects of lubiprostone on the pacemaker potentials of colonic ICCs. We used the whole-cell patch-clamp technique to determine the pacemaker activity in cultured colonic ICCs obtained from mice. Lubiprostone hyperpolarized the membrane and inhibited the generation of pacemaker potentials. Prostanoid $EP_1$, $EP_2$, $EP_3$, and $EP_4$ antagonists (SC-19220, PF-04418948, 6-methoxypyridine-2-boronc acid N-phenyldiethanolamine ester, and GW627368, respectively) did not block the response to lubiprostone. L-NG-nitroarginine methyl ester (L-NAME, an inhibitor of nitric oxide synthase) and 1H-[1,2,4]oxadiazolo[4,3,-a]quinoxalin-1-one (ODQ, an inhibitor of guanylate cyclase) did not block the response to lubiprostone. In addition, tetraethylammonium (TEA, a voltage-dependent potassium [$K^+$] channel blocker) and apamin (a calcium [$Ca^{2+}$]-dependent $K^+$ channel blocker) did not block the response to lubiprostone. However, glibenclamide (an ATP-sensitive $K^+$ channel blocker) blocked the response to lubiprostone. Similar to lubiprostone, pinacidil (an opener of ATP-sensitive $K^+$ channel) hyperpolarized the membrane and inhibited the generation of pacemaker potentials, and these effects were inhibited by glibenclamide. These results suggest that lubiprostone can modulate the pacemaker potentials of colonic ICCs via activation of ATP-sensitive $K^+$ channel through a prostanoid EP receptor-independent mechanism.

• Parasites, Hosts and Diseases
• /
• 제41권2호
• /
• pp.129-133
• /
• 2003

A complete cDNA sequence encoding a pore-forming subunit (Kir6.2) of ATP-senstive potassium channel in the adult worm, Clonorchis sinensis, termed CsKir6.2, was isolated from an adult CDNA library. The cDNA contained a single open-reading frame of 333 amino acids, which has a structural motif (a GFG-motif) of the putative pore-forming loop of the Kir6.2. Peculiarly, the Cskir6.2 shows a lack-sequence structure, which deleted 57 amino acids were deleted from its N-terminus. The predicted amino acid sequence revealed a highly conserved sequence as other known other Kir6.2 subunits. The mRNA was weekly expressed in the adult worm.

• The Korean Journal of Physiology
• /
• 제28권1호
• /
• pp.37-50
• /
• 1994

Synthetic potassium channel openers (KCOs) are agents capable of opening K-channels in excitable cells. These agents are known to have their maximal potency in the smooth muscle tissue, especially in the vascular smooth muscle. Much attention has been focused on the type of K-channel that is responsible for mediating the effects of KCOs. As the KCO-induced changes are antagonized by glibenclamide, an $K_{ATP}$ (ATP-sensitive K-channel) blocker in the pancreatic ${\beta}-cell,\;K_{ATP}$ was suggested to be the channel responsible. However, there also are many results in favor of other types of K-channel $$(maxi-K,\;small\;conductance\;K_{Ca,}\; SK_{ATP}) mediating the effects of KCOs. Effects of lemakalim, (-)enantiomer of cromakalim (BRL 34915), on the spontaneous contractions and slow waves, were investigated in the antral circular muscle of the guinea-pig stomach. Membrane currents and the effects on membrane currents and single channel activities were also measured in single smooth muscle cells and excised membrane patches by using the patch clamp method. Lemakalim induced hyperpolarization and inhibited spontaneous contractions in a dose-dependent manner. These effects were blocked by glibenclamide and low concentrations of tetraethyl ammonium (< mM). Glibenclamide blocked the effect of lemakalim on the membrane potential and slow waves. The mechanoinhibitory effect of lemakalim was blocked by pretreatment with glibenclamide. In a whole ceIl patch clamp condition, lemakalim largely increased outward K currents. These outward K currents were blocked by TEA, glibenclamide and a high concentration of intracelIular EGTA (10 mM). Volatage-gated Ca currents were not affected by lemakalim. In inside-out patch clamp experiments, lemakalim increased the opening frequency of the large conductance $Ca^{2+}-activated$ K channels $(BK_{Ca},\;Maxi-K).$ From these results, it is suggested that lemakalim induces hyperpolarization by opening K-channels which are sensitive to internal Ca and such a hyperpolarization leads to the inhibition of the spontaneous contraction.

• The Korean Journal of Physiology and Pharmacology
• /
• 제11권3호
• /
• pp.97-106
• /
• 2007

The present study was attempted to investigate the effect of nicorandil, which is an ATP-sensitive potassium ($K_{ATP}$) channel opener, on secretion of catecholamines (CA) evoked by cholinergic stimulation and membrane depolarization from the isolated perfused rat adrenal glands. The perfusion of nicorandil ($0.3{\sim}3.0mM$) into an adrenal vein for 90 min produced relatively dose-and time-dependent inhibition in CA secretion evoked by ACh (5.32 mM), high $k^+$ (a direct membrane depolarizer, 56 mM), DMPP (a selective neuronal nicotinic receptor agonist, $100{\mu}M$ for 2 min), McN-A-343 (a selective muscarinic $M_1$ receptor agonist, $100{\mu}M$ for 4 min), Bay-K-8644 (an activator of L-type dihydropyridine $Ca^{2+}$ channels, $10{\mu}M$ for 4 min) and cyclopiazonic acid (an activator of cytoplasmic $Ca^{2+}$-ATPase, $10{\mu}M$ for 4 min). In adrenal glands simultaneously preloaded with nicorandil (1.0 mM) and glibenclamide (a nonspecific $K_{ATP}$-channel blocker, 1.0 mM), the CA secretory responses evoked by ACh, high potassium, DMPP, McN-A-343, Bay-K-8644 and cyclopiazonic acid were recovered to the considerable extent of the control release in comparison with that of nicorandil-treatment only. Taken together, the present study demonstrates that nicorandil inhibits the adrenal CA secretion in response to stimulation of cholinergic (both nicotinic and muscarinic) receptors as well as by membrane depolarization from the isolated perfused rat adrenal glands. It seems that this inhibitory effect of nicorandil may be mediated by inhibiting both $Ca^{2+}$ influx and the $Ca^{2+}$ release from intracellular store through activation of $K_{ATP}$ channels in the rat adrenomedullary chromaffin cells. These results suggest that nicorandil-sensitive $K_{ATP}$ channels may play an inhibitory role in the regulation of the rat adrenomedullary CA secretion.

• The Korean Journal of Physiology and Pharmacology
• /
• 제12권1호
• /
• pp.7-12
• /
• 2008

OLETF (Otsuka Long-Evans Tokushima Fatty) rats are characterized by obesity-related insulin resistance, which is a phenotype of type 2 diabetes. Sulfonylurea drugs or benzoic acid derivatives as inhibitors of the ATP-sensitive potassium $(K_{ATP})$ channel are commercially available to treat diabetes. The present study compared sulfonylurea drugs (glimepiride and gliclazide) with one of benzoic acid derivatives (repaglinide) in regard to their long-term effect on ameliorating insulin sensitivity in OLETF rats. Each drug was dissolved and fed with drinking water from 29 weeks of age. On high glucose loading at 45 weeks of age, response of blood glucose recovery was the greatest in the group treated with glimepiride. On immunohistochemistry analysis for the Kir6.2 subunit of $K_{ATP}$ channels, insulin receptor ${\beta}$-subunits, and glucose transporters (GLUT) type 2 and 4 in liver, fat and skeletal muscle tissues, the sulfonylurea drugs (glimepiride and gliclazide) were more effective than repaglinide in recovery from their decreased expressions in OLETF rats. From these results, it seems to be plausible that $K_{ATP}$-channel inhibitors containing sulfonylurea moiety may be much more effective in reducing insulin resistance than those with benzoic acid moiety. In contrast to gliclazide, non-tissue selectivity of glimepiride on $K_{ATP}$ channel inhibition may further strengthen an amelioration of insulin sensitivity unless considering other side effects.

• 한국응용약물학회:학술대회논문집
• /
• 한국응용약물학회 1998년도 Proceedings of UNESCO-internetwork Cooperative Regional Seminar and Workshop on Bioassay Guided Isolation of Bioactive Substances from Natural Products and Microbial Products
• /
• pp.148-149
• /
• 1998

It has been known that potassium channel openers are a new class of molecules that have attracted general interest because of their potent antihypertensive activity in vivo and vasorelaxant activity in vitro (Hamilton and Weston, 1989). In the present study, it was attempted to examine the effect of the potassium channel opener on catecholamine (CA) secretion evoked by cholinergic stimulation, membrane depolarization and calcium mobilization from the isolated perfused rat adrenal gland. The perfusion of pinacidil (30-300 uM) into an adrenal vein for 20 min produced relatively dose-dependent inhibition in CA secretion evoked by ACh (5.32 mM), high $K^{+}$ (56 mM), DMPP (100 uM for 2 min), McN-A-343 (100 uM for 2 min), cyclopiazonic acid (10 uM for 4 min) and Bay-K-8644 (10 uM for 4 min). Also, under the presence of minoxidil (100 uM), which is also known to be a potassium channel activator, CA secretory responses evoked by ACh, high potassium, DMPP, McN-A-343, Bay-K-8644 and cyclopiazonic acid were also significantly depressed. However, in adrenal glands preloaded with pinacidil (100 uM) under the presence of glibenclamide (1 uM), an antidiabetic sulfonylurea that has been shown to be a specific blocker of ATP-regulated potassium channels (for 20 min), CA secretory responses evoked by ACh, high potassium, DMPP, McN-A-343, Bay-K-8644 and cyclopiazonic acid were considerably recovered to a considerable extent of the normal release as compared to that of pinacidil only. These results, taken together, suggest that pinacidil cause the marked inhibition of CA secretion evoked by stimulation of cholinergic (both nicotinic and muscarinic) receptors as well as by membrane depolarization, indicating strongly that this effect may be mediated by inhibiting influx of extracellular calcium and release in intracellular calcium in the rat adrenomedullary chromaffin cells. Furthermore, these findings suggest strongly that these potassium channel openers-sensitive membrane potassium channels also play an important role in regulating CA secretion.

• The Korean Journal of Physiology and Pharmacology
• /
• 제8권4호
• /
• pp.201-206
• /
• 2004

Mitochondrial ATP-sensitive potassium $(mitoK_{ATP})$ channels play a role in early and late ischemic preconditioning. Nevertheless, the subunit composition of $mitoK_{ATP}$ channels remains unclear. In this study, we investigated the subunit composition of $mitoK_{ATP}$ channels in mitochondria isolated from rat cardiac myocytes. Mitochondria were visualized using the red fluorescence probe, Mitrotracker Red, while $mitoK_{ATP}$ channels were visualized using the green fluorescence probe, glibenclamide-BODIPY. The immunofluorescence confocal microscopy revealed the presence of Kir6.1, Kir6.2 and SUR2 present in the cardiac mitochondria. Western blot analysis was carried to further investigate the nature of $mitoK_{ATP}$ channels. For SUR proteins, a 140-kDa immunoreactive band that corresponded to SUR2, but no SUR1 was detected. For Kir6.2, three bands $({\sim}44,\;{\sim}46,\;and\;{\sim}30\;kDa)$ were detected, and a specific ${\sim}46-kDa$ immunoreactive band corresponding to Kir6.1 was also observed. These observations suggest that the subunits of $mitoK_{ATP}$ channels in rat myocytes include Kir6.1, Kir6.2, and a SUR2-related sulfonylurea-binding protein.

• The Korean Journal of Physiology and Pharmacology
• /
• 제8권2호
• /
• pp.95-100
• /
• 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.

• The Korean Journal of Physiology
• /
• 제29권2호
• /
• pp.225-232
• /
• 1995

The present study was conducted to evaluate the effect of phorbol 12,13-dibutyrate (PDBu) on the contraction of rabbit jugular vein in vitro. PDBu concentrations of greater than 10 nM induced a periodic contraction which was composed of rapid contraction, plateau and slow relaxation. The frequency of periodic contraction increased as PDBu concentration increased. The PDBu-induced contraction was inhibited by staurosporine (100 nM), it was not changed by tetrodotoxin $(1\;{\mu}M).$ In $Ca^{2+}$-free medium, PDBu induced a sustaining contraction, but not periodic contraction. Addition of $Ca^{2+}$ to medium evoked periodic contraction which was inhibited by nifedipine, PDBu concentrations of greater than $0.1\;{\mu}M$ increased ^{45}Ca^{2+}$ uptake without changing $^{45}Ca^{2+}$ efflux. Charybdotoxin and apamin, $Ca^{2+}$-activated K^{+}$ channel blockers, did not affect the PDBu-induced periodic contraction, whereas tetraethylammonium (TEA) abolished the periodicity. Pinacidil $(10\;{\mu}M).$, a potassium channel activator, blocked PDBu induced periodic contraction, which was recovered by glybenclamide $(10\;{\mu}M).$. In high potassium solution, PDBu did not produce the periodic contraction. These results suggest that the PDBu-induced periodicity of contraction is modulated by voltage dependent $Ca^{2+}$ channel and ATP-sensitive $K^{+}$ channel.

• Bulletin of the Korean Chemical Society
• /
• 제25권2호
• /
• pp.207-212
• /
• 2004

In this study, we attempted to prepare compounds with heterocyclic replacements for metabolically unstable esters of benzopyranyl indole-2-carboxylic esters, which showed good in vitro and in vivo cardioprotective efficacies possibly through the opening of mitochondrial ATP-sensitive potassium channel ($K_{ATP}$). Initially, we tried to construct indolin-2-yl-heterocycles using unprotected indoline-2-carboxylic acid, but the cyclization was proceeded with oxidation of the indoline ring to the indole, which didn't react with benzopyranyl epoxide. Thus we introduced N-Boc group to deplete the electron density of the indoline ring. We successfully prepared various indolin-2-yl-heterocycles by the cyclization of the building blocks including carboxamide, ${\beta}$-hydroxy amide, hydrazide, nitrile starting from N-Boc-indoline-2-carboxylic acid.