• The Korean Journal of Physiology and Pharmacology
• /
• v.9 no.1
• /
• pp.37-43
• /
• 2005

Our previous report demonstrated that chick myoblasts are equipped with $Ca^{2+}$-permeable stretchactivated channels and $Ca^{2+}-activated$ potassium channels ($K_{Ca}$), and that hyperpolarization-induced by $K_{Ca}$ channels provides driving force for $Ca^{2+}$ influx through the stretch-activated channels into the cells. Here, we showed that acetylcholine (ACh) also hyperpolarized the membrane of cultured chick myoblasts, suggesting that nicotinic acetylcholine receptor (nAChR) may be another pathway for $Ca^{2+}$ influx. Under cell-attatched patch configuration, ACh increased the open probability of $K_{Ca}$ channels from 0.007 to 0.055 only when extracellular $Ca^{2+}$ was present. Nicotine, a nAChR agonist, increased the open probability of $K_{Ca}$ channels from 0.008 to 0.023, whereas muscarine failed to do so. Since the activity of $K_{Ca}$ channel is sensitive to intracellular $Ca^{2+}$ level, nAChR seems to be capable of inducing $Ca^{2+}$ influx. Using the $Ca^{2+}$ imaging analysis, we were able to provide direct evidence that ACh induced $Ca^{2+}$ influx from extracellular solution, which was dramatically increased by valinomycin-mediated hyperpolarization. In addition, ACh hyperpolarized the membrane potential from $-12.5{\pm}3$ to $-31.2{\pm}5$ mV by generating the outward current through $K_{Ca}$ channels. These results suggest that activation of nAChR increases $Ca^{2+}$ influx, which activates $K_{Ca}$ channels, thereby hyperpolarizing the membrane potential in chick myoblasts.

• The Transactions of The Korean Institute of Electrical Engineers
• /
• v.59 no.2
• /
• pp.352-354
• /
• 2010

The effects of Au addition on the structure and the superconducting properties of Bi system bulk have been investigated. Au exists in the metalic form in above materials. It does not affect the formation and structure of the BiSrCaCuO(2223) phase. The superconducting transition temperature Tc does not change for $Bi_{1.7}Pb_{0.3}Sr_2Ca_2Cu_3O$ composite However Au doping can make the grains smaller. Metallic Au can make gathers on the grains boundary and lead to the increment of critical transport current density. The current density of $Bi_{1.7}Pb_{0.3}Sr_2Ca_2Cu_3Au_{0.5}O$ was 1000A/$cm^2$ at liquid nitrogen temperature.

• Proceedings of the Korean Magnestics Society Conference
• /
• 2000.09a
• /
• pp.381-388
• /
• 2000

By applying Current-applied Pressure-Assisted process, we could obtain full dense isotropic and anisotropic NdFeB magnets from rapidly quenched MQP-A powder. The Nd contents are found to play an important role during the CA-press and CA-deformation process. The (BH)$\sub$max/ of CA-pressed and CA-deformed magnets are 131 kJ/㎥(16.5 MGOe) and 352 kJ/㎥(44.2 MGOe), respectively. The texture of CA-deformed anisotropic NdFeB magnets with thickness reduction was investigated by pole figure, and the (006) texture was increase with the increase of thickness reduction. With the increment in thickness reduction from 50%, 60% to 80%, W$\sub$50/ decreases from 76$\^$$^{\circ}$/, 62.5$\^$$^{\circ}$/ to 17$\^$$^{\circ}$/, respectively.

• Applied Chemistry for Engineering
• /
• v.7 no.5
• /
• pp.992-998
• /
• 1996

The $La_{0.8}Ca_{0.2}CoO_3$ prepared by a citrate process was shown to have higher oxygen reduction current density and specific activity than $LaCoO_3$, $La_{0.6}Ca_{0.4}CoO_3$. In the cyclic voltammogram, an oxygen desorption peak of a $La_{0.8}Ca_{0.2}CoO_3$+carbon electrode was larger than that of a only carbon electrode. $La_{0.8}Ca_{0.2}CoO_3$ sintered at $900^{\circ}C$ for 5 hours was shown high oxygen reduction current density because of the particle size distribution and sintering effect.

• The Korean Journal of Physiology and Pharmacology
• /
• v.15 no.5
• /
• pp.279-283
• /
• 2011

Quercetin (3,3',4',5,7-pentahydroxyflavone) is an attractive therapeutic flavonoid for cancer treatment because of its beneficial properties including apoptotic, antioxidant, and antiproliferative effects on cancer cells. However, the exact mechanism of action of quercetin on ion channel modulation is poorly understood in bladder cancer 253J cells. In this study, we demonstrated that large conductance $Ca^{2+}$-activated $K^+$ ($BK_{Ca}$) or MaxiK channels were functionally expressed in 253J cells, and quercetin increased $BK_{Ca}$ current in a concentration dependent and reversible manner using a whole cell patch configuration. The half maximal activation concentration ($IC_{50}$) of quercetin was $45.5{\pm}7.2{\mu}m$. The quercetin-evoked $BK_{Ca}$ current was inhibited by tetraethylammonium (TEA; 5 mM) a non-specific $BK_{Ca}$ blocker and iberiotoxin (IBX; 100 nM) a $BK_{Ca}$-specific blocker. Quercetin-induced membrane hyperpolarization was measured by fluorescence-activated cell sorting (FACS) with voltage sensitive dye, bis (1,3-dibutylbarbituric acid) trimethine oxonol ($DiBAC_4$2(3); 100 nM). Quercetin-evoked hyperpolarization was prevented by TEA. Quercetin produced an antiproliferative effect ($30.3{\pm}13.5%$) which was recovered to $53.3{\pm}10.5%$ and $72.9{\pm}3.7%$ by TEA and IBX, respectively. Taken together our results indicate that activation of $BK_{Ca}$ channels may be considered an important target related to the action of quercetin on human bladder cancer cells.

• YAKHAK HOEJI
• /
• v.56 no.2
• /
• pp.108-115
• /
• 2012

The hyperpolarization-activated current ($I_h$) is an inward cation current activated by hyperpolarization of the membrane potential and plays a role as an important modulator of action potential firing frequency in many excitable cells. In the present study we investigated the effects of extracellular divalent cations on $I_h$ in dorsal root ganglion (DRG) neurons using whole-cell voltage clamp technique. $I_h$ was slightly increased in $Ca^{2+}$-free bath solution. BAPTA-AM did not change the amplitudes of $I_h$. Amplitudes of $I_h$ were decreased by $Ca^{2+}$, $Mg^{2+}$ and $Ba^{2+}$ dose-dependently and voltage-independently. Inhibition magnitudes of $I_h$ by external divalent cations were partly reversed by the concomitant increase of extracellular $K^+$ concentration. Reversal potential of $I_h$ was significantly shifted by $Ba^{2+}$ and $V_{1/2}$ was significantly affected by the changes of extracellular $Ca^{2+}$ concentrations. These results suggest that $I_h$ is inhibited by extracellular divalent cations ($Ca^{2+}$, $Mg^{2+}$ and $Ba^{2+}$) by interfering ion influxes in cultured rat DRG neurons.

• Biomolecules & Therapeutics
• /
• v.17 no.2
• /
• pp.125-132
• /
• 2009

Calbindin-$D_{9k}$ (CaBP-9k), a cytosolic calcium-binding protein, is expressed in a variety of tissues, i.e., the duodenum, uterus, placenta, kidney and pituitary gland. Duodenal CaBP-9k is involved in intestinal calcium absorption, and is regulated at transcriptional and post-transcriptional levels by 1,25-dihydroxyvitamin D3, the hormonal form of vitamin D, and glucocorticoids (GCs). Uterine CaBP-9k has been implicated in the regulation of myometrial action(s) through modulation of intracellular calcium, and steroid hormones appear to be the main regulators in its uterine and placental regulation. Because phenotypes of CaBP-9k-null mice appear to be normal, other calcium-transporter genes may compensate for its gene deletion and physiological function in knockout mice. Previous studies indicate that CaBP-9k may be controlled in a tissue-specific fashion. In this review, we summarize the current information on calcium homeostasis related to CaBP-9k gene regulation by GCs, vitamin D and its receptors, and its molecular regulatory mechanism. In addition, we present related data from our current research.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2001.07a
• /
• pp.1001-1004
• /
• 2001

The (Sr$_{l-x}$Ca$_{x}$)TiO$_3$(SCT) thin films are deposited on Pt-coated electrode(Pt/TiN/SiO$_2$/Si) using RF sputtering method with substitutional contents of Ca. The maximum grain of thin films is obtained by substitution of Ca at 15[mol%]. The dielectric constant was increased -with increasing the substitutional contents of Ca, while it was decreased if the substitutional contents of Ca exceeded over 15[mol%]. The dielectric constant changes almost linearly in temperature ranges of -80~+90[$^{\circ}C$]. The temperature properties of the dielectric loss have a stable value within 0.02 independent of the substitutional contents of Ca. The current-voltage characteristics of SCT15 thin films showed the increasing leakage current as the measuring temperature increases.ses.

• The Korean Journal of Physiology and Pharmacology
• /
• v.5 no.2
• /
• pp.147-156
• /
• 2001

It has been proposed that $Ca^{2+}-activated$ K $(K_{Ca})$ channels play an essential role in vascular tone. The alterations of the properties of coronary $K_{Ca}$ channels have not been studied as a possible mechanism for impaired coronary reserve in cardiac hypertrophy. The present studies were carried out to determine the properties of coronary $K_{Ca}$ channels in normal and hypertrophied hearts. These channels were measured from rabbit coronary smooth muscle cells using a patch clamp technique. The main findings of the present study are as follows: (1) the unitary current amplitudes and the slope conductance of coronary $K_{Ca}$ channels were decreased without changes of the channel kinetics in isoproterenol-induced cardiac hypertrophy; (2) the sensitivity of coronary $K_{Ca}$ channels to the changes of intracellular concentration of $Ca^{2+}$ was reduced in isoproterenol-induced cardiac hypertrophy. From above results, we suggest for the first time that the alteration of $K_{Ca}$ channels are involved in impaired coronary reserve in isoproterenol-induced cardiac hypertrophy.

• Bulletin of the Korean Chemical Society
• /
• v.11 no.6
• /
• pp.560-563
• /
• 1990

A.c. susceptibility for $Bi_{1.4}Pb_{0.6}Sr_2Ca_2Cu_{3.6}O_x$ superconductor is measured as a function of temperature at different value of a.c. magnetic field amplitude. Two transition steps are attributed to the intergranular and intragranular properties. Based on Bean's critical state model, intergranular critical current density, $J_c^{gb}$ (11 $A/cm^2$ at 77 K) and intragranular critical current density, $J_c^g (7{\times}10^3\;A/cm^2$ at 100 K) are estimated. The low values of $J_c^{gb}$and $J_c^g$ reflect a poor nature of coupling between grains and the low pinning force density of intragrain in $Bi_{1.4}Pb_{0.6}Sr_2Ca_2Cu_{3.6}O_x$ superconductor.