토끼 심방근에서 Na-Ca 교환 전류에 대한 Bay K, cAMP, Isoprenaline 효과

호원경,엄융의,Ho, Won-Kyung,Earm, Yung-E 대한생리학회 1990 대한생리학회지 Vol.24 No.2

Ca movements during the late plateau phase in rabbit atrium implicate Na-Ca exchange. In single atrial cells isolated from the rabbit the properties of the inward current of Na-Ca exchange were investigated using the whole cell voltage clamp technique. The inward currents were recorded during repolarization following brief 2 ms depolarizing pulse to +40 mV from a holding potential of -70 mV. Followings are the results obtained: 1) When stimulated every 30 sec, the inward currents were activated and reached peak values $6{\sim}12\;ms$ after the beginning of depolarizing pulse. The mean current amplitude was 342 pA/cell. 2) The current decayed spontaneously from the peak activation and the timecourse of the relaxation showed two different phases: fast and slow phase. 3) The recovery of the inward current was tested by paired pulse of various interval. The peak current recovered exponentialy with a time course similar to that of Ca current recovery. 4) Relaxation timecourse was also affected by pulse interval and time constant was reduced almost linearly according to the decrease of pulse interval between 30 sec and 1 sec. 5) The peak inward current was increased by long prepulse stimulation, Bay K, isoprenaline or c-AMP. 6) The relaxation time constant of the inward current was prolonged by Bay K or c-AMP, and shortened by isoprenaline. From the above results, it could be concluded that increase of the calcium current potentiates and prolongs intracellular calcium transients, while shortening of the timecourse by isoprenaline or short interval stimulations might be due to the facilitation of Ca uptake by SR.

단일심근 세포의 활동전압 및 막전류에 대한 Na-Ca 교환기전의 영향

호원경,서인석,엄융의,Ho, Won-Kyung,So, In-Suk,Earm, Yung-E 대한생리학회 1989 대한생리학회지 Vol.23 No.2

The electrophysiological properties of the inward current contributing to the late plateau phase of the action potential were investigated using the whole cell clamp technique and intracellular dialysis in single atrial cells isolated from the rabbit heart. The inward current was activated by various repolarizing pulses after a brief depolarizing pulse to +40 mV for 2 ms and its time course was similar to that of the late plateau of the action potential. The current was fully activated above the potential of -40 mV and abolished by intracellular EGTA. Ryanodine of $1{\mu}M$ also abolished the late plateau and the inward current. Reduced $Na_o\;to\;30%\;and\;20\;mM\;Na_1$ diminished the late plateau together with the inward current. Diltiazem blocked the activation of the current and Ni in the concentration of $40{\sim}200\;{\mu}M$ decreased the development of the late plateau and the inward current. Fully activated current-voltage relation of the inward current showed exponential voltage dependency which was steeper in more hyperplarizing range. The above findings suggest that the inward current was activated by intracellular calcium and contribute the late plateau phase of the action potential. It could be concluded that the inward current would be the inward component of Na-Ca exchange.

동방결절 전기적 특성에 대한 $Ca^{2+}$ 효과의 온도에 따른 변화

호원경,김기환,황상익,Ho, Won-Kyung,Kim, Ki-Whan,Hwang, Sang-Ik 대한생리학회 1987 대한생리학회지 Vol.21 No.1

There is evidence that the effect of extracellular $Ca^{2+}$ on heart rate is temperature-dependent: at $38^{\circ}C$ excess $Ca^{2+}$ induces positive chronotropic response, whereas at $30^{\circ}C$ there is no significant chronotropic effect of $Ca^{2+}$. The cause of this temperature-dependency, however, remains still unclear. Therefore, this study was undertaken to investigate the chronotropic effect of external $Ca^{2+}$ at different temperature in the isolated rabbit atria and in the small strips of SA node cut perpendicularly to crista terminalis. In the isolated atria, the $Ca^{2+}$ effect was temperature-dependent: at $35^{\circ}C$ excess $Ca^{2+}$ evoked positive chronotropic response, while at $30^{\circ}C$ there was no significant changes in sinus rate. On the contrary, in the small SA strips external $Ca^{2+}$ induced negative chronotropic effect. At $35^{\circ}C$ changes in $Ca^{2+}$ concentration from 2 to 4, 6, and 10 mM decreased the sinus rate by $2.7{\pm}1.6%$, $11.2{\pm}3.7%$ and $23.2{\pm}8.1%$ respectively. Lowering the temperature to $30^{\circ}C$, the negative chronotropic effect of $Ca^{2+}$ became greater. With intracellular microelectrodes transmembrane potential was recorded in the small SA strips at $30^{\circ}C$, $35^{\circ}C$ and $38^{\circ}C$. As temperature increased from 30 to $38^{\circ}C$, sinus rate was accelerated by $13/min/^{\circ}C$, $APD_{50}$(action ptential duration from peak to 50% repolarization) decreased by $5\;msec/^{\circ}C$, and amplitude of action potential was slightly decreased. With an increase in $Ca^{2+}$ concentrations from 0.5 to 6 mM, overshoot increased and MDP decreased. These $Ca^{2+}$ effects on the overshoot and MDP of action potentials were not altered by temperature. But the $Ca^{2+}$ effects on the rates of diastolic depolarization, systolic depolarization and repolarization were modified by temperature. Discrpancy of the chronotropic effects of $Ca^{2+}$ between isolated atria and small SA strips was discussed.

동방결절 전기적 특성에 대한 Ca²⁺ 효과의 온도에 따른 변화

호원경(Ho, Won-Kyung),김기환(Kim, Ki-Whan),황상익(Hwang, Sang-Ik) 대한생리학회 1987 대한생리학회지 Vol.21 No.1

There is evidence that the effect of extracellular Ca²⁺ on heart rate is temperature-dependent: at 38℃ excess Ca²⁺ induces positive chronotropic response, whereas at 30℃ there is no significant chronotropic effect of Ca²⁺. The cause of this temperature-dependency, however, remains still unclear. Therefore, this study was undertaken to investigate the chronotropic effect of external Ca²⁺ at different temperature in the isolated rabbit atria and in the small strips of SA node cut perpendicularly to crista terminalis. In the isolated atria, the Ca²⁺ effect was temperature-dependent: at 35℃ excess Ca²⁺ evoked positive chronotropic response, while at 30℃ there was no significant changes in sinus rate. On the contrary, in the small SA strips external Ca²⁺ induced negative chronotropic effect. At 35℃ changes in Ca²⁺ concentration from 2 to 4, 6, and 10 mM decreased the sinus rate by 2.7±1.6%, 11.2±3.7% and 23.2±8.1% respectively. Lowering the temperature to 30℃, the negative chronotropic effect of Ca²⁺ became greater. With intracellular microelectrodes transmembrane potential was recorded in the small SA strips at 30℃, 35℃ and 38℃. As temperature increased from 30 to 38℃, sinus rate was accelerated by 13/min/℃, APD₅₀(action ptential duration from peak to 50% repolarization) decreased by 5 msec/℃, and amplitude of action potential was slightly decreased. With an increase in Ca²⁺ concentrations from 0.5 to 6 mM, overshoot increased and MDP decreased. These Ca²⁺ effects on the overshoot and MDP of action potentials were not altered by temperature. But the Ca²⁺ effects on the rates of diastolic depolarization, systolic depolarization and repolarization were modified by temperature. Discrpancy of the chronotropic effects of Ca²⁺ between isolated atria and small SA strips was discussed.

토끼에서 태자를 통하지 않은 양수내 $Li^{+}$의 이동

김영제,호원경,성호경,Kim, Young-Jae,Ho, Won-Kyung,Sung, Ho-Kyung 대한생리학회 1990 대한생리학회지 Vol.24 No.1

The extrafetal transfer of $Li^{+}$ in amniotic fluid was studied in 45 pregnant rabbits. LiCl solution was administered either intravenously to mother or directly into the amniotic sac and monitored the appearance and disappearance of $Li^{+}$ in the amniotic fluid, then calculated the transfer rate of $Li^{+}$ of extrafetal origin. To study the transplacental $Li^{+}$ transfer, a solution of 150 mM LiCl was infused continuously via maternal vein (initial dose: 0.7 mmol/kg, maintaining dose: 0.03 mmol/kg/min) and the $Li^{+}$ concentration was measured in maternal blood and amniotic fluid after 60 and 120 minutes of infusion. Change in the volume of aminotic fluid was determined by Congo red dilution method at the same time. Effects of duration of gestation was not considered in this study. Extrafetal transport of $Li^{+}$ into the amniotic fluid was estimated by comparing the $Li^{+}$ concentration and volume of amniotic fluid determined before and after ligating the placental vessels. Extrafetal $Li^{+}$ transport from the amniotic fluid was determined by observing the time dependent disappearance of $Li^{+}$ and Congo red in amniotic fluid after injecting 0.5 ml solution of 15 mM or 90 mM LiCl and 50 mg/ml Congo red. Following are the results obtained: 1) During infusion of LiCl through maternal vein the ratio of the aminotic $Li^{+}$/maternal plasma $Li^{+}$ increased significantly along with the increment of fetal weight. 2) The volume of amniotic fluid of larger fetuses than 20.5 gm increased significantly during administration of LiCl while that of smaller fetuses did not change. 3) After umbilical cord ligation the $Li^{+}$ concentration of amniotic fluid of larger fetuses than 20.5 gm was decreased to $59.9{\pm}10.3%$ and $56.9{\pm}42.9%$ $(mean{\pm}S.D.)$ of those of control group after 60 and 120 minutes of LiCl infusion respectively. In amniotic fluid of smaller fetuses than 20.5 gm, there was no significant difference between control and ligation groups. 4) The disappearance rate of Congo red in the amniotic fluid was $45.2{\pm}8.2%/hr$. 5) The disappearance rate of $Li^{+}$ after intraamniotic injection of LiCl depended on the amount injected. On injecting $7.5\;{\mu}mol$ LiCl, $Li^{+}$ disappeared rapidly from the amniotic fluid and the rates after 60 min and 90 min were $97.0{\pm}2.8,\;98.5{\pm}2.0%$ respectively. On injecting $45\;{\mu}mol$ LiCl, the rates were $56.0{\pm}15.4,\;78.9{\pm}14.5%$ at 60 and 90 min. 6) From the above results it was concluded: a) $Li^{+}$ transfer into the amniotic fluid increased along with the fetal growth and one half of $Li^{+}$ influx is through the extrafetal route even after the maturation of fetal kidney. b) One half of the $Li^{+}$ transfer from the amniotic fluid was through swallowing of fetus, while the remaining half was transfered rapidly through amniotic membrane, which was concentration limited.

동방결절에서 과분극에 의해 활성화되는 내향전류에 대한 Cyclic-GMP의 영향

유신,호원경,엄융의,Yoo, Shin,Ho, Won-Kyung,Earm, Yung-E 대한약리학회 1997 The Korean Journal of Physiology & Pharmacology Vol.1 No.6

The aim of present study is to investigate the effects of cGMP on hyperpolarization activated inward current ($I_f$), pacemaker current of the heart, in rabbit sino-atrial node cells using the whole-cell patch clamp technique. When sodium nitroprusside (SNP, $80{\mu}M$), which is known to activate guanylyl cyclase, was added, $I_f$ amplitude was increased and its activation was accelerated. However, when $I_f$ was prestimulated by isopreterenol (ISO, $1{\mu}M$), SNP reversed the effect of ISO. In the absence of ISO, SNP shifted activation curve rightward. On the contrary in the presence of ISO, SNP shifted activation curve in opposite direction. $8Br-cGMP(100\;{\mu}M)$, more potent PKG activator and worse PDE activator than cGMP, also increased basal $I_f$ but did not reverse stimulatory effect of ISO. It was probable that PKG activation seemed to be involved in SNP-induced basal $I_f$ increase. The fact that SNP inhibited ISO-stimulated $I_f$ suggested cGMP antagonize cAMP action via the activation of PDE. This possibility was supported by experiment using 3-isobutyl-1-methylxanthine (IBMX), non-specific PDE inhibitor. SNP did not affect $I_f$ when $I_f$ was stimulated by $20{\mu}M$ IBMX. Therefore, cGMP reversed the stimulatory effect of cAMP via cAMP breakdown by activating cGMP-stimulated PDE. These results suggest that PKG and PDE are involved in the modulation of $I_f$ by cGMP: PKG may facilitate $I_f$ and cGMP-stimulated PDE can counteract the stimulatory action of cAMP.

토끼 단일 심방근 세포에서 Na-Ca 교환전류의 특성에 관한 연구

염욱,호원경,서경필,Youm, Wook,Ho, Won-Kyung,Suh, Kyung-Phill 대한흉부심장혈관외과학회 1989 Journal of Chest Surgery (J Chest Surg) Vol.22 No.4

In single atrial cells isolated from the rabbit the properties of inward current of Na-Ca exchange were investigated using the whole cell voltage clamp technique. The current was recorded during repolarization following brief 2 ms depolarizing pulse to +40 mV from a holding potential of * 70 mV. Followings are the results obtained: 1. When stimulated every 30 seconds, the inward currents were activated and reached peak values 6-12 ms after the beginning of depolarizing pulse. The mean current amplitude was 342 pA/cell. 2. The current decayed spontaneously from the peak activation and the time course of the relaxation showed two different phases fast and slow phase. The time constants were 10-18 ms and 60-140 ms, respectively. 3. The recovery of inward current was tested by paired pulse of various intervals. The peak current recovered exponentially with time constant of 140 ms and 1 p M isoprenaline accelerated the recovery process. 4. Relaxation time course was also affected by pulse interval and time constant of the fast phase was reduced almost linearly according to the decrease of pulse interval between 30 sec and 1 sec. 5. The peak activation was increased in magnitude by long prepulse stimulation, 5 p M Bay K, 1 p M isoprenaline or internal and external application of c-AMP. 6. The relaxation time constant of the fast phase was prolonged by 5 p M Bay K or c-AMP, and shortened by isoprenaline. However the time course of the slow relaxation phase was not so much changed. From the above results, it could be concluded that increase of the calcium current by Bay K or c-AMP results in the potentiation and prolongation of intracellular calcium transient, and the facilitation of Ca uptake by SR might be a mechanism of shortening the time constant of current relaxation by short interval stimulation or isoprenaline.

토끼 단일 심근세포에서 대사억제시 Inward Rectifier$(I_{K1})$의 변화

정유정,호원경,엄융의,Chung, Yu-Jeong,Ho, Won-Kyung,Earm, Yung-E 대한약리학회 1997 The Korean Journal of Physiology & Pharmacology Vol.1 No.6

In the present study, we have investigated the effect of metabolic inhibition on the inward rectifier K current ($I_{K1}$). Using whole cell patch clamp technique we applied voltage ramp from +80 mV to -140 mV at a holding potential of -30 mV and recorded the whole cell current in single ventricular myocytes isolated from the rabbit heart. The current-voltage relationship showed N-shape (a large inward current and little outward current with a negative slope) which is a characteristic of $I_{K1}$. Application of 0.2 mM dinitrophenol (DNP, an uncoupler of oxidative phosphorylation as a tool for chemical hypoxia) to the bathing solution with the pipette solution containing 5 mM ATP, produced a gradual increase of outward current followed by a gradual decrease of inward current with little change in the reversal potential (-80 mV). The increase of outward current was reversed by glibenclamide ($10\;{\mu}M$), suggesting that it is caused by the activation of $K_{ATP}$. When DNP and glibenclamide were applied at the same time or glibenclamide was pretreated, DNP produced same degree of reduction in the magnitude of the inward current. These results show that metabolic inhibition induces not only the increase of $K_{ATP}$ channel but also the decrease of $I_{K1}$. Perfusing the cell with ATP-free pipette solution induced the changes very similar to those observed using DNP. Long exposure of DNP (30 min) or ATP-free pipette solution produced a marked decrease of both inward and outward current with a significant change in the reversal potential. Above results suggest that the decrease of $I_{K1}$ may contribute to the depolarisation of membrane potential during metabolic inhibition.

고양이 척수전근 감각신경섬유의 흥분전도속도

김전,황상익,호원경,Kim, Jun,Hwang, Sang-Ik,Ho, Won-Kyung 대한생리학회 1987 대한생리학회지 Vol.21 No.1

This study was aimed to investigate whether the conduction velocity of nerve impulses through the ventral afferent fibers is constant along their entire courses in dorsal as well as in ventral roots. Cats were anesthetized with ${\alpha}-chloralose$ (60 mg/kg, i.p.) and artificially ventilated. Laminectomies were done on L4-S1 spinal vertebrae to expose the lumbosacral spiral cord. Both ventral and dorsal roots of L7 or S1 spinal segments were isolated and cut near the spinal cord. Ventral roots were placed on 6-lead stimulating electrodes and stimulated with supra C-threshold intensity. Divided dorsal root fascicles were placed on bipolar recording electrodes and single fiber units activated by the stimulation of the ventral roots were identified. Followings are the results obtained: 1) A total of 27 VRA units were identified. 10 units of them conducted impulses slower than 2 m/sec. Conduction velocities of the remaining units were in the range of 3.11-20.91 m/sec. 2) In 12 Units conduction velocities Of the VRA units through dorsal$(CV_{DR})$ and venral root$(CV_{DR})$ were determined respectively. There was a tendency to conduct impulses faster through dorsal roots$(CV_{DR}=8.19{\pm}3.26\;m/sec)$ than ventral roots$(CV_{DR}=3.46{\pm}1.02\;m/sec)$. From the above results we confirmed that there exist nerve fibers in continuity between the spinal ventral and dorsal roots but we could not ascertain whether there is a change in conduction velocity through the entire course of ventral afferent unit.

동방결절 활동전압에 대한 아데노신 효과

김기환(Kim, Ki-Whan),호원경(Ho, Won-Kyung) 대한생리학회 1984 대한생리학회지 Vol.18 No.1

Since the first report of Drury and Szent-GyÖrgyi in 1929, the inhibitory influences of adenosine on the heart have repeatedly been described by many investigators. These studies have shown that adenosine and adenine nucleotides have overall depressant effects, similar to those of acetylcholine. Heart beats become slow and weak. It is also well known that adenosine is a potent endogenous coronary vasodilator. Many investigations on the working mechanisms of adenosine have been focused mainly on the effects of the coronary blood flow. However, the cellular mechanisms underlying the inhibitory action of adenosine on sinus node are not well understood yet. Thus, this study was undertaken to examine the behavior of rabbit SA node under influence of adenosine. In these series of experiments three kinds of preparations were used: whole atrial pair, left atrial strip, and isolated SA node preparations. The electrical activity of SA node was recorded with conventional glass microelectrodes 30 to 50 MΩ. The preparations were superfused with bicarbonate-buffered Tyrode solution of pH 7.35 and aerated with a gas mixture of 3% CO₂-97% O₂ at 35℃. In whole atrial pair, adenosine suppressed sinoatrial rhythm in a dose-dependent manner. Effect of adenosine on atrial rate appeared at the concentration of 10^-5M and was enhanced in parallel with the increase in adenosine concentration. Inhibitory action of adenosine on pacemaker activity was more prominent in the preparation pretreated with norepinephrine, which can steepen the slope of pacemaker potential by increasing permeability of Ca⁺². Calcium ions in perfusate slowly produced a marked change in sinoatrial rhythm. Elevation of the calcium concentration from 0.3 to 8 mM increased the atrial rate from 132 to 174 beats/min, but over 10 mM Ca⁺² decreased. The inhibitory effect of adenosine on sinoatrial rhythm developed very rapidly. Atrial rate was recovered promptly from the adenosine-induced suppression by the addition of norepinephrine, but extra Ca⁺² was less suitable to restore the suppression of atrial rate. Adenosine suppressed also atrial contractility in the same dosage range that restricted pacemaker activity, even in the reserpinized preparation. In isolated SA node preparation, spontaneous firing rate of SA node at 35℃(mean±SEM, n=16) was 154±3.3 beats/min. The parameters of action potentials were: maximum diastolic potential(MDP), -73±1.7 mV: overshoot(OS), 9±1.4 mV: slope of pacemaker potential(SPP), $94±3.0 mV/sec. Adenosine suppressed the firing rate of SA node in a dose-dependent manner. This inhibitory effect appeared at the concentration of 10^-6M and was in parallel with the increase in adenosine concentration. Changes in action potential by adenosine were dose-dependent increase of MDP and decrease of SPP until 10^-4M. Above this concentration, however, the amplitude of action potential decreased markedly due to the simultaneous decrease of both MDP and OS. All these effects of adenosine were not affected by pretreatment of atropine and propranolol. Lowering extra Ca²⁺ irom 2 mM to 0.3 mM resulted in a marked decrease of OS and SPP, but almost no change of MDP. However, increase of perfusate Ca²⁺ from 2 mM to 6 or 8 mM produced a prominent decrease of MDP and a slight increase of OS and SPP. Dipyridamole(DPM), which is known to block the adenosine transport across the cell membrane, definately potentiated the action of adenosine. The results of this experiment suggest that adenosine suppressed pacemaker activity and atrial contractility simultaneously and directly, by decreasing Ca²⁺-permeability of nodal and atrial cell membranes.