• The Korean Journal of Pharmacology
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• v.24 no.1
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• pp.17-29
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• 1988

The author examined the effects of lidocaine on the veratrine-or potassium-induced release of neurotransmitters to determine the possible role of amino acid neurotransmitters in lidocaine-induced convulsion. The examined transmitters were gamma-aminobutyric acid (GABA), aspartic acid, glutamic acid and norepinephrine which are released from the synaptosomes. Furthermore, the effects of lidocaine on the binding to receptors and synaptosomal uptake of the two transmitters, GABA and glutamic acid, were determined in crude synaptic membranes and synaptosomes. In addition, the effects of propranolol, norepinephrine and serotonin on the release of amino acid neurotransmitters were also examined. The veratrine-induced release of GABA was most severely inhibited by lidocaine and propranolol, while norepinephrine and serotonin reduced the release of aspartic acid and glutamic acid more than the GABA release. Generally the potassium-induced release was much more resistant to the lidocaine action than the veratrine-induced release. Among the neurotransmitters examined, the aspartic acid release was most prone to the lidocaine action, while the GABA release was most resistant. Concentrations of lidocaine below 1 mM did not significantly change the GABA and glutamic acid receptor binding and uptake. These results indicate that the blocking of sodium channels by lidocaine can result in the selective depression of the GABA release. This may result in unlimited excitation of the central nervous system.

• The Korean Journal of Pharmacology
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• v.29 no.2
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• pp.245-252
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• 1993

Amiloride is a potassium sparing duretic which specifically inhibits $Na{^+}$ channels. In the present study, we investigated the possible interaction of amiloride with $A_1$ adenosine receptors-adenylyl cyclase system in crude adipocytic plasma membrane fractions prepared from Sprague-Dawley rats. When the function of $G_i$ protein (inhibitory guanine nucleotide binding protein) was assessed by determining the effects of GTP on isoproterenol-stimulated adenylyl cyclase activity, the inhibitory effect of high concentrations of GTP was not observed in the presence of amiloride. In contrast, the adenosine receptor-mediated inhibition of the enzyme activity, as determined empolying 2-chloroadenosine, was either unchanged or even more enhanced by amiloride depending on the concentrations of 2-chloroadenosine. Thus, it appears that GTP- and receptor-mediated inhibitory function of $G_{i}$ proteins can be separated from one another. Receptor-mediated function of $G_{s}$ protein did not appear to be significantly affected by amiloride, since the inhibition of isoproterenol-stimulated adenylyl cyclase activity by propranolol under the same conditions was not significantly altered by amiloride. The enhancement of 2-chloroadenosine-mediated inhibition of adenylyl cyclase by amiloride was maintained in the presence of 150 mM NaCl. In summary, these results suggest that amiloride interacts both with $A_{l}$ adenosine receptors and with $G_i$ proteins in adipocytic membranes. Its binding to the $A_1$ adenosine receptors appears to facilitate the coupling of the receptors with $G_i$ proteins thereby enhancing the inhibition of isoproterenol-stimulated adenylyl cyclase activity by $A_1$ adenosine agonist, and the direct interaction with $G_i$ proteins appears to remove the GTP-dependent inhibitory effect on adenylyl cyclase activity.

• The Korean Journal of Physiology and Pharmacology
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• v.13 no.1
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• pp.61-70
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• 2009

We have examined the effects of certain mutations of the selectivity filter and of the membrane helix M2 on $Ba^{2+}$ blockage of the inward rectifier potassium channel, Kir 2.1. We expressed mutant and wild type murine Kir 2.1 in Chinese hamster ovary(CHO) cells and used the whole cell patch-clamp technique to record $K^+$ currents in the absence and presence of externally applied $Ba^{2+}$. Wild type Kir2.1 was blocked by externally applied $Ba^{2+}$ in a voltage and concentration dependent manner. Mutants of Y145 in the selectivity filter showed little change in the kinetics of $Ba^{2+}$ blockage. The estimated $K_d(0)$ was 108 ${\mu}M$ for Kir2.1 wild type, 124 ${\mu}M$ for a concatameric WT-Y145V dimer, 109 ${\mu}M$ for a WT-Y145L dimer, and 267 ${\mu}M$ for Y145F. Mutant channels T141A and S165L exhibit a reduced affinity together with a large reduction in the rate of blockage. In S165L, blockage proceeds with a double exponential time course, suggestive of more than one blocking site. The double mutation T141A/S165L dramatically reduced affinity for $Ba^{2+}$, also showing two components with very different time courses. Mutants D172K and D172R(lining the central, aqueous cavity of the channel) showed both a decreased affinity to $Ba^{2+}$ and a decrease in the on transition rate constant(${\kappa}_{on}$). These results imply that residues stabilising the cytoplasmic end of the selectivity filter(T141, S165) and in the central cavity(D172) are major determinants of high affinity $Ba^{2+}$ blockage in Kir 2.1.

• The Korean Journal of Pain
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• v.27 no.3
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• pp.229-238
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• 2014

Background: A toxic dose of bupivacaine produces vasodilation in isolated aortas. The goal of this in vitro study was to investigate the cellular mechanism associated with bupivacaine-induced vasodilation in isolated endothelium-denuded rat aortas precontracted with phenylephrine. Methods: Isolated endothelium-denuded rat aortas were suspended for isometric tension recordings. The effects of nifedipine, verapamil, iberiotoxin, 4-aminopyridine, barium chloride, and glibenclamide on bupivacaine concentration-response curves were assessed in endothelium-denuded aortas precontracted with phenylephrine. The effect of phenylephrine and KCl used for precontraction on bupivacaine-induced concentration-response curves was assessed. The effects of verapamil on phenylephrine concentration-response curves were assessed. The effects of bupivacaine on the intracellular calcium concentration ($[Ca^{2+}]_i$) and tension in aortas precontracted with phenylephrine were measured simultaneously with the acetoxymethyl ester of a fura-2-loaded aortic strip. Results: Pretreatment with potassium channel inhibitors had no effect on bupivacaine-induced relaxation in the endothelium-denuded aortas precontracted with phenylephrine, whereas verapamil or nifedipine attenuated bupivacaine-induced relaxation. The magnitude of the bupivacaine-induced relaxation was enhanced in the 100mM KCl-induced precontracted aortas compared with the phenylephrine-induced precontracted aortas. Verapamil attenuated the phenylephrine-induced contraction. The magnitude of the bupivacaine-induced relaxation was higher than that of the bupivacaine-induced $[Ca^{2+}]_i$ decrease in the aortas precontracted with phenylephrine. Conclusions: Taken together, these results suggest that toxic-dose bupivacaine-induced vasodilation appears to be mediated by decreased calcium sensitization in endothelium-denuded aortas precontracted with phenylephrine. In addition, potassium channel inhibitors had no effect on bupivacaine-induced relaxation. Toxic-dose bupivacaine-induced vasodilation may be partially associated with the inhibitory effect of voltage-operated calcium channels.

• Journal of Ginseng Research
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• v.39 no.4
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• pp.314-321
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• 2015

Background: Ginseng belongs to the genus Panax. Its main active ingredients are the ginsenosides. Interstitial cells of Cajal (ICCs) are the pacemaker cells of the gastrointestinal (GI) tract. To understand the effects of ginsenoside Re (GRe) on GI motility, the authors investigated its effects on the pacemaker activity of ICCs of the murine small intestine. Methods: Interstitial cells of Cajal were dissociated from mouse small intestines by enzymatic digestion. The whole-cell patch clamp configuration was used to record pacemaker potentials in cultured ICCs. Changes in cyclic guanosine monophosphate (cGMP) content induced by GRe were investigated. Results: Ginsenoside Re ($20-40{\mu}M$) decreased the amplitude and frequency of ICC pacemaker activity in a concentration-dependent manner. This action was blocked by guanosine 50-[${\beta}-thio$]diphosphate [a guanosine-5'-triphosphate (GTP)-binding protein inhibitor] and by glibenclamide [an adenosine triphosphate (ATP)-sensitive $K^{+}$ channel blocker]. To study the GRe-induced signaling pathway in ICCs, the effects of 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (a guanylate cyclase inhibitor) and RP-8-CPT-cGMPS (a protein kinase G inhibitor) were examined. Both inhibitors blocked the inhibitory effect of GRe on ICC pacemaker activity. L-NG-nitroarginine methyl ester ($100{\mu}M$), which is a nonselective nitric oxide synthase (NOS) inhibitor, blocked the effects of GRe on ICC pacemaker activity and GRe-stimulated cGMP production in ICCs. Conclusion: In cultured murine ICCs, GRe inhibits the pacemaker activity of ICCs via the ATP-sensitive potassium ($K^{+}$) channel and the cGMP/NO-dependent pathway. Ginsenoside Re may be a basis for developing novel spasmolytic agents to prevent or alleviate GI motility dysfunction.

• Journal of Ginseng Research
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• v.41 no.1
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• pp.103-112
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• 2017

Background: 20(S)-Protopanaxadiol 20-O-D-glucopyranoside, also called compound K (CK), exerts antidiabetic effects that are mediated by insulin secretion through adenosine triphosphate (ATP)-sensitive potassium ($K_{ATP}$) channels in pancreatic ${\beta}$-cells. However, the antidiabetic effects of CK may be limited because of its low bioavailability. Methods: In this study, we aimed to enhance the antidiabetic activity and lower the toxicity of CK by including it with ${\beta}$-cyclodextrin (CD) (CD-CK), and to determine whether the CD-CK compound enhanced pancreatic islet recovery, compared to CK alone, in an alloxan-induced diabetic zebrafish model. Furthermore, we confirmed the toxicity of CD-CK relative to CK alone by morphological changes, mitochondrial damage, and TdT-UTP nick end labeling (TUNEL) assays, and determined the ratio between the toxic and therapeutic dose for both compounds to verify the relative safety of CK and CD-CK. Results: The CD-CK conjugate ($EC_{50}=2.158{\mu}M$) enhanced the recovery of pancreatic islets, compared to CK alone ($EC_{50}=7.221{\mu}M$), as assessed in alloxan-induced diabetic zebrafish larvae. In addition, CD-CK ($LC_{50} =20.68{\mu}M$) was less toxic than CK alone ($LC_{50}=14.24{\mu}M$). The therapeutic index of CK and CD-CK was 1.98 and 9.58, respectively. Conclusion: The CD-CK inclusion complex enhanced the recovery of damaged pancreatic islets in diabetic zebrafish. The CD-CK inclusion complex has potential as an effective antidiabetic efficacy with lower toxicity.

• The Korean Journal of Physiology and Pharmacology
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• v.17 no.6
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• pp.511-516
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• 2013

Bladder cancer is the seventh most common cancer in men that smoke, and the incidence of disease increases with age. The mechanism of occurrence has not yet been established. Potassium channels have been linked with cell proliferation. Some two-pore domain $K^+$ channels (K2P), such as TASK3 and TREK1, have recently been shown to be overexpressed in cancer cells. Here we focused on the relationship between cell growth and the mechanosensitive K2P channel, TREK2, in the human bladder cancer cell line, 253J. We confirmed that TREK2 was expressed in bladder cancer cell lines by Western blot and quantitative real-time PCR. Using the patch-clamp technique, the mechanosensitive TREK2 channel was recorded in the presence of symmetrical 150 mM KCl solutions. In 253J cells, the TREK2 channel was activated by polyunsaturated fatty acids, intracellular acidosis at -60 mV and mechanical stretch at -40 mV or 40 mV. Furthermore, small interfering RNA (siRNA)-mediated TREK2 knockdown resulted in a slight depolarization from $-19.9mV{\pm}0.8$ (n=116) to $-8.5mV{\pm}1.4$ (n=74) and decreased proliferation of 253J cells, compared to negative control siRNA. 253J cells treated with TREK2 siRNA showed a significant increase in the expression of cell cycle boundary proteins p21 and p53 and also a remarkable decrease in protein expression of cyclins D1 and D3. Taken together, the TREK2 channel is present in bladder cancer cell lines and may, at least in part, contribute to cell cycle-dependent growth.

• The Korean Journal of Physiology and Pharmacology
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• v.7 no.4
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• pp.231-238
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• 2003

The present study was undertaken to investigate the effect of bradykinin on secretion of catecholamines (CA) evoked by stimulation of cholinergic receptors and membrane depolarization from the isolated perfused model of the rat adrenal glands, and to elucidate its mechanism of action. Bradykinin $(3{\times}10^{-8}M)$ alone produced a weak secretory response of the CA. however, the perfusion with bradykinin $(3{\times}10^{-8}M)$ into an adrenal vein of the rat adrenal gland for 90 min enhanced markedly the secretory responses of CA evoked by ACh $(5.32{\times}10^{-3}M)$, excess $K^+$ ($5.6{\times}10^{-2}M$, a membrane depolarizer), DMPP ($10^{-4}$ M, a selective neuronal nicotinic agonist) and McN-A-343 ($10^{-4}$ M, a selective M1-muscarinic agonist). Moreover, bradykinin ($3{\times}10^{-8}$ M) in to an adrenal vein for 90 min also augmented the CA release evoked by BAY-K-8644, an activator of the dihydropyridine L-type $Ca^{2+}$ channels. However, in the presence of $(N-Methyl-D-Phe^7)$-bradykinin trifluoroacetate salt $(3{\times}10^{-8}M)$, an antagonist of $BK_2$-bradykinin receptor, bradykinin no longer enhanced the CA secretion evoked by Ach and high potassium whereas the pretreatment with Lys-$(des-Arg^9,\;Leu^9)$-bradykinin trifluoroacetate salt $(3{\times}10^{-8}M)$, an antagonist of $BK_1$-bradykinin receptor did fail to affect them. Furthermore, the perfusion with bradykinin $(3{\times}10^{-6}M)$ into an adrenal vein of the rabbit adrenal gland for 90 min enhanced markedly the secretory responses of CA evoked by excess $K^+$ $(5.6{\times}10^{-2}M)$. Collectively, these experimental results suggest that bradykinin enhances the CA secretion from the rat adrenal medulla evoked by cholinergic stimulation (both nicotininc and muscarinic receptors) and membrane depolarization through the activation of $B_2$-bradykinin receptors, not through $B_1$-bradykinin receptors. This facilitatory effect of bradykinin seems to be associated to the increased $Ca^{2+}$ influx through the activation of the dihydropyridine L-type $Ca^{2+}$ channels.

• The Korean Journal of Pharmacology
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• v.22 no.2
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• pp.151-156
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• 1986

There are some evidence for the presence of more than one type of calcium channels. To investigate whether organic calcium antagonist sensitive calcium channels exist in the isolated sarcolemmal membrane, we prepared high KCl-loaded sarcolemmal vesicle from the procine small instine, and induced calcium transport by high $K^+$ concentration or by electrical stimulation after preincubation of KCl-loaded vesicle in the low potassium solution. Calcium transport induced by high $K^+$ concentration (84.7mM) was significantly increased (p<0.05), compared with that by low $K^+$ concentration (2.08 mM), and not inhibited by diltiazem $(10^{-6}\;M)$. Calcium transport was inactivated with time. By continuous electrical stimulation (3V, 15Hz, 25m see), calcium transport was markedly increased, and inhibited significantly by dilltiazem $(10^{-6}\;M)$ and nifedipine $(10^{-6}\;M)$ (p<0.005), compared with the value of control without electrical stimulation. Calcium transport by electrical stimulation was not inactivated with time for at least 2 min. From these results, it was concluded that there was organic calcium antagonist sensitive channel in the isolated intestinal sarcolemma membrane, which was activated by electrical stimulation.

• Journal of Korean Neurosurgical Society
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• v.29 no.11
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• pp.1429-1436
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• 2000

Objectives : This study was performed in cultured rat hippocampal neurons to investigate the acute electrophysiological features of ionotropic glutamate receptors which act as a major excitatory neurotransmitter in mammalian brain. Method : Glutamate receptor agonists were applied into the bath solution embedding in whole-cell patch-clamp recording of single hippocampal neuron. Results : In voltage-clamped at -60mV and the presence of 1mmol $Mg^{2+}$, extracellulary applied NMDA did not induce any inward current. Both the elimination of $Mg^{2+}$ and addition of glycine in bath, however, elicited a NMDAinduced inward current. $Mg^{2+}$ block current was increased gradually in more negative potentials from -30mV, showing a negative slope in I-V plot with $Mg^{2+}$. Glutamate-induced current represented an outward rectification. A non-NMDA receptor component occupied about 40% of glutamate-induced current in the voltage range of -80mV to +60mV. Conclusion : Present study suggests that glutamate activates acutely the non-NMDA receptors which induces an inward current in the level of resting membrane potential. This makes the membrane potential increase and can activate the NMDA receptors that permit calcium influx against $Mg^{2+}$ block. At the depolarized state of neuron, there may be recovery mechanisms of membrane potential to repolarize irrespective of voltage-dependent potassium channels in the hippocampal neurons.