• The Korean Journal of Physiology
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• v.28 no.1
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• pp.51-59
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• 1994

This study was carried out to elucidate the excitatory mechanisms of Substance P in the antral circular muscle, using isometric contraction recording, conventional microelectrode method and whole-cell patch clamp technique. Substance P produced tonic and phasic contractions in a dose-dependent manner and depolarized membrane potential with increased amplitude of slow waves in muscle strips. Voltage-dependent $Ca^{2+}$ currents were increased by the application of Substance P from a holding potential of -60mV to 50mV in 10mV steps and this effect was blocked by the addition of an antagonist. Also Substance P increased transient and spontaneous oscillatory $K^+$ outward currents. The enhanced outward currents were abolished by apamin in dispersed single cells. These results suggest that the depolarization of membrane potential by Substance P activates voltage-dependent $Ca^{2+}$ channels, which represents an excitatory response in the antral circular muscle and led to an increase in $Ca^{2+}\;activated\;K^+\;currents$.

• The Korean Journal of Physiology and Pharmacology
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• v.2 no.5
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• pp.549-553
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• 1998

Using the planar lipid bilayer method, we investigated the effect of d-tubocurarine (dTC) on the extracellular side of large-conductance $Ca^{2+}-activated\;K^+$ channel from rat brain. When the initial open probability (Po) of the channel was relatively high, dTC decreased channel activity in a concentration dependent manner. In contrast, when the initial Po was lower, sub-micro molar dTC increased channel activity by destabilizing the closed states of the channel. Further addition of dTC up to micro molar range decreased channel activity. This dual effect of dTC implicates that there exist at least two different binding sites for dTC.

• The Korean Journal of Physiology and Pharmacology
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• v.9 no.1
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• pp.29-35
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• 2005

To prove the buffering contribution of mitochondria to the increase of intracellular $Ca^{2+}$ level ($[Ca^{2+}]_i$) via background nonselective cation channel (background NSCC), we examined whether inhibition of mitochondria by protonophore carbonylcyanide m-chlorophenylhydrazone (CCCP) affects endothelial $Ca^{2+}$ entry and $Ca^{2+}$ buffering in freshly isolated rabbit aortic endothelial cells (RAECs). The ratio of fluorescence by fura-2 AM ($R_{340/380}$) was measured in RAECs. Biological state was checked by application of acetylcholine (ACh) and ACh ($10{\mu}M$) increased $R_{340/380}$ by $1.1{\pm}0.15$ ($mean{\pm}S.E.$, n=6). When the external $Na^+$ was totally replaced by $NMDG^+$, $R_{340/380}$ was increased by $1.19{\pm}0.17$ in a reversible manner (n=27). $NMDG^+$-induced $[Ca^{2+}]_i$ increase was followed by oscillatory decay after $[Ca^{2+}]_i$ reached the peak level. The increase of $[Ca^{2+}]_i$ by $NMDG^+$ was completely suppressed by replacement with $Cs^+$. When $1{\mu}M$ CCCP was applied to bath solution, the ratio of $[Ca^{2+}]_i$ was increased by $0.4{\pm}0.06$ (n=31). When $1{\mu}M$ CCCP was used for pretreatment before application of $NMDG^+$, oscillatory decay of $[Ca^{2+}]_i$ by $NMDG^+$ was significantly inhibited compared to the control (p＜0.05). In addition, $NMDG^+-induced$ increase of $[Ca^{2+}]_i$ was highly enhanced by pretreatment with $2{\mu}M$ CCCP by $320{\pm}93.7$%, compared to the control ($mean{\pm}S.E.$, n=12). From these results, it is concluded that mitochondria might have buffering contribution to the $[Ca^{2+}]_i$ increase through regulation of the background NSCC in RAECs.

• The Korean Journal of Physiology and Pharmacology
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• v.6 no.4
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• pp.207-214
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• 2002

The present study was designed to clarify whether tacrine affects the release of catecholamines (CA) from the isolated perfused model of rat adrenal gland or not and to elucidate the mechanism of its action. Tacrine $(3{\times}10^{-5}{\sim}3{\times}10^{-4}\;M)$ perfused into an adrenal vein for 60 min inhibited CA secretory responses evoked by ACh $(5.32{\times}10^{-3}\;M),$ DMPP (a selective neuronal nicotinic agonist, $10^{-4}$ M for 2 min) and McN-A-343 (a selective muscarinic M1-agonist, $10^{-4}$ M for 2 min) in relatively dose- and time- dependent manners. However, tacrine failed to affect CA secretion by high $K^+\;(5.6{\times}10^{-2}\;M).$ Tacrine itself at concentrations used in the present experiments did not also affect spontaneous CA output. Furthermore, in the presence of tacrine $(10^{-4}\;M),$ CA secretory responses evoked by Bay-K-8644 (an activator of L-type $Ca^{2+}$ channels, $10^{-4}\;M),$ but not by cyclopiazonic acid (an inhibitor of cytoplasmic $Ca^{2+}-ATPase,\;10^{-4}\;M),$ was relatively time-dependently attenuated. Also, physostigmine $10^{-4}\;M),$ given into the adrenal gland for 60 min, depressed CA secretory responses evoked by ACh, McN-A-343 and DMPP while did not affect that evoked by high $K^+.$ Collectively, these results obtained from the present study demonstrate that tacrine greatly inhibits CA secretion from the perfused rat adrenal gland evoked by stimulation of cholinergic (both nicotinic and muscarinic) receptors, but does fail to affect that by direct membrane-depolarization. It is suggested that this inhibitory effect of tacrine may be exerted by blocking both the calcium influx into the rat adrenal medullary chromaffin cells without $Ca^{2+}$ release from the cytoplasmic calcium store, that is relevant to the cholinergic blockade. Also, the mode of action between tacrine and physostigmine in rat adrenomedullary CA secretion seems to be similar.

• The Korean Journal of Physiology and Pharmacology
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• v.4 no.5
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• pp.403-408
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• 2000

The outward currents elicited in hamster eggs by depolarizing pulses were studied. The currents appeared to comprise at least two components, a transient outward component $(I_{to})$ and a steady-state outward component $(I_{\infty}).\;I_{to}$ was transiently followed by the cessation of inward $Ca^{2+}$ current $(I_{Ca}),$ and its current-voltage (I-V) relation was a mirror image of that of $(I_{Ca}).$ Either blockade of $(I_{Ca})$ by $Co^{2+}$ or replacement of $Ca^{2+}$ with $Sr^{2+}$ abolished $I_{to}$ without change in $I_{\infty}.$ Intracellular EGTA (10 mM) inhibited $I_{to}$ but not $I_{\infty}.$ suggesting strongly that generation of $I_{to}$ requires intracellular $Ca^{2+}.$ Apamin (1 nM) abolished selectively $I_{to},$ indicatingthat $I_{to}$ is $Ca^{2+}-dependent\;K^+$ current. On the other hand, $I_{\infty}$ was $Ca^{2+}-independent.$ Both $I_{to}$ and $I_{\infty}$ were completely inhibited by internal $Cs^+$ and external TEA. The estimated reversal potential of $I_{to}$ was close to the theoretical $E_K.$ Taken together, both outward currents were carried by $K^+$ channels. From these results, $I_{to}$ is likely to be a current responsible for the hyperpolarizing responses seen in hamster eggs at fertilization.

• Proceedings of the Korean Biophysical Society Conference
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• 2002.06b
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• pp.36-36
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• 2002

In the present study, we investigated effects of extracellular zinc (Zn$\^$2＋/) on T-type Ca$\^$2＋/ channel isoforms (${\alpha}$lG, ${\alpha}$lH, and ${\alpha}$lI) stably expressed in HEK 293 cells. Ca$\^$2＋/ currents were measured using 10 mM Ca$\^$2＋/ as a charge carrier under whole cell-ruptured patch configuration. Zn$\^$2＋/ blocked the ${\alpha}$lH currents with a 100- and 200-fold higher potency (IC$\sub$50/ = 2.5 ${\mu}$M) when compared with those for blockade of the ${\alpha}$1G and ${\alpha}$1I currents, respectively.(omitted)

• Archives of Pharmacal Research
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• v.28 no.8
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• pp.914-922
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• 2005

The present study was designed to examine the effects of green tea extract (CUMC6335) and epigallocatechin gallate (EGCG) on secretion of catecholamines (CA) in the isolated perfused rabbit adrenal gland. In the presence of CUMC6335 $(200 {\mu}g/mL)$ into an adrenal vein for 60min, CA secretory responses evoked by ACh (5.32 mM), high $K^+$ (56 mM), DMPP $(100{\mu}M \;for\;2min)$, and Bay-K-8644 $(10{\mu}M\;for\;4min)$ from the isolated perfused rabbit adrenal glands were greatly inhibited in a time-dependent fashion. However, EGCG $(10{\mu}g/mL)$ did not affect CA release evoked by ACh, high $K^+$, and Bay-K-8644. CUMC6335 itself failed to affect basal catecholamine output. Taken together, these results demonstrate that CUMC6335 inhibits CA secretion evoked by stimulation of cholinergic nicotinic receptors, as well as the direct membrane depolarization from the isolated perfused rabbit adrenal gland. It is thought that this inhibitory effect of CUMC6335 may be due at least in part to the blocking action of the L-type dihydropyridine calcium channels in the rabbit adrenomedullary chromaffin cells, which is relevant to the cholinergic nicotinic blockade. It seems that there is a big difference in mode of action between CUMC6335 and EGCG.

• BMB Reports
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• v.50 no.6
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• pp.323-328
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• 2017

Lysophosphatidylcholine (LPC) is a major phospholipid component of oxidized low-density lipoprotein (ox-LDL) and is implicated in its atherogenic activity. This study investigated the effects of LPC on cell viability, intracellular calcium homeostasis, and the protective mechanisms of chlorogenic acid (CGA) in human umbilical vein endothelial cells (HUVECs). LPC increased intracellular calcium ($[Ca^{2+}]_i$) by releasing $Ca^{2+}$ from intracellular stores and via $Ca^{2+}$ influx through store-operated channels (SOCs). LPC also increased the generation of reactive oxygen species (ROS) and decreased cell viability. The mRNA expression of Transient receptor potential canonical (TRPC) channel 1 was increased significantly by LPC treatment and suppressed by CGA. CGA inhibited LPC-induced $Ca^{2+}$ influx and ROS generation, and restored cell viability. These results suggested that CGA inhibits SOC-mediated $Ca^{2+}$ influx and ROS generation by attenuating TRPC1 expression in LPC-treated HUVECs. Therefore, CGA might protect endothelial cells against LPC injury, thereby inhibiting atherosclerosis.

• The Korean Journal of Physiology and Pharmacology
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• v.9 no.4
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• pp.223-230
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• 2005

The purpose of the present study was to examine the effect of naltrexone, an opioid antagonist, on secretion of catecholamines (CA) evoked by cholinergic nicotinic stimulation and membrane-depolarization from the isolated perfused rat adrenal gland and to establish the mechanism of its action. Naltrexone $(3{\times}10^{-6}M)$ perfused into an adrenal vein for 60 min produced time-dependent inhibition in CA secretory responses evoked by ACh $(5.32{\times}10^{-3}M)$ , high $K^+$ $(5.6{\times}10^{-2}M)$ , DMPP ($10^{-4}$ M) and McN-A-343 $(10^{-4}M)$ . Naltrexone itself did also fail to affect basal CA output. In adrenal glands loaded with naltrexone $(3{\times}10^{-6}M)$ , the CA secretory responses evoked by Bay-K-8644, an activator of L-type $Ca^{2+}$ channels and cyclopiazonic acid, an inhibitor of cytoplasmic $Ca^{2+}-ATPase$, were also inhibited. However, in the presence of met-enkephalin $(5{\times}10^{-6}M)$ , a well-known opioid agonist, the CA secretory responses evoked by ACh, high $K^+$, DMPP, McN-A-343, Bay-K-8644 and cyclopiazonic acid were also significantly inhibited. Collectively, these experimental results demonstrate that naltrexone inhibits greatly CA secretion evoked by stimulation of cholinergic (both nicotinic and muscarinic) receptors as well as that by membrane depolarization. It seems that this inhibitory effect of naltrexone does not involve opioid receptors, but might be mediated by blocking both the calcium influx into the rat adrenal medullary chromaffin cells and the uptake of $Ca^{2+}$ into the cytoplasmic calcium store, which are at least partly relevant to the direct interaction with the nicotinic receptor itself.

• International Journal of Oral Biology
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• v.31 no.2
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• pp.45-51
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• 2006

R-type($Ca_v2.3$) calcium channel contributes to pain sensation in peripheral sensory neurons. Six isoforms of $Ca_v2.3$ that result from combinations of presence or deletion of three inserts(insert I and insert in the II-III loop, and insert III in N-terminal regions) have been demonstrated to be present in different mammalian tissues. However, the molecular basis of $Ca_v2.3$ in trigeminal ganglion(TG) neurons is not known. In the present study, we determined which isoforms of $Ca_v2.3$ are expressed in rat TG neurons using the RT-PCR analysis. Whole tissue RT-PCR analyses revealed that only two isoforms, $Ca_v2.3a$ and $Ca_v2.3e$, were present in TG neurons. From single-cell RT-PCR, we found that $Ca_v2.3e$ rather than $Ca_v2.3a$ was the major isoform expressed in TG neurons, and $Ca_v2.3e$ was preferentially detected in small-sized neurons that express nociceptive marker, transient receptor potential vanilloid 1(TRPV1). Our results suggest that $Ca_v2.3e$ in trigeminal neurons may be a potential target for the pain treatment.