• 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.

• Journal of the Korean Ceramic Society
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• v.49 no.2
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• pp.197-203
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• 2012

In this study, in order to improve densification of $La_{0.8}Ca_{0.2}Cr_{0.9}Co_{0.1}O_{3-\delta}$ (LCCC), which is known for one of the most proper candidate interconnector materials in the solid oxide fuel cells, $CaCrO_4$ was prepared via solid oxide synthesis route and added to the LCCC with different amount and particle sizes. As the amount of the $CaCrO_4$ increased, porosity of the sintered samples increased, and the pore size was proportional to the particle size of the $CaCrO_4$. This supports the fact that the $CaCrO_4$ phase forms liquid during sintering and permeate into the matrix leaving behind large pores. Then the liquid reacts with the matrix through the solid solution. However, when the samples were sintered with a slow ramp up rates, the porosity decreased. This is thought to be caused by the progressive solid solution of $CaCrO_4$ before the temperature reach to the melting temperature and forms a fluent amount of liquids. The sintering behavior of the LCCC with the addition of $CaCrO_4$ was analyzed through the transient liquid phase sintering on the basis of the microstructure observation and phase identification by x-ray diffraction.

• Journal of Ginseng Research
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• v.39 no.4
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• pp.398-405
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• 2015

Background: Ginseng has been used as a tonic for invigoration of the human body. In a previous report, we identified a novel candidate responsible for the tonic role of ginseng, designated gintonin. Gintonin induces $[Ca^{2+}]_i$ transient in animal cells via lysophosphatidic acid receptor activation. Gintonin-mediated $[Ca^{2+}]_i$ transient is linked to anti-Alzheimer's activity in transgenic Alzheimer's disease animal model. The previous method for gintonin preparation included multiple steps. The aim of this study is to develop a simple method of gintonin fraction with a high yield. Methods: We developed a brief method to obtain gintonin using ethanol and water. We extracted ginseng with fermentation ethanol and fractionated the extract with water to obtain water-soluble and water-insoluble fractions. The water-insoluble precipitate, rather than the water-soluble supernatant, induced a large $[Ca^{2+}]_i$ transient in primary astrocytes. We designated this fraction as gintonin-enriched fraction (GEF). Results: The yield of GEF was approximately 6-fold higher than that obtained in the previous gintonin preparation method. The apparent molecular weight of GEF, determined using sodium dodecyl sulfate-polyacrylamide gel electrophoresis, was equivalent to that obtained in the previous gintonin preparation method. GEF induced $[Ca^{2+}]_i$ transient in cortical astrocytes. The effective dose (ED50) was $0.3{\pm}0.09{\mu}g/mL$. GEF used the same signal transduction pathway as gintonin during $[Ca^{2+}]_i$ transient induction in mouse cortical astrocytes. Conclusion: Because GEF can be prepared through water precipitation of ginseng ethanol extract and is easily reproducible with high yield, it could be commercially utilized for the development of gintoninderived functional health food and natural medicine.

• 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 and Pharmacology
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• v.3 no.6
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• pp.623-630
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• 1999

Decreased cardiac contractility occurs in endotoxicosis, but little is known about the ionic mechanism responsible for myocardial dysfunction. In this study, we examined the changes in $Ca{2+}$ and $K^+$ currents in cardiac myocytes from endotoxin-treated rat. Ventricular myocytes were isolated from normal and endotoxemic rats (ex vivo), that were treated for 10 hours with Salmonella enteritidis lipopolysaccharides (LPS; 1.5 mg/kg) intravenously. Normal cardiac myocytes were also incubated for 6 hours with 200 ng/ml LPS (in vitro). L-type $Ca{2+}$ current $(I_{Ca,L})$ and transient outward $K^+$ current $(I_{to})$ were measured using whole cell patch clamp techniques. Peak $I_{Ca,L}$ was reduced in endotoxemic myocytes (ex vivo; 6.00.4 pA/pF, P＜0.01) compared to normal myocytes (control; 10.90.6 pA/pF). Exposure to endotoxin in vitro also attenuated $I_{Ca,L}$ (8.40.4 pA/pF, P＜0.01). The amplitude of $(I_{to})$ on depolarization to 60 mV was reduced in endotoxin treated myocytes (16.51.5 pA/pF, P＜0.01, ex vivo; 20.00.9 pA/pF, P＜0.01 , in vitro) compared to normal myocytes (control; 24.71.0 pA/pF). There was no voltage shift in steady-state inactivation of $I_{Ca,L}$ and $(I_{to})$ between groups. These results suggest that endotoxin reduces $Ca{2+}$ and $K^+$ currents of rat cardiac myocytes, which may lead to cardiac dysfunction.

• The Korean Journal of Physiology and Pharmacology
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• v.24 no.4
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• pp.287-298
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• 2020

Ca²⁺ signaling of endothelial cells plays a critical role in controlling blood flow and pressure in small arteries and arterioles. As the impairment of endothelial function is closely associated with cardiovascular diseases (e.g., atherosclerosis, stroke, and hypertension), endothelial Ca²⁺ signaling mechanisms have received substantial attention. Increases in endothelial intracellular Ca²⁺ concentrations promote the synthesis and release of endothelial-derived hyperpolarizing factors (EDHFs, e.g., nitric oxide, prostacyclin, or K⁺ efflux) or directly result in endothelial-dependent hyperpolarization (EDH). These physiological alterations modulate vascular contractility and cause marked vasodilation in resistance arteries. Transient receptor potential (TRP) channels are nonselective cation channels that are present in the endothelium, vascular smooth muscle cells, or perivascular/sensory nerves. TRP channels are activated by diverse stimuli and are considered key biological apparatuses for the Ca²⁺ influx-dependent regulation of vasomotor reactivity in resistance arteries. Ca²⁺-permeable TRP channels, which are primarily found at spatially restricted microdomains in endothelial cells (e.g., myoendothelial projections), have a large unitary or binary conductance and contribute to EDHFs or EDH-induced vasodilation in concert with the activation of intermediate/small conductance Ca²⁺-sensitive K⁺ channels. It is likely that endothelial TRP channel dysfunction is related to the dysregulation of endothelial Ca²⁺ signaling and in turn gives rise to vascular-related diseases such as hypertension. Thus, investigations on the role of Ca²⁺ dynamics via TRP channels in endothelial cells are required to further comprehend how vascular tone or perfusion pressure are regulated in normal and pathophysiological conditions.

• The Korean Journal of Physiology and Pharmacology
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• v.7 no.1
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• pp.25-28
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• 2003

Ion channel inhibitors are widely used for pharmacological discrimination between the different channel types as well as for determination of their functional role. In the present study, we tested the hypothesis that 4-aminopyridine (4-AP) could affect the large conductance $Ca^{2+}$-activated $K^+$ channel ($BK_{Ca}$) currents using perforated-patch or cell-attached configuration of patch-clamp technique in the rabbit pulmonary arterial smooth muscle. Application of 4-AP reversibly inhibited the spontaneous transient outward currents (STOCs). The reversal potential and the sensitivity to charybdotoxin indicated that the STOCs were due to the activation of $BK_{Ca}$. The $BK_{Ca}$ currents were recorded in single channel resolution under the cell-attached mode of patch-clamp technique for minimal perturbation of intracellular environment. Application of 4-AP also inhibited the single $BK_{Ca}$ currents reversibly and dose-dependently. The membrane potential of rabbit pulmonary arterial smooth muscle cells showed spontaneous transient hyperpolarizations (STHPs), presumably due to the STOC activities, which was also inhibited by 4-AP. These results suggest that 4-AP can inhibit $BK_{Ca}$ currentsin the intact rabbit vascular smooth muscle. The use of 4-AP as a selective voltage-dependent $K^+$ (KV) channel blocker in vascular smooth muscle, therefore, must be reevaluated.

• The Korean Journal of Physiology and Pharmacology
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• v.23 no.3
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• pp.219-227
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• 2019

Polycystic kidney disease 2-like-1 (PKD2L1), polycystin-L or transient receptor potential polycystin 3 (TRPP3) is a TRP superfamily member. It is a calcium-permeable non-selective cation channel that regulates intracellular calcium concentration and thereby calcium signaling. Although the calmodulin (CaM) inhibitor, calmidazolium, is an activator of the PKD2L1 channel, the activating mechanism remains unclear. The purpose of this study is to clarify whether CaM takes part in the regulation of the PKD2L1 channel, and if so, how. With patch clamp techniques, we observed the current amplitudes of PKD2L1 significantly reduced when co-expressed with CaM and $CaM{\triangle}N$. This result suggests that the N-lobe of CaM carries a more crucial role in regulating PKD2L1 and guides us into our next question on the different functions of two lobes of CaM. We also identified the predicted CaM binding site, and generated deletion and truncation mutants. The mutants showed significant reduction in currents losing PKD2L1 current-voltage curve, suggesting that the C-terminal region from 590 to 600 is crucial for maintaining the functionality of the PKD2L1 channel. With PKD2L1608Stop mutant showing increased current amplitudes, we further examined the functional importance of EF-hand domain. Along with co-expression of CaM, ${\triangle}EF$-hand mutant also showed significant changes in current amplitudes and potentiation time. Our findings suggest that there is a constitutive inhibition of EF-hand and binding of CaM C-lobe on the channel in low calcium concentration. At higher calcium concentration, calcium ions occupy the N-lobe as well as the EF-hand domain, allowing the two to compete to bind to the channel.

• 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.19 no.2
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• pp.113-125
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• 1985

Electrophysiological difference of the central and peripheral area of the sinoatrial node in the rabbit was studied by glass microelectrode technique. Effects of $K^+,\;Na^+,\;Cs^+,$ adrenaline and ouabain on the action potential of the two areas were investigated, and transient hyperpolarization ($K^+-induced$ hyperpolarization) which developed following readmission of potassium after having pre-treated with $K^+-free$ Tyrode solution for 10 minutes was analyzed. The results obtained were as follows ; 1) The frequency of the spontaneous action potential recorded in the periphery of the SA node was faster than the central area. Reduction by $Cs^+$ and increase by O mM $K^+$, $10^{-6}M$ adrenaline and $10^{-6}M$ ouabain in the frequency of action potential were noticed more prominently in the peripheral than the central area. On the contrary, the frequency in the central area was more decreased than the Peripheral area by 13 mH $K^+$ and 1 mM $Co^{2+}$. 2) The amplitude of the K+_induced hyperpolarization was very small in the central area but large in the peripheral area. Transient hyperpolarization was abolished by ouabain and low sodium, and decreased by cooling the tissue $(17^{\circ}C)$. 3) By changing the concentration of $Ca^{2+}$ in the perfusate, the amplitude and the rate of transient hyperpolarization were increased in the high $Ca^{2+}$ concentration. It could be concluded that the central area of the SA node is less susceptible to the inhibition of Na-Pump and more susceptible to Ca-blocker and high concentration of $K^+$. The Na-Pump activity of the central area measured by means of transient hyperpolarization is found to be much less active than that of the peripheral area.