• Molecules and Cells
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• v.22 no.1
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• pp.65-69
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• 2006

In murine gastrointestinal myocytes muscarinic stimulation activates nonselective cation channels via a G-protein and $Ca^{2+}$-dependent pathway. We recorded inward cationic currents following application of carbachol ($I_{CCh}$) to murine gastric myocytes held at -60 mV, using the whole-cell patch-clamp method. The properties of the inward cationic currents were similar to those of the nonselective cation channels activated by muscarinic stimulation in other gastrointestinal smooth muscle cells. CCh-induced $I_{CCh}$ and spontaneous decay of $I_{CCh}$ (desensitization of $I_{CCh}$) occurred. Unlike the situation in guinea pig gastric myocytes, desensitization was not affected by varying $[EGTA]_i$. Pretreatment with the PLC inhibitor (U73122) blocked the activation of $I_{CCh}$, and desensitization of $I_{CCh}$ was attenuated in PLC ${\beta}_1$ knock-out mice. These results suggest that the desensitization of $I_{CCh}$ in murine gastric myocytes is not due to a pathway dependent on intracellular $Ca^{2+}$ but to the PLC ${\beta}_1$ pathway.

• The Korean Journal of Physiology and Pharmacology
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• v.6 no.1
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• pp.47-55
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• 2002

To identify the presence of inwardly rectifying $K^+$ channels and its characteristics, membrane currents were measured using a whole-cell patch clamp from isolated gastric myocytes of guinea-pig. Change of external $K^+$ concentration from 5 to 90 mM induced an inward current at a holding potential of -80 mV. The high $K^+-induced$ inward current was blocked by $Ba^{2+}$ and $Cs^+,$ but not by glibenclamide. With 90 mM $K^+$ in bath, the $Ba^{2+}-$ and $Cs^+-sensitive$ currents showed strong inward rectification. Ten mM TEA weakly blocked the inward current only at potentials more negative than -50 mV. With 90 mM $K^+$ in bath, hyperpolarizing step pulses from -10 mV induced inward currents, which were inactivated at potentials more negative than -70 mV. Reduction of external $K^+$ to 60 mM decreased the amplitudes of the currents and shifted the reversal potential to more negative potential. The inactivation of inward $K^+$ current at negative clamp voltage was not affected by removing external $Na^+.$ These results suggest that the inwardly rectifying $K^+$ channels may exist in gastric smooth muscle.

• The Korean Journal of Physiology
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• v.28 no.2
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• pp.143-150
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• 1994

The whole-cell mode of the patch clamp technique was used to study $Ca^{2+}-activated\;Cl^-\;current$ $(I_{Cl_{Ca}})$ in gastric antral myocytes. Extracellular application of caffeine evoked $Ca^{2+}-activated\;current$. In order to isolate the chloride current from background current, all known systems were blocked with specific blockers. The current-voltage relationship of caffeine-induced current showed outward rectification and it reversed at around $E_{Cl^-}$. The shift of reversal potential upon the alteration of external and internal chloride concentrations was well fitted with results which were calculated by the Nernst equation. Extracellular addition of N-phenylanthranilic acid and niflumic acid which are known anion channel blockers abolished the caffeine induced current. Intracellular application of a high concentration of EGTA also abolished this current. Application of c-AMP, c-GMP, heparin, or $AIF^-_4$ made no remarkable changes to this current. Sodium replacement with the impermeable cation N-methylglucamine or with $Cd^{2+}$ rarely affected this current. From the above results it is suggested that the caffeine induced current was a $Cl^-$ current and it was activated by intracellular $Ca^{2+}$.

• The Korean Journal of Physiology and Pharmacology
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• v.9 no.2
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• pp.103-108
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• 2005

To study the direct effect of somatostatin (SS) on calcium channel current ($I_{Ba}$) in guinea-pig gastric myocytes, $I_{Ba}$ was recorded by using whole-cell patch clamp technique in single smooth muscle cells. Nicardipine ($1{\mu}M$), a L-type $Ca^{2+}$ channel blocker, inhibited $I_{Ba}$ by $98{\pm}1.9$% (n=5), however $I_{Ba}$ was decreased in a reversible manner by application of SS. The peak $I_{Ba}$ at 0 mV were decreased to $95{\pm}1.5$, $92{\pm}1.9$, $82{\pm}4.0$, $66{\pm}5.8$, $10{\pm}2.9$% at $10^{-10}$, $10^{-9}$, $10^{-8}$, $10^{-7}$, $10^{-5}$ M of SS, respectively (n=3∼6; $mean{\pm}SEM$). The steady-state activation and inactivation curves of $I_{Ba}$ as a function of membrane potentials were well fitted by a Boltzmann equation. Voltage of half-activation ($V_{0.5}$) was $-12{\pm}0.5$ mV in control and $-11{\pm}1.9$ mV in SS treated groups (respectively, n=5). The same values of half-inactivation were $-35{\pm}1.4$ mV and $-35{\pm}1.9$ mV (respectively, n=5). There was no significant difference in activation and inactivation kinetics of $I_{Ba}$ by SS. Inhibitory effect of SS on $I_{Ba}$ was significantly reduced by either dialysis of intracellular solution with $GDP_{\beta}S$, a non-hydrolysable G protein inhibitor, or pretreatment with pertussis toxin (PTX). SS also decreased contraction of guinea-pig gastric antral smooth muscle. In conclusion, SS decreases voltage-dependent L-type calcium channel current ($VDCC_L$) via PTXsensitive signaling pathways in guinea-pig antral circular myocytes.

• Proceedings of the Korean Biophysical Society Conference
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• 1997.07a
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• pp.17-17
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• 1997

We investigated the relationship between the voltage-operated calcium channel current and the corresponding [Ca$^{2＋}$]i change (Ca$^{2＋}$-transient) in guinea-pig gastric myocyte. Fluorescence microspectroscopy was combined with conventional whole-cell patch clamp technique and fura-2 (80 $\mu$M) was added into the CsCl-rich pipette solution.(omitted)

• The Korean Journal of Physiology
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• v.27 no.2
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• pp.139-150
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• 1993

We have reported that dopamine potentiates spontaneous contractions dose-dependently in guinea-pig antral circular muscle strips (Hwang et al, 1991). To clarify the underlying excitatory mechanism of dopamine on the gastric smooth muscle, the effects of dopamine on voltage-dependent $Ca^{2+}\;currents\;and\;Ca^{2+}\;-dependent\;K^+\;currents$ were observed in enzymatically dispersed guinea-pig gastric myocytes using the whole-cell voltage-clamp technique. Experiments were also done using isometric tension recording and conventional intracellular microelectrode techniques. 1) The effect of dopamine on the spontaneous contraction of antral circular muscle strips of the guinea-pig was excitatory in a dose-dependent manner, and was blocked by phentolamine, an ${\alpha}-adrenoceptor$ blocker. 2) The slow waves were not changed by dopamine. 3) The voltage-operated inward $Ca^{2+}$ current was not influenced by dopamine. 4) The $Ca^{2+}\;-dependent\;K^+$ outward current, which might reflect the changes of intracellular calcium concentration, was enhanced by dopamine. This effect was abolished by phentolamine. 5) The enhancing effect of dopamine on the $Ca^{2+}\;-dependent\;K^+$ current disappeared with heparin which is known to block the action of $InsP_3$. From these results, it is suggested that dopamine acts via $InsP_3-mediated\;Ca^{2+}$ mobilization from intracellular stores and such action potentiates the spontaneous contraction of guinea-pig gastric smooth muscle.

• The Korean Journal of Physiology and Pharmacology
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• v.1 no.4
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• pp.435-443
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• 1997

We employed the whole-cell patch clamp technique to investigate the effects of arachidonic acid (AA) on barium inward current through the L-type calcium channels ($I_{Ba}$) and on osmotic stretch-induced increase of $I_{Ba}$ in guinea-pig antral gastric myocytes. Under isosmotic condition, AA inhibited $I_{Ba}$ in a dose-dependent manner to $91.1{\pm}1.4,\;72.0{\pm}3.2,\;46.0{\pm}1.8,\;and\;20.3{\pm}2.3%$ at 1, 5, 10, 30 mM, respectively. The inhibitory effect of AA was not affected by 10 ${\mu}M$ indomethacin, a cyclooxygenase inhibitor. Other unsaturated fatty acids, linoleic acid (LA) and oleic acid (OA) were also found to suppress $I_{Ba}$ but stearic acid (SA), a saturated fatty acid, had no inhibitory effect on $I_{Ba}$. The potency sequence of these inhibitory effects was AA ($79.7{\pm}2.3%$) ＞ LA ($43.1{\pm}2.7%$) ＞ OA ($14.2{\pm}1.1%$) at 30 ${\mu}M$. On superfusing the myocyte with hyposmotic solution (214 mOsm) the amplitude of $I_{Ba}$ at 0 mV increased ($38.0{\pm}5.5%$); this increase was completely blocked by pretreatment with 30 mM AA, but not significantly inhibited by lower concentrations of AA (1, 5 and 10 ${\mu}M$) (P＞0.05). Unsaturated fatty acids shifted the steady-state inactivation curves of $I_{Ba}$ to the left; the extent of shift caused by AA was greater than that caused by LA. The activation curve was not affected by AA or LA. The results suggest that AA and other unsaturated fatty acids directly modulate L-type calcium channels and AA might modulate the hyposmotic stretch- induced increase of L-type calcium channel current in guinea-pig gastric smooth muscle.

• The Korean Journal of Physiology and Pharmacology
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• v.2 no.1
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• pp.85-93
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• 1998

ATP-sensitive $K^+$ channels ($K_{ATP}$) were not identified in gastric smooth muscle cells. However, in tension recording of intact gastric circular muscle, lemakalim of $K_{ATP}$ channels opener in other tissues suppressed mechanical contractions and this effect was blocked by glibenclamide, a specific inhibitor of $K_{ATP}$ channels. The aims of this study were to investigate whether $K_{ATP}$ channels exist in gastric smooth muscle of guinea-pig and to know its physiological role. Whole cell $K^+$ currents activated by lemakalim were recorded from freshly isolated cells with a 0.1 mM ATP, 140 mM KCl pipette solutions. Lemakalim (10 ${\mu}M$) increased inward currents of $-224{\pm}34$ pA (n=13) at -80 mV of holding potential in bath solution contained 90 mM $K^+$. Bath-applied glibenclamide (10 ${\mu}M$) inhibited the lemakalim-activated inward currents by $91{\pm}6%$ (n=5). These lemakalim-activated inward currents were reduced by increased intracellular ATP from 0.1 to 3 mM ($-41{\pm}12$ pA) (n=5). The reversal potential of the glibenclamide- sensitive inward currents was $-5.2{\pm}2.4$ mV (n=3) in external 90 mM $K^+$ and shifted to $-14.8{\pm}3.6$ mV (n=3) in external 60 mM $K^+$, which close to equilibrium potential of $K^+$ ($E_K$). External barium and cesium inhibited the lemakalim-activated inward currents dose-dependently. The half-inhibitory dose ($IC_{50}$) of barium and cesium were 2.3 ${\mu}M$ (n=5) and 0.38 mM (n=4), respectively. 10 mM tetraethylammonium (TEA) also inhibited the lemakalim-activated inward currents by $66{\pm}15%$ (n=5). Both substance P (SP) (5 ${\mu}M$) and acetylcholine (ACh) (5 ${\mu}M$) inhibited lemakalim-activated inward currents. These results suggest that $K_{ATP}$ channels exist in the gastric smooth muscle and its modulation by neurotransmitters may play an important role in regulating gastric motility.

• The Korean Journal of Physiology and Pharmacology
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• v.2 no.3
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• pp.353-359
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• 1998

In gastrointestinal smooth muscle, muscarinic stimulation by carbachol (CCh) activates nonselective cation channel current ($I_{CCh}$) which is facilitated by intracellular [$Ca^{2+}$] increase. Caffeine is widely used in experiments to mobilize $Ca^{2+}$ from intracellular stores. This study shows a strong inhibitory effect of caffeine on $I_{CCh}$ in guinea-pig gastric myocyte. In this study, the underlying mechanism of the inhibitory effect of caffeine was investigated. $I_{CCh}$ was completely suppressed by the addition of caffeine (10 mM) to the superfusing solution. Inhibition of $I_{CCh}$ by caffeine was not related to the intracellular cAMP accumulation which was expected from the phosphodiesterase-inhibiting effect of caffeine. The blockade of $InsP_3-induced$ $Ca^{2+}$ release by heparin had no significant effects on the activation of $I_{CCh}$. When the same cationic current had been induced by intracellular dialysis of $GTP[{\gamma}S]$ in order to bypass the muscarinic receptor, the inhibitory effect of caffeine was significantly attenuated. The results of this study indicate that both intracellular signalling pathways for $I_{CCh}$, proximal and distal to G-protein activation, are suppressed by caffeine. A major inhibition was observed at the proximal level.

• The Korean Journal of Physiology
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• v.27 no.2
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• pp.115-122
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• 1993

There is evidence that noradrenaline enhances spontaneous contractions dose-dependently in guinea-pig antral circular muscle. To investigate the mechanism of this excitatory action, slow waves and membrane currents were recorded using conventional microelectrode techniques in muscle strips and the whole cell patch clamp technique in isolated gastric myocytes. On recording slow waves, noradrenaline $(10^{-5}\;M)$ induced the hyperpolarization of the membrane potential, although the shape of the slow waves became tall and steep. Also, spike potentiaIs occurred at the peaks of slow waves. These changes were completely reversed by administration of phentolamine $(10^{-5}\;M),\;an\;{\alpha}-adrenoceptor$ blocker. Noradrenaline-induced hyperpolarization was blocked by apamin $(10^{-7}\;M)$, a blocker of a class of $Ca^{2+}\;-dependent\;K^+$ channels. To investigate the mechanisms for these effects, we performed whole cell patch clamp experiments. Norndrenaline increased voltage-dependent $Ca^{2+}$ currents in the whole range of test potentials. Noradrenaline also increased $Ca^{2+}\;-dependent\;K^+$\;currents, and this effects was abolished by apamin. These results suggest that the increase in amplitude and the generation of spike potentials on slow waves was caused by the activation of voltage-dependent $Ca^{2+}$ channel via adrenoceptors, and hyperpolarization of the membrane potential was mediated by activation of apamin-sensitive $Ca^{2+}\;-dependent\;K^+\;channels$.