To determine the effects of HOE 694, a new and potent Na＋- H＋ exchanger blocker, on transient inward current (Iti) and Na＋- Ca2＋ exchange during hypoxia- reoxygenation in guinea pig cardiomyocytes. Methods. Cardio...To determine the effects of HOE 694, a new and potent Na＋- H＋ exchanger blocker, on transient inward current (Iti) and Na＋- Ca2＋ exchange during hypoxia- reoxygenation in guinea pig cardiomyocytes. Methods. Cardiomyocytes were isolated from adult guinea pig ventricle. Experiment was performed in an experimental chamber that allowed the cells to be exposed to a sufficiently low O2 pressure. The cells were subjected to hypoxia and reoxygenation. The ionic currents were studied with patch clamp technique. Results. In the absence of HOE 694, hypoxia- reoxygenation induced Iti in 12 of 15 experiments; but in cardiomyocytes pretreated with HOE 694 (10～ 50μ mol/L), the incidence of Iti observed during reoxygenation was reduced to 5 of 11 experiments and 3 of 10 experiments, P Conclusions. Blockade of the Na＋- H＋ exchange by HOE 694 could reduce Ca2＋ overload upon hypoxia- reoxygenation, and inhibition of Na＋- H＋ exchange may also indirectly decrease Na＋- Ca2＋ exchange activity during hypoxia.展开更多
The Na^+/Ca^(2+) exchanger(NCX) protein family is a part of the cation/Ca^(2+) exchanger superfamily and participates in the regulation of cellular Ca^(2+) homeostasis. NCX1, the most important subtype in the NCX fami...The Na^+/Ca^(2+) exchanger(NCX) protein family is a part of the cation/Ca^(2+) exchanger superfamily and participates in the regulation of cellular Ca^(2+) homeostasis. NCX1, the most important subtype in the NCX family, is expressed widely in various organs and tissues in mammals and plays an especially important role in the physiological and pathological processes of nerves and the cardiovascular system. In the past few years, the function of NCX1 in the digestive system has received increasing attention; NCX1 not only participates in the healing process of gastric ulcer and gastric mucosal injury but also mediates the development of digestive cancer, acute pancreatitis, and intestinal absorption.This review aims to explore the roles of NCX1 in digestive system physiology and pathophysiology in order to guide clinical treatments.展开更多
Objective Background and Objects: Naturally occurring temporal variability of action potentialduration (APD) in isolated myocytes has been noted. Most of the studies have beenfocusing on analyzes of the differences in...Objective Background and Objects: Naturally occurring temporal variability of action potentialduration (APD) in isolated myocytes has been noted. Most of the studies have beenfocusing on analyzes of the differences in ionic channels and currents among theepicardial-, mid-myocardial-(M) and endocardial myocytes, and the rate-dependent (adaptation) characteristics of APD. We have found that the change in APD during achange in frequency of stimulation mostly reflects a change in rate of repolarization at distinct membrane potential levels. We assumed that in the myocytes, there is balancing mechanism, which is constantly adjusting the various ionic currents accommodating to the changing conditions. This intrinsic ability of adaptation is important and may offer some of the consequences of the transmural heterogeneity in adaptation of APD. This adaptive behaviors maybe equally important in maintaining the normal electrophysiological properties and in induction of arrhythmia in a case of error in normal adaptation. Though most studies of Na +/Ca 2+ exchange (NCX) has been emphasized on its reverse activaty during pathyological condition. Our hypothesis is that reverse activaty of NCX also plays an important role in adjusting the repolarization of AP during a physiological condition. A mismatch between action potential (AP) repolarization and relaxation of the contraction can be caused by intracellular Ca 2+ transport abnormalities. Ca 2+ influx via reverse activation of NCX can load the sarcoplasmic recticulum (SR), which has arrhythmogenic effect.Methods We studied the single myocytes from the left ventricle of adult mongrel dogs. During the cell separation, collagenase was perfused through LAD by Langandorff system. We use the patch-clamp system to determinded AP in current clamp mode. Myocyte contraction was imaged by a video camera, shortening of unloaded myocytes was detected by a video edge motion detector, using changes in light intensity at the edges of the myocyte. Results From 60 consecutive recorded APs at a constant 1.0 Hz stimulation under steady state conditions we found there is a variance in the repolarization between 10mV and-40mV. We also found the variance in the APD during the rate adaptation range of repolarization. Fluctuation in the transient may contribute to the APD variability. To test thishypothesis we block the transient by intracellular dialysis with 10 mM EGTA(n=19), this caused a significant reduction in the coefficient variability (CV=SD/mean APD%) from 2.3± 0.8 to 1.3± 0.3 P< 0.01. During a rate change of the stimulation from 0.6 Hz to 1.0 Hz. The AP duration increased from 278±8 msec to 320±9 msec, Mean+SD, n=5, 50 APs, P< 0.05. contraction is accompanied by an after-contraction(A-CON). The relaxation of contraction precedes the repolarization of the AP. We assumed that the enhancement of repolarization and the production of after-contraction can be possibly induced by reverse mode of NCX. Reducing [Na +] o by substitution of 40mM Na + with Li + favors NCX activating the reverse mode, which significantly decreased the dome of the AP from 4.8± 0.3 to -10.6± 1.2mV, P< 0.05, and increased the APD from 330±13 to 368±14 msec. P< 0.05.Conclusions Intracellular calcium transient most likely contributes to the beat-to-beat variance of action potential duration in canine ventricular myocyte. And it attributes to the voltage-dependent switch of NCX mode. Calcium concentration is high inmyocytes during the repolarization, and high intracellular Ca 2+ activates NCX in such a manner, that it generates an inward (positive, depolarizing) current. This current works against the repolarization, it is prolonging it, with other words it increases the duration of the action potential. The magnitude of calcium concentration during repolarization is very much dependent on calcium transport in the SR. The calcium transport in the SR is subject to adrenergic actions, and other physiologic and pathologic regulators. Under pathologic conditions展开更多
We determined whether La3+ enter human peripheral blood lymphocytes via Na+/Ca2+ exchanger (measured with fura-2). We first compared the sensitivity of fura-2 with La3+ and Ca2+, the result indicates that the sensitiv...We determined whether La3+ enter human peripheral blood lymphocytes via Na+/Ca2+ exchanger (measured with fura-2). We first compared the sensitivity of fura-2 with La3+ and Ca2+, the result indicates that the sensitivity of fura-2 for La3+ is much greater than for Ca2+. La3+ forms a 1:1 La3+-fura-2 complex (apparent dissociation constant = 1.7x10(-12) mol/L, pH 7.05). Ouabain-pretreated cells, suspended in Na+-free medium, showed that La3+ can enter human lymphocytes via the Na-i(+)/Ca2+ (La3+)(o) exchanger and is found to be about 10(-12) mol/L in cells exposed to 0.4 mmol/L La3+. Otherwise, the higher concentration (0.1 mmol/L) blocks the Na-i(+)/Ca2+(La3+)(o) exchange-mediated influx of Ca2+, but the lower concentration (0.01 mmol/L) appears to increase Ca2+ entry.展开更多
目的:利用荧光标记法观察代谢抑制处理后,大鼠心肌细胞反向Na+/Ca2+交换体(NCX)转运功能的变化。方法:酶解法分离制备钙耐受心肌细胞用Fura-2/AM负载,采用双激发荧光光电倍增系统(IonOptix Photom etry Sys-tem)检测钙信号。结果:细胞...目的:利用荧光标记法观察代谢抑制处理后,大鼠心肌细胞反向Na+/Ca2+交换体(NCX)转运功能的变化。方法:酶解法分离制备钙耐受心肌细胞用Fura-2/AM负载,采用双激发荧光光电倍增系统(IonOptix Photom etry Sys-tem)检测钙信号。结果:细胞置于无Na+液后,可见[Ca2+]i逐渐升高,L-型Ca2+通道阻断剂n ifed ip ine在浓度为1μmol/L时,不影响此现象;而NCX的抑制剂N i2+,在浓度为1 mmol/L时,则完全阻断[Ca2+]i的升高。采用20mmol/L乳酸加10 mmol/L脱氧葡萄糖作为代谢抑制物处理心肌细胞不同时间,正常Tyrode液灌流10 m in,之后检测无Na+液引发[Ca2+]i升高效应的变化,发现5 m in处理与对照组无显著性差异,10和30 m in处理后此效应逐渐减弱。结论:首次发现,代谢抑制处理后心肌NCX的反向转运功能被抑制,阐明其调节机制,将为心肌缺血/再灌注损伤的治疗提供新思路。展开更多
基金This work was supported by Leading Specialty Funding of Shanghai, Grant No.94- III- 001.
文摘To determine the effects of HOE 694, a new and potent Na＋- H＋ exchanger blocker, on transient inward current (Iti) and Na＋- Ca2＋ exchange during hypoxia- reoxygenation in guinea pig cardiomyocytes. Methods. Cardiomyocytes were isolated from adult guinea pig ventricle. Experiment was performed in an experimental chamber that allowed the cells to be exposed to a sufficiently low O2 pressure. The cells were subjected to hypoxia and reoxygenation. The ionic currents were studied with patch clamp technique. Results. In the absence of HOE 694, hypoxia- reoxygenation induced Iti in 12 of 15 experiments; but in cardiomyocytes pretreated with HOE 694 (10～ 50μ mol/L), the incidence of Iti observed during reoxygenation was reduced to 5 of 11 experiments and 3 of 10 experiments, P Conclusions. Blockade of the Na＋- H＋ exchange by HOE 694 could reduce Ca2＋ overload upon hypoxia- reoxygenation, and inhibition of Na＋- H＋ exchange may also indirectly decrease Na＋- Ca2＋ exchange activity during hypoxia.
基金Supported by the National Natural Science Foundation of China,No.816660412 to Xie R and No.81160265 to Xu JY
文摘The Na^+/Ca^(2+) exchanger(NCX) protein family is a part of the cation/Ca^(2+) exchanger superfamily and participates in the regulation of cellular Ca^(2+) homeostasis. NCX1, the most important subtype in the NCX family, is expressed widely in various organs and tissues in mammals and plays an especially important role in the physiological and pathological processes of nerves and the cardiovascular system. In the past few years, the function of NCX1 in the digestive system has received increasing attention; NCX1 not only participates in the healing process of gastric ulcer and gastric mucosal injury but also mediates the development of digestive cancer, acute pancreatitis, and intestinal absorption.This review aims to explore the roles of NCX1 in digestive system physiology and pathophysiology in order to guide clinical treatments.
文摘Objective Background and Objects: Naturally occurring temporal variability of action potentialduration (APD) in isolated myocytes has been noted. Most of the studies have beenfocusing on analyzes of the differences in ionic channels and currents among theepicardial-, mid-myocardial-(M) and endocardial myocytes, and the rate-dependent (adaptation) characteristics of APD. We have found that the change in APD during achange in frequency of stimulation mostly reflects a change in rate of repolarization at distinct membrane potential levels. We assumed that in the myocytes, there is balancing mechanism, which is constantly adjusting the various ionic currents accommodating to the changing conditions. This intrinsic ability of adaptation is important and may offer some of the consequences of the transmural heterogeneity in adaptation of APD. This adaptive behaviors maybe equally important in maintaining the normal electrophysiological properties and in induction of arrhythmia in a case of error in normal adaptation. Though most studies of Na +/Ca 2+ exchange (NCX) has been emphasized on its reverse activaty during pathyological condition. Our hypothesis is that reverse activaty of NCX also plays an important role in adjusting the repolarization of AP during a physiological condition. A mismatch between action potential (AP) repolarization and relaxation of the contraction can be caused by intracellular Ca 2+ transport abnormalities. Ca 2+ influx via reverse activation of NCX can load the sarcoplasmic recticulum (SR), which has arrhythmogenic effect.Methods We studied the single myocytes from the left ventricle of adult mongrel dogs. During the cell separation, collagenase was perfused through LAD by Langandorff system. We use the patch-clamp system to determinded AP in current clamp mode. Myocyte contraction was imaged by a video camera, shortening of unloaded myocytes was detected by a video edge motion detector, using changes in light intensity at the edges of the myocyte. Results From 60 consecutive recorded APs at a constant 1.0 Hz stimulation under steady state conditions we found there is a variance in the repolarization between 10mV and-40mV. We also found the variance in the APD during the rate adaptation range of repolarization. Fluctuation in the transient may contribute to the APD variability. To test thishypothesis we block the transient by intracellular dialysis with 10 mM EGTA(n=19), this caused a significant reduction in the coefficient variability (CV=SD/mean APD%) from 2.3± 0.8 to 1.3± 0.3 P< 0.01. During a rate change of the stimulation from 0.6 Hz to 1.0 Hz. The AP duration increased from 278±8 msec to 320±9 msec, Mean+SD, n=5, 50 APs, P< 0.05. contraction is accompanied by an after-contraction(A-CON). The relaxation of contraction precedes the repolarization of the AP. We assumed that the enhancement of repolarization and the production of after-contraction can be possibly induced by reverse mode of NCX. Reducing [Na +] o by substitution of 40mM Na + with Li + favors NCX activating the reverse mode, which significantly decreased the dome of the AP from 4.8± 0.3 to -10.6± 1.2mV, P< 0.05, and increased the APD from 330±13 to 368±14 msec. P< 0.05.Conclusions Intracellular calcium transient most likely contributes to the beat-to-beat variance of action potential duration in canine ventricular myocyte. And it attributes to the voltage-dependent switch of NCX mode. Calcium concentration is high inmyocytes during the repolarization, and high intracellular Ca 2+ activates NCX in such a manner, that it generates an inward (positive, depolarizing) current. This current works against the repolarization, it is prolonging it, with other words it increases the duration of the action potential. The magnitude of calcium concentration during repolarization is very much dependent on calcium transport in the SR. The calcium transport in the SR is subject to adrenergic actions, and other physiologic and pathologic regulators. Under pathologic conditions
基金The authors acknowledge the support of the National Natural Scicnce Foundation of ChinaProvincial Natural Science Foundation of Shanxi.
文摘We determined whether La3+ enter human peripheral blood lymphocytes via Na+/Ca2+ exchanger (measured with fura-2). We first compared the sensitivity of fura-2 with La3+ and Ca2+, the result indicates that the sensitivity of fura-2 for La3+ is much greater than for Ca2+. La3+ forms a 1:1 La3+-fura-2 complex (apparent dissociation constant = 1.7x10(-12) mol/L, pH 7.05). Ouabain-pretreated cells, suspended in Na+-free medium, showed that La3+ can enter human lymphocytes via the Na-i(+)/Ca2+ (La3+)(o) exchanger and is found to be about 10(-12) mol/L in cells exposed to 0.4 mmol/L La3+. Otherwise, the higher concentration (0.1 mmol/L) blocks the Na-i(+)/Ca2+(La3+)(o) exchange-mediated influx of Ca2+, but the lower concentration (0.01 mmol/L) appears to increase Ca2+ entry.
文摘目的:利用荧光标记法观察代谢抑制处理后,大鼠心肌细胞反向Na+/Ca2+交换体(NCX)转运功能的变化。方法:酶解法分离制备钙耐受心肌细胞用Fura-2/AM负载,采用双激发荧光光电倍增系统(IonOptix Photom etry Sys-tem)检测钙信号。结果:细胞置于无Na+液后,可见[Ca2+]i逐渐升高,L-型Ca2+通道阻断剂n ifed ip ine在浓度为1μmol/L时,不影响此现象;而NCX的抑制剂N i2+,在浓度为1 mmol/L时,则完全阻断[Ca2+]i的升高。采用20mmol/L乳酸加10 mmol/L脱氧葡萄糖作为代谢抑制物处理心肌细胞不同时间,正常Tyrode液灌流10 m in,之后检测无Na+液引发[Ca2+]i升高效应的变化,发现5 m in处理与对照组无显著性差异,10和30 m in处理后此效应逐渐减弱。结论:首次发现,代谢抑制处理后心肌NCX的反向转运功能被抑制,阐明其调节机制,将为心肌缺血/再灌注损伤的治疗提供新思路。
