• The Korean Journal of Physiology and Pharmacology
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• 제3권6호
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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.

• 약학회지
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• 제28권3호
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• pp.129-138
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• 1984

Specific [$^{3}H$] ouabain binding and $Ca^{2+}$ -uptake were measured to elucidate the role of high affinity [$^{3}H$] ouabain binding site in rat cardiac myocytes which contain 65% of rod cells. High affinity [$^{3}$H] ouabain binding site, which is about 3% of total pump sites, with apparent dissociation constant ($K_{D}$) of $1.1{\times}10^{-7}M$ and maximum binding site concentration (Bmax) of 1.2 pmol/mg protein ($1.754{\times}10^{5}cells$) were identified. At the concentration of $10^{-7}M$ to $10^{-4}M$, ouabain produced concentration dependent increase in $Ca^{2+}$-uptake of myocytes. The effect of ouabain on $Ca^{2+}$-uptake was not effected by membrane depolarization (elevated K+ in incubation medium) or verapamil. These results suggest that in rat ventricular myocytes the ouabain receptor complex to high affinity site may increase Na+ - $Ca^{2+}$ exchange across the sarcolemmal membrane by inhibition of Na+, K+ - ATPase.

• Biomolecules & Therapeutics
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• 제24권1호
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• pp.19-24
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• 2016

Acute myocardial infarction (AMI) remains a leading cause of morbidity and mortality worldwide. The exploration of new biomarkers with high sensitivity and specificity for early diagnosis of AMI therefore becomes one of the primary task. In the current study, we aim to detect whether there is any heart specific long noncoding RNA (lncRNA) releasing into the circulation during AMI, and explore its function in the neonatal rat cardiac myocytes injury induced by $H_2O_2$. Our results revealed that the cardiac-specific lncRNA MHRT (Myosin Heavy Chain Associated RNA Transcripts) was significantly elevated in the blood from AMI patients compared with the healthy control ($^*p<0.05$). Using an in vitro neonatal rat cardiac myocytes injury model, we demonstrated that lncRNA MHRT was upregulated in the cardiac myocytes after treatment with hydrogen peroxide ($H_2O_2$) via real-time RT-PCR (qRT-PCR). Furthermore, we knockdowned the MHRT gene by siRNA to confirm its roles in the $H_2O_2$-induced cardiac cell apoptosis, and found that knockdown of MHRT led to significant more apoptotic cells than the non-target control ($^{**}p<0.01$), indicating that the lncRNA MHRT is a protective factor for cardiomyocyte and the plasma concentration of MHRT may serve as a biomarker for myocardial infarction diagnosis in humans AMI.

• The Korean Journal of Physiology and Pharmacology
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• 제3권5호
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• pp.507-512
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• 1999

Contribution of prostaglandins $D_2,\;E_2\;and\;I_2\;(PGD_2,\;PGE_2\;and\;PGI_2)$ on the regulation of ATP-sensitive $K^+$ channel $(K_{ATP}\;channel)$ was investigated in isolated single rat ventricular cardiac myocytes using the patch clamp technique. $PGD_2,\;PGE_2\;and\; PGI_2$ did not affect $K_{ATP}$ channel activity in the inside-out patch, but increased channel activity in a dose-dependent manner when the channel activities were attenuated by the administration of 100 ${\mu}M$ ATP to the internal solution in the inside-out patch. Channel activations by the prostaglandins were abolished by 50 ${\mu}M$ glibenclamide, a $K_{ATP}$ channel blocker. Dose-response curves of relative channel activity against the ATP concentrations of internal solution in the inside-out patch were shifted to the right in the presence of those three prostaglandins. The rank order of the channel stimulatory potencies $(as\;IC_{50}\;for\;ATP)$ calculated from the dose-response curves were $PGI_2\;>\;PGD_2\;>\;PGE_2.$ Conductance of the channel was not changed by those three prostaglandins. In conclusion, we suggest that prostaglandins $D_2,\;E_2\;and\;I_2$ are involved in the regulation of $K_{ATP}$ channel activity in certain circumstances, and that those three prostaglandins may cause myocardial relaxation by opening $K_{ATP}$ channels, thus protecting the heart from ischema.

• 약학회지
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• 제50권2호
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• pp.111-117
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• 2006

Cardiac chambers serve as mechanosensory systems during the haemodynamic or mechanical disturbances. To examine a possible role of fluid pressure (FP) in the regulatien of atrial $Ca^{2+}$ signaling we investigated the effect of FP on L-type $Ca^{2+}$ current $(I_{Ca})$ in rat ventricular myocytes using whole-cell patch-clamp technique. FP $(\sim40cm\;H_2O)$ was applied to whole area of single myocytes with electronically controlled micro-jet system. FP suppressed the magnitude of peak $I_{Ca}$ by $\cong25\%$ at 0 mV without changing voltage dependence of the current-voltage relationship. FP significantly accelerated slow component in inactivation of $I_{Ca}$, but not its fast component. Analysis of steady-state inactivation curve revealed a reduction of the number of $Ca^{2+}$ channels available for activity in the presence of FP. Dialysis of myocytes with high concentration of immobile $Ca^{2+}$ buffer partially attenuated the FP-induced suppression of $I_{Ca}$. In addition, the intracellular $Ca^{2+}$ buttering abolished the FP-induced acceleration of slow component in $I_{Ca}$ inactivation. These results indicate that FP sup-presses $Ca^{2+}$ currents, in part, by increasing cytosolic $Ca^{2+}$ concentration.

• 약학회지
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• 제55권3호
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• pp.247-250
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• 2011

An increase in ventricular pressure can alter cardiac excitation and contraction. Recent report has demonstrated that fluid pressure (FP) suppresses L-type $Ca^{2+}$ current with acceleration of the current inactivation in ventricular myocytes. Since the L-type $Ca^{2+}$ channels known to be regulated by intracellular pH ($pH_i$), this study was designed to explore whether pressurized fluid flow affects pHi in isolated rat ventricular myocytes. A flow of pressurized (~16 dyne/$cm^2$) fluid, identical to that bathing the myocytes, was applied onto single myocytes, and intracellular $H^+$ concentration was monitored using confocal $H^+$ imaging. FP significantly decreased $pH_i$ by $0.07{\pm}0.01$ pH units (n=16, P<0.01). Intracellular acidosis enhances the activity of $Na^+-H^+$ exchanger (NHE). Therefore, we examined if the NHE activity is increased by FP using the NHE inhibitor, HOE642. Although HOE642 did not alter $pH_i$ in control conditions, it decreased $pH_i$ in cells pre-exposed to FP, suggesting enhancement of NHE activity by FP. In addition, FP-induced intracellular acidosis was larger in cells pre-treated with HOE642 than in cells under the control conditions. These results suggest that FP induces intracellular acidosis and that NHE may contribute to extrude $H^+$ during the FP-induced acidosis in rat ventricular myocytes.

• Biomolecules & Therapeutics
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• 제20권4호
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• pp.386-392
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• 2012

The endothelin (ET) signaling pathway controls many physiological processes in myocardium and often becomes upregulated in heart diseases. The aim of the present study was to investigate the effects of ET receptor upregulation on the contractile function of adult ventricular myocytes. Primary cultured adult rat ventricular myocytes were used as a model system of ET receptor overexpression in the heart. Endothelin receptor type A ($ET_A$) or type B ($ET_B$) was overexpressed by Adenoviral infection, and the twitch responses of infected ventricular myocytes were measured after ET-1 stimulation. Overexpression of $ET_A$ exaggerated positive inotropic effect (PIE) and diastolic shortening of ET-1, and induced a new twitch response including twitch broadening. On the contrary, overexpression of $ET_B$ increased PIE of ET-1, but did not affect other two twitch responses. Control myocytes expressing endogenous receptors showed a parallel increase in twitch amplitude and systolic $Ca^{2+}$ in response to ET-1. However, intracellular $Ca^{2+}$ did not change in proportion to the changes in contractility in myocytes overexpressing $ET_A$. Overexpression of $ET_A$ enhanced both systolic and diastolic contractility without parallel changes in $Ca^{2+}$. Differential regulation of this nature indicates that upregulation of $ET_A$ may contribute to diastolic myocardial dysfunction by selectively targeting myofilament proteins that regulate resting cell length, twitch duration and responsiveness to prevailing $Ca^{2+}$.

• 약학회지
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• 제58권4호
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• pp.245-249
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• 2014

Murrayafoline-A (1-methoxy-3-methylcarbazole) is a monomeric carbazole alkaloid found in Murraya euchrestifolia HAYATA and Glycosmis stenocarpa. We have recently shown that murrayafoline-A has positive inotropic effect in isolated rat ventricular myocytes. To know possible mechanisms for the positive inotropic effect of murrayafoline-A we examined the effects of murrayafoline-A on in situ behavior of cardiac $Ca^{2+}$ release units ('$Ca^{2+}$ sparks') and sarcoplasmic reticulum (SR) $Ca^{2+}$ loading using confocal $Ca^{2+}$ imaging method in single rat ventricular myocytes. Murrayafoline-A significantly increased the frequency (events/($10^3{\mu}m^2{\cdot}s$)) of $Ca^{2+}$ sparks in a concentration-dependent manner, with an $EC_{50}$ of $28{\pm}6.4{\mu}M$ and a maximal ~twofold change. The $Ca^{2+}$ content in the SR, measured as caffeine (10 mM)-induced $Ca^{2+}$ transient, was significantly increased by murrayafoline-A (${\approx}$116% and ${\approx}$123% of control at 25 and 100 ${\mu}M$, respectively). In addition, murrayafoline-A significantly increased the fractional $Ca^{2+}$ release, suggesting increase in the efficacy of $Ca^{2+}$ release at given SR $Ca^{2+}$ loading. These results suggest that murrayafoline-A may enhance contractility via increase in $Ca^{2+}$ release from the SR through the ryanodine receptors in ventricular myocytes.

• The Korean Journal of Physiology and Pharmacology
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• 제7권6호
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• pp.341-348
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• 2003

Mechanical stimuli to the cardiac myocytes initiate many biochemical and physiological events. Stretch-activated cation channels have been suggested to mediate these events. In this study, cell-attached and inside-out excised-patch clamp methods were used to identify stretch-activated cation channels in adult rat atrial myocytes. Channel openings were increased in cell-attached configuration when negative pressure was applied to the pipette, and also in inside-out excised patches by negative pressure. The channel was not permeable to $Cl^-$, $Na^+$ and $Cs^+$, but selectively permeable to $K^+$, and the degree of activation was dependent on the magnitude of negative pressure (full activation at ${\sim} -50 mmHg). In symmetrical 140 mM KCl, the slope conductance was $51.2{\pm}3$ pS between the potentials of -80 and 0 mV and $55{\pm}6$ pS between 0 and +80 mV (n=5). Glibenclamide ($100{mu}M$) or ATP (2 mM) failed to block the channel openings, indicating that it is not ATP-sensitive $K^+$ channel. Arachidonic acid ($30{mu}M$), which has been shown to activate a $K^+$ channel cooperatively with membrane stretch, did not affect the channel activity. $GdCl_3$ ($100{mu}M$) also did not alter the activity. These results demonstrate that the mechanical stretch in rat atrial myocytes activates a novel $K^+$-selective cation channel, which is not associated with other $K^+$ channels such as ATP-sensitive and arachidonic acid-activated $K^+$ channel.

• 약학회지
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• 제59권4호
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• pp.158-163
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• 2015

Cardiac myocytes are subjected to fluid shear stress during each contraction and relaxation. Under pathological conditions, such as valve disease, heart failure or hypertension, shear stress in cardiac chamber increases due to high blood volume and pressure. The shear stress induces proarrhythmic longitudinal global $Ca^{2+}$ waves in atrial myocytes. In the present study, we further explored underlying cellular mechanism for the shear stress-induced longitudinal global $Ca^{2+}$ wave in isolated rat atrial myocytes. A shear stress of ${\sim}16dyn/cm^2$ was applied onto entire single myocyte using pressurized fluid puffing. Confocal $Ca^{2+}$ imaging was performed to measure local and global $Ca^{2+}$ signals. Shear stress elicited longitudinally propagating global $Ca^{2+}$ wave (${\sim}80{\mu}m/s$). The occurrence of shear stress-induced atrial $Ca^{2+}$ wave was eliminated by the inhibition of ryanodine receptors (RyRs) or inositol 1,4,5-trisphosphate receptors ($IP_3Rs$). In addition, pretreatment of phospholipase C (PLC) inhibitor U73122, but not its inactive analogue U73343, abolished the generation of longitudinal $Ca^{2+}$ wave under shear stress. Our data suggest that shear-induced longitudinal $Ca^{2+}$ wave may be induced by $Ca^{2+}$-induced $Ca^{2+}$ release through the RyRs which is triggered by $PLC-IP_3R$ signaling in atrial myocytes.