• The Korean Journal of Physiology and Pharmacology
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• v.9 no.2
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• pp.95-101
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• 2005

In the heart, $Na^{+}-Ca^{2+}$ exchange (NCX) is the major $Ca^{2+}$ extrusion mechanism. NCX has been considered as a relaxation mechanism, as it reduces global $[Ca^{2+}]_i$ raised during activation. However, if NCX locates in the close proximity to the ryanodine receptor, then NCX would curtail $Ca^{2+}$ before its diffusion to global $Ca^{2+}_i$ This will result in a global $[Ca^{2+}]_i$ decrease especially during its ascending phase rather than descending phase. Therefore, NCX would decrease the myocardial contractility rather than inducing relaxation in the heart. This possibility was examined in this study by comparing NCX-induced extrusion of $Ca^{2+}$ after its release from SR in the presence and absence of global $Ca^{2+}_i$ transient in the isolated single rat ventricular myocytes by using patch-clamp technique in a whole-cell configuration. Global $Ca^{2+}_i$ transient was controlled by an internal dialysis with different concentrations of BAPTA added in the pipette. During stimulation with a ramp pulse from +100 mV to -100 mV for 200 ms, global $Ca^{2+}_i$ transient was suppressed only mildly, and completely at 1 mmol/L, and 10 mmol/L BAPTA, respectively. In these situations, ryanodine-sensitive inward NCX current was compared using $100{\mu}mol/L$ ryanodine, $Na^+$ depletion, 5 mmol/L $NaCl_2$ and $1{\mu}mol/L$ nifedipine. Surprisingly, the result showed that the ryanodine-sensitive inward NCX current was well preserved after 10 mmol/L BAPTA to 91 % of that obtained after 1 mmol/L BAPTA. From this result, it is concluded that most of the NCX-induced $Ca^{2+}$ extrusion occurs before the $Ca^{2+}$ diffuses to global $Ca^{2+})i$ in the rat ventricular myocyte.

• 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.20 no.6
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• pp.649-655
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• 2016

TonEBP belongs to the Rel family of transcription factors and plays important roles in inflammation as well as kidney homeostasis. Recent studies suggest that TonEBP expression is also involved in differentiation of several cell types such as myocytes, chondrocytes, and osteocytes. In this study, we investigated the roles of TonEBP during adipocyte differentiation in 3T3-L1 cells. TonEBP mRNA and protein expression was dramatically reduced during adipocyte differentiation. Sustained expression of TonEBP using an adenovirus suppressed the formation of lipid droplets as well as the expression of FABP4, a marker of differentiated adipocytes. TonEBP also inhibited the expression of $PPAR{\gamma}$, a known master regulator of adipocytes. RNAi-mediated knock down of TonEBP promoted adipocyte differentiation. However, overexpression of TonEBP did not affect adipogenesis after the initiation of differentiation. Furthermore, TonEBP expression suppressed mitotic clonal expansion and insulin signaling, which are required early for adipocyte differentiation of 3T3-L1 cells. These results suggest that TonEBP may be an important regulatory factor in the early phase of adipocyte differentiation.

• The Korean Journal of Physiology and Pharmacology
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• v.7 no.6
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• pp.333-339
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• 2003

It has been demonstrated that an unidentified cytosolic factor(s) reduces $K_{ACh}$ channel function. Therefore, this study attempted to elucidate the cytosolic factor. Fresh cytosol isolated from normal heart (FC) depressed the $K_{ACh}$ channel activity, but cytosol isolated from the ischemic hearts (IC) did not modulate the channel function. Electrophorectic analysis revealed that a protein of ${\sim}80 kDa was markedly reduced or even lost in IC. By using peptide sequencing analysis and Western blot, this 80 kDa protein was identified as transferrin (receptor-mediated $Fe^{3+}$ transporter, 76 kDa). Direct application of transferrin (100 nM) to the cytoplasmic side of inside-out patches decreased the open probability ($P_o$, 12.7${\pm}6.4%, n=4) without change in mean open time (${\tau}_o$, $98.5{\pm}1.3$%, n=4). However, the equimolar apotransferrin, which is free of $Fe^{3+}$, had no effect on the channel activity (N*$P_o$, $129.1{\pm}13.5$%, n=3). Directly applied $Fe^{3+}$ (100 nM) showed results similar to those of transferrin (N*$P_o$: $21.1{\pm}3.9$%, n=5). However $Fe^{2+}$ failed to reduce the channel function (N*$P_o$, $106.3{\pm}26.8$%, n=5). Interestingly, trivalent cation La3+ inhibited N*$P_o$ of the channel ($6.1{\pm}3.0$%, n=3). Taken together, these results suggest that $Fe^{3+}$ bound to transferrin can modulate the $K_{ACh}$ channel function by its electrical property as a polyvalent cation.

• The Korean Journal of Physiology and Pharmacology
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• v.16 no.5
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• pp.327-332
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• 2012

Sertraline is a commonly used antidepressant of the selective serotonin reuptake inhibitors (SSRIs) class. In these experiments, we have used the whole cell patch clamp technique to examine the effects of sertraline on the major cardiac ion channels expressed in HEK293 cells and the native voltage-gated $Ca^{2+}$ channels in rat ventricular myocytes. According to the results, sertraline is a potent blocker of cardiac $K^+$ channels, such as hERG, $I_{Ks}$ and $I_{K1}$. The rank order of inhibitory potency was hERG > $I_{K1}$ > $I_{Ks}$ with $IC_{50}$ values of 0.7, 10.5, and 15.2 ${\mu}M$, respectively. In addition to $K^+$ channels, sertraline also inhibited $I_{Na}$ and $I_{Ca}$, and the $IC_{50}$ values are 6.1 and 2.6 ${\mu}M$, respectively. Modification of these ion channels by sertraline could induce changes of the cardiac action potential duration and QT interval, and might result in cardiac arrhythmia.

• The Korean Journal of Physiology and Pharmacology
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• v.11 no.2
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• pp.45-55
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• 2007

We elucidated the effects of various components of ischemic medium on the outcome of simulated ischemia-reperfusion injury. Hypoxia for up to 12 hours induced neither apoptotic bodies nor LDH release. However, reoxygenation after 6 or 12 hours of hypoxia resulted in a marked LDH release along with morphological changes compatible with oncotic cell death. H9c2 cells were then subjected to 6 hours of simulated ischemia by exposing them to modified hypoxic glucose-free Krebs-Henseleit buffer. Lowered pH (pH 6.4) of simulated-ischemic buffer resulted in the generation of apoptotic bodies during ischemia, with no concomitant LDH release. The degree of reperfusion-induced LDH release was not affected by the pH of ischemic buffer. Removal of sodium bicarbonate from the simulated ischemic buffer markedly increased cellular damages during both the simulated ischemia and reperfusion. Addition of lactate to the simulated ischemic buffer increased apoptotic cell death during the simulated ischemia. Most importantly, concomitant acidosis and high lactate concentration in ischemic buffer augmented the reperfusion-induced oncotic cell death. These results confirmed the influences of acidosis, bicarbonate deprivation and lactate on the progression and outcome of the simulated ischemia-reperfusion, and also demonstrated that concomitant acidosis and high lactate concentration in simulated ischemic buffer contribute to the development of reperfusion injury.

• 한국생물공학회:학술대회논문집
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• 2005.10a
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• pp.916-916
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• 2005

• 한국생물공학회:학술대회논문집
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• 2005.10a
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• pp.225-225
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• 2005

• BMB Reports
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• v.48 no.9
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• pp.501-506
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• 2015

Based on the potential beneficial effects of growth hormone releasing peptide (GHRP)-6 on muscle functions, a newly synthesized GHRP-6-biotin conjugate was tested on cultured myoblast cells. Increased expression of myogenic marker proteins was observed in GHRP-6-biotin conjugate-treated cells. Additionally, increased expression levels of insulin-like growth factor-1 and collagen type I were observed. Furthermore, GHRP-6-biotin conjugate-treated cells showed increased metabolic activity, as indicated by increased concentrations of energy metabolites, such as ATP and lactate, and increased enzymatic activity of lactate dehydrogenase and creatine kinase. Finally, binding protein analysis suggested few candidate proteins, including desmin, actin, and zinc finger protein 691 as potential targets for GHRP6-biotin conjugate action. These results suggest that the newly synthesized GHRP-6-biotin conjugate has myogenic stimulating activity through, at least in part, by stimulating collagen type I synthesis and several key proteins. Practical applications of the GHRP-6-biotin conjugate could include improving muscle condition. [BMB Reports 2015; 48(9): 501-506]

• Biomolecules & Therapeutics
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• v.1 no.1
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• pp.9-19
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• 1993

DA-125, a new anthracycline antibiotic, showed antitumor activity against animal tumors and human tumors. Therefore we studied the cardiotoxic potential of DA-125 in hamsters and rats as a part of safety research, and compared it with that of doxorubicin(DXR). In acute cardiotoxicity test model used hamsters DA-125 was administered intravenously at a dose of 6, 9, 12 mg/kg, and DXR at 3 mg/kg was given. The electrocardiogram(ECG) of hamsters was recorded for 30 minutes after administration. The DA-125 caused slight ECG alterations at a dose of 6 mg/kg. At a dose of 12 mg/kg DA-125 induced moderate to remarkable changes in ECG like decrease of heart rate, widening of PR interval and 07 interval, and A-V block in 3 out of 5 animals. The severity of ECG alteration at 12 mg/kg of DA-125 was similar to that at 3mg/kg of DXR and these changes caused by DA-125 and DXR recovered within 10 minutes after injection. In chronic cardiotoxicity test model used rats, DA-125 was administered intravenously once a week for three weeks at a dose of 6, 9mg/kg and DXR was given at a dose of 6mg/kg. Electrocardiogram was recorded every week from the start of administration to 2 weeks after the last administration and the animals were sacrificed for histological heart examination at 1 week or 2 weeks after the last administration. DA-125 did not cause any abnormal changes in ECG and in histological heart examination due to administration, but DXR caused widening of ST segment, QRS complex, and QT interval from 1 week after administration and these changes were continued to necropsy. These alterations in ECG were accompanied by cardiac histological lesions such as vacuolation in myocardiac cells, interstitial edema and necrosis of myocytes. These results suggest that DA-125 is less cardiotoxic than DXR.