• The Korean Journal of Physiology and Pharmacology
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• v.13 no.5
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• pp.393-400
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• 2009

NO released by myenteric neurons controls the off contraction induced by electrical field stimulation (EFS) in distal esophageal smooth muscle, but in the presence of nitric oxide synthase (NOS) inhibitor, L-NAME, contraction by EFS occurs at the same time. The authors investigated the intracellular signaling pathways related with G protein and ionic channel EFS-induced contraction using cat esophageal muscles. EFS-induced contractions were significantly suppressed by tetrodotoxin ($1\;{\mu}M$) and atropine ($1\;{\mu}M$). Furthermore, nimodipine inhibited both on and off contractions by EFS in a concentration dependent meaner. The characteristics of 'on' and 'off contraction and the effects of G-proteins, phospholipase, and $K^+$ channel on EFS-induced contraction in smooth muscle were also investigated. Pertussis toxin (PTX, a $G_i$ inactivator) attenuated both EFS-induced contractions. Cholera toxin (CTX, $G_s$ inactivator) also decreased the amplitudes of EFS-induced off and on contractions. However, phospholipase inhibitors did not affect these contractions. Pinacidil (a $K^+$ channel opener) decreased these contractions, and tetraethylammonium (TEA, ${K^+}_{Ca}$ channel blocker) increased them. These results suggest that EFS-induced on and off contractions can be mediated by the activations Gi or Gs proteins, and that L-type $Ca^{2+}$ channel may be activated by G-protein ${\alpha}$ subunits. Furthermore, ${K^+}_{Ca^-}$ channel involve in the depolarization of esophageal smooth muscle. Further studies are required to characterize the physiological regulation of $Ca^{2+}$ channel and to investigate the effects of other $K^+$ channels on EFS-induced on and off contractions.

• The Korean Journal of Physiology
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• v.24 no.1
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• pp.39-49
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• 1990

It has been reported that bombesin induces contraction of the smooth muscle of the gastrointestinal tract. Thus, the present investigation was undertaken to see an influence of bombesin on electrical activity of the gastric smooth muscle, since electrical activity is associated with contractile activity in the smooth muscle of the stomach. Smooth muscle strips $(5\;{\times}\;1.5\;cm)$ that included the corpus and antrum were prepared from the ventral and dorsal portion of the feline stomach along the greater curvature. Circular muscle strips $(1\;{\times}\;0.3\;cm)$ of the corpus were also obtained. Electrical activity of the corpus and antrum of the muscle strip was monophasically recorded by using Ag-AgCl capillary electrodes placed on the circular muscle layer. Contractile activity of the circular muscle strip was also recorded. The recordings were performed in Krebs-Ringer solution that was continuously aerated with $O_{2}$ containing 5% $Co_{2}$, and kept at $36^{\circ}C$. Dose-related responses of electrical activity and contractility to bombesin was studied after frequency of slow waves and contraction of each strip reached to a steady state. An action of $D-leu^{13}-{\psi}\;(CH_{2}NH)-D-leu^{14}-bombesin,\;D-pro^{2}-D-trp^{7,9}-substance\;P$, tetrodotoxin, hexamethonium, atropine, phentolamine or propranolol on the effect of bombesin was also observed. 1) Bombesin increased frequency of slow waves and contractions dose-dependently at concentrations from $10^{-9}\;M\;to\;3\;{\times}\;10^{-8}\;M$. 2) The bombesin analogue at a concentration of $3\;{\times}\;10^{-7}\;M$ antagonized the effect of bombesin on frequency of slow waves. 3) The effect of bombesin on frequency of slow waves was inhibited by tetrodotoxin $(10^{-6}\;M)$ and hexamethonium $(10^{-3}\;M)$ but unaffected by atropine $(10^{-6}\;M)$, phentolamine $(10^{-5}\;M)$ and propranolol $(10^{-5}\;M)$. 4) The effect of bombesin on frequency of slow waves was blocked by the substance P analogue at a concentration of $10^{-5}\;M$. 5) Substance P at a concentration of $10^{-5}\;M$ failed to change frequency of slow waves. It is concluded from the above results that bombesin increases the frequency of slow waves as well as contractions of the smooth muscle strip from the feline stomach, and the effect of bombesin might be mediated by non-cholinergic or non-adrenergic mechanism at neuromuscular junction. However, enteric nerves that have substance P as a neurotransmitter do not appear to participate in the action of bombesin on frequency of slow waves.

• Korean Journal of Veterinary Research
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• v.35 no.2
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• pp.279-285
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• 1995

To characterize non-adrenergic non-cholinergic(NANC) nerve mediated contractile responses in circular smooth muscle of bovine reticular groove, we investigated NANC relaxation and contraction induced by electric field stimulation to enteric nerves. In the presence of atropine($1{\mu}M$) and guanethidine($50{\mu}M$), electric field stimulation at frequency of 1 to 16Hz(square pulses, 0.5ms duration, 70V) evoked clear-cut relaxations through stimulations. Transient 'rebound contraction' was occured when the stimulus was switched off. All of the responses (relaxation and rebound contraction) were dose-dependently blocked by Nw-nitro-$_{\small{L}}$-arginine methyl ester(L-NAME), an inhibitor of nitric oxide synthesis, and methylene blue, and inhibitor of soluble guanylate cyclase. Tetraethyl ammonium(TEA), a potassium channel blocker, did not block the NANC relaxations.

• Proceedings of the PSK Conference
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• 2003.10b
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• pp.77.3-78
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• 2003

We previously shown that sphingosylphosphorylcholine, a lysophosphatidic acid, produced contraction in isolated single cells of cat ilium. We investigated the mechanism of sphingosine-1-phosphate (S1P)-induced contraction of circular smooth muscle cells in cat esophagus. S1P produced esophageal contraction in a dose dependent manner. The maximal contraction (l0$\^$-7/ M) induced at 1min. Pertusis toxin (PTX) inhibited contraction induced by S1P, suggesting that the contraction is mediated to a PTX-sensitive G-protein. (omitted)

• The Korean Journal of Physiology and Pharmacology
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• v.7 no.6
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• pp.357-362
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• 2003

Carbon monoxide (CO) is low molecular weight oxide gas that is endogenously produced under physiological conditions and interacts with another gas, nitric oxide (NO), to act as a gastrointestinal messenger. The aim of this study was to determine the effects of exogenous CO on L-type calcium channel currents of human jejunal circular smooth muscle cells. Cells were voltage clamped with 10 mM barium ($Ba^{2+}$) as the charge carrier, and CO was directly applied into the bath to avoid perfusion induced effects on the recorded currents. 0.2% CO was increased barium current ($I_{Ba}$) by $15{\pm}2$% ($mean{\pm}S.E.$, p<0.01, n=11) in the cells. To determine if the effects of CO on barium current were mediated through the cGMP pathway, cells were pretreated with 1-H-[1,2,4]oxadiazolo[4,3,-a]quinoxalin-1-one (ODQ, $10{mu}M$), a soluble guanylyl cyclase inhibitor, and exogenous CO (0.2%) had no effect on barium currents in the presence of ODQ ($2{\pm}1$% increase, n=6, p>0.05). CO mediates inhibitory neurotransmission through the nitric oxide pathway. Therefore, to determine if the effects of CO on L-calcium channels were also mediated through NO, cells were incubated with $N^G-nitro-L-arginine$ (L-NNA, 1 mM), a nitric oxide synthase inhibitor. After L-NNA pretreatment, 0.2 % CO did not increase barium current ($4{\pm}2$% increase, n=6, p>0.05). NO donor, SNAP ($20{\mu}M$) increased barium current by $13{\pm}2$% (n=6, p<0.05) in human jejunal smooth muscle cells. These data suggest that CO activates L-type calcium channels through NO/cGMP dependant mechanism.

• The Korean Journal of Physiology
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• v.29 no.2
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• pp.233-241
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• 1995

The nonapeptide bradykinin has been shown to exhibit an array of biological activities including relaxation/contraction of various smooth muscles. In order to investigate the effects of bradykinin on the contractility and the electrical activity of antral circular muscle of guinea-pig stomach, the isometric contraction and membrane potential were recorded. Also, using standard patch clamp technique, the $Ca^{2+}-activated$ K currents were recorded to observe the change in cytosolic $Ca^{2+}$ concentration. $0.4 {\mu}M$ bradykinin induced a triphasic contractile response (transient contraction-transient relaxation-sustained contraction) and this response was unaffected by pretreatment with neural blockers (tetrodotoxin, atropine and guanethidine) or with apamin. Bradykinin induced hyperpolarization of resting membrane potential and enhanced the amplitude of slow waves and spike potentials. The enhancement of spike potentials was blocked by neural blockers. Both the bradykinin-induced contractions and changes in membrane potential were reversed by the selective $B_2$-receptor antagonist $(N{\alpha}-adamantaneacetyl-_{D}-Arg-[Hyp, Thy,_{D}-Phe]-bradykinin)$. In whole-cell patch clamp experiment, we held the membrane potential at -20 mV and spontaneous and transient changes of Ca-activated K currents were recorded. Bradykinin induced a large transient outward current, consistent with a calcium-releasing action of bradykinin front the intracellular calcium pool, because such change was blocked by pretreatment with caffeine. Bradykinin-induced contraction was also blocked by pretreatment with caffeine. From these results, it is suggested that bradykinin induces a calciumrelease and contraction through the $B_{2}$ receptor of guinea-pig gastric smooth muscle. Enhancement of slow wave activity is an indirect action of bradykinin through enteric nerve cells embedded in muscle strip.

• The Korean Journal of Physiology
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• v.28 no.1
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• pp.37-50
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• 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
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• v.13 no.6
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• pp.503-510
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• 2009

To elucidate the mechanism of cyclic nucleotides, such as adenosine 3',5'-cyclic monophosphate (cAMP) and guanosine 3',5'-cyclic monophosphate (cGMP), in the regulation of human gastric motility, we examined the effects of forskolin (FSK), isoproterenol (ISO) and sodium nitroprusside (SNP) on the spontaneous, high $K^+$ and acetylcholine (ACh)-induced contractions of corporal circular smooth muscle in human stomach. Gastric circular smooth muscle showed regular spontaneous contraction, and FSK, ISO and SNP inhibited its phasic contraction and basal tone in a concentration-dependent manner. High $K^+$ (50 mM) produced sustained tonic contraction, and ACh $(10\;{\mu}M)$ produced initial transient contraction followed by later sustained tonic contraction with superimposed phasic contractions. FSK, ISO and SNP inhibited high $K^+$-induced tonic contraction and also ACh-induced phasic and tonic contraction in a reversible manner. Nifedipine $(1\;{\mu}M)$, inhibitor of voltage-dependent L-type calcium current $(VDCC_L)$, almost abolished ACh-induced phasic contractions. These findings suggest that FSK, ISO and SNP, which are known cyclic nucleotide stimulators, inhibit smooth muscle contraction in human stomach partly via inhibition of $VDCC_L$.

• The Korean Journal of Physiology and Pharmacology
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• v.2 no.3
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• pp.361-368
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• 1998

The spontaneous contractions of gastric smooth muscles are regulated by slow waves, which are modulated by both nervous system and humoral agents. This study was designed to examine the effects of prostaglandin $E_2$ ($PGE_2$) on the contractile and electrical activities of antral smooth muscles in guinea-pig stomach, using an intracellular recording technique. To elucidate the underlying mechanism for its effect on contractility, ionic currents were also measured using a whole-cell patch clamp method. The basal tone by $PGE_2$ was variable, whereas the magnitude of phasic contractions was reduced ($19.0{\pm}2.1%$, n=19). The resting membrane potentials were hyperpolarized ($-4.4{\pm}0.5%$ mV, n=10), and plateau potentials were lowered ($-2.9{\pm}0.5%$ mV, n=10). In most cases, however, the initial peak potentials of slow waves were depolarized more by $PGE_2$ than those of control. The frequency of the slows wave was increased from $5.7{\pm}0.2$ cycles/min to $6.5{\pm}0.2$ (n=22). Voltage-operated $Ca^{2+}$ currents were decreased by $PGE_2$ (n=5). Voltage-operated $K^+$ currents, both Ca-dependent and Ca-independent, were increased (n=5). These results suggest that $PGE_2$ plays an important role in the modulation of gastric smooth muscle activities, and its inhibitory effects on the contractility and activities of slow waves are resulted from both decrease of $Ca^{2+}$ currents and increase of $K^+$ currents.

• The Korean Journal of Physiology and Pharmacology
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• v.18 no.5
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• pp.383-390
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• 2014

Gastrointestinal motility consists of phasic slow-wave contractions and the migrating motor complex (MMC). Eupatilin (Stillen$^{(R)}$) has been widely used to treat gastritis and peptic ulcers, and various cytokines and neuropeptides are thought to be involved, which can affect gastrointestinal motility. We performed a study to identify the effects of eupatilin on lower gastrointestinal motility with electromechanical recordings of smooth muscles in the human ileum and colon. Ileum and colon samples were obtained from patients undergoing bowel resection. The tissues were immediately stored in oxygenated Krebs-Ringer's bicarbonate solution, and conventional microelectrode recordings from muscle cells and tension recordings from muscle strips and ileal or colonic segments were performed. Eupatilin was perfused into the tissue chamber, and changes in membrane potentials and contractions were measured. Hyperpolarization of resting membrane potential (RMP) was observed after administration of eupatilin. The amplitude, AUC, and frequency of tension recordings from circular and longitudinal smooth muscle strips and bowel segments of the ileum and colon were significantly decreased after admission of eupatilin. Eupatilin elicited dose-dependent decreases during segmental tension recordings. In conclusion, eupatilin (Stillen$^{(R)}$) showed inhibitory effects on the human ileum and colon. We propose that this drug may be useful for treating diseases that increase bowel motility, but further studies are necessary.