• 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.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 and Pharmacology
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• v.17 no.5
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• pp.463-468
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• 2013

Acute hypoxia induces contraction of pulmonary artery (PA) to protect ventilation/perfusion mismatch in lungs. As for the cellular mechanism of hypoxic pulmonary vasoconstriction (HPV), hypoxic inhibition of voltage-gated $K^+$ channel (Kv) in PA smooth muscle cell (PASMC) has been suggested. In addition, our recent study showed that thromboxane $A_2$ ($TXA_2$) and hypoxia-activated nonselective cation channel ($I_{NSC}$) is also essential for HPV. However, it is not well understood whether HPV is maintained in the animals exposed to ambient hypoxia for two days (2d-H). Specifically, the associated electrophysiological changes in PASMCs have not been studied. Here we investigate the effects of 2d-H on HPV in isolated ventilated/perfused lungs (V/P lungs) from rats. HPV was almost abolished without structural remodeling of PA in 2d-H rats, and the lost HPV was not recovered by Kv inhibitor, 4-aminopyridine. Patch clamp study showed that the hypoxic inhibition of Kv current in PASMC was similar between 2d-H and control. In contrast, hypoxia and $TXA_2$-activated $I_{NSC}$ was not observed in PASMCs of 2d-H. From above results, it is suggested that the decreased $I_{NSC}$ might be the primary functional cause of HPV disappearance in the relatively early period (2 d) of hypoxia.

• The Korean Journal of Physiology and Pharmacology
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• v.24 no.1
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• pp.101-110
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• 2020

Transient receptor potential canonical 4 (TRPC4) channel is a nonselective calcium-permeable cation channels. In intestinal smooth muscle cells, TRPC4 currents contribute more than 80% to muscarinic cationic current (mIcat). With its inward-rectifying current-voltage relationship and high calcium permeability, TRPC4 channels permit calcium influx once the channel is opened by muscarinic receptor stimulation. Polyamines are known to inhibit nonselective cation channels that mediate the generation of mIcat. Moreover, it is reported that TRPC4 channels are blocked by the intracellular spermine through electrostatic interaction with glutamate residues (E728, E729). Here, we investigated the correlation between the magnitude of channel inactivation by spermine and the magnitude of channel conductance. We also found additional spermine binding sites in TRPC4. We evaluated channel activity with electrophysiological recordings and revalidated structural significance based on Cryo-EM structure, which was resolved recently. We found that there is no correlation between magnitude of inhibitory action of spermine and magnitude of maximum current of the channel. In intracellular region, TRPC4 attracts spermine at channel periphery by reducing access resistance, and acidic residues contribute to blocking action of intracellular spermine; channel periphery, E649; cytosolic space, D629, D649, and E687.

• The Korean Journal of Physiology and Pharmacology
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• v.5 no.1
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• pp.71-78
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• 2001

Capsaicin, a pungent ingredient of hot pepper, elicits an intense burning pain when applied cutaneously and intradermally. Activation of capsaicin-gated channel in C-type dorsal root ganglion (DRG) neurons produces nonselective cationic currents. Although electrophysiological and biochemical properties of capsaicin-activated current $(I_{CAP})$ were studied, the regulatory mechanism and intracellular signaling pathway are still unclear. In the present study, we investigated the modulations of $I_{CAP}$ by DAMGO $({\mu}-opioid\;agonist)$ and cholecystokinin octapeptide (CCK-8). In 18 out of 86 cells, the amplitude of $I_{CAP}$ was significantly increased by DAMGO and completely reversed after washout, while $I_{CAP}$ was decreased by DAMGO in 25 cells. In 43 cells, DAMGO had no effect on $I_{CAP}$. Mean action potential duration was significantly different between 'increased-by-DAMGO' group and 'decreased-by-DAMGO' group. Mean amplitudes of $I_H$ were not significantly different between both groups. CCK-8 reversibly enhanced the amplitude of $I_{CAP}$ (5/13). DAMGO also increased $I_{CAP}$ amplitude significantly in the same cells. The amplitude of $I_{CAP}$ was increased in additive manner by combined applications of DAMGO and CCK-8 in these cells. These results suggest that DAMGO and CCK-8 can either increase or decrease $I_{CAP}$ presumably depending on the subtypes of DRG cells and classified by electrophysiological properties.