未成年人心房肌细胞瞬间外向钾电流和内向整流钾电流的特性

AIM: To study the properties of transient outward K+ current (Ito) and inward rectifier K+ current (IKl) in immature human heart. METHODS: Ito and IKl were recorded using whole-cell patch-clamp technique in atrial myocytes isolated from 12 immature (aged from 6 months to 5 a) human hearts. RESULTS: Ito was voltage-dependent, activated and inactivated rapidly. The IC50 (95% confidence limits) of 4-AP on Ito was 0.64 (0.48-0.87) mmol.L-1. 4-AP 1 mmol.L-1 shifted V1/2 of activation from (6.6 +/- 2.0) mV to (19.8 +/- 3.0) mV (n = 4-10, P < 0.01). 4-AP 0.3 mmol.L-1 changed V1/2 of inactivation from (-49 +/- 4) mV to (-61.4 +/- 2.1) mV (n = 3, P < 0.01), but there were no obvious influence on voltage-dependent activation of Ito (P > 0.05). At the same concentration, the recovery time constant (tau value) was prolonged from (108 +/- 16) ms to (220 +/- 67) ms (n = 3-12, P < 0.01). IKl was also voltage-dependent. Its reverse potential was -40 mV. CONCLUSION: Both Ito and IKl are important K+ channel currents in immature human atrial myocytes. 4-AP can affect the inactivation and recovery of Ito at low concentration (0.3 mmol.L-1) and affect its activation at high concentration (1 mmol.L-1).     

雌激素对Kv2.1钾电流及大鼠海马神经元延迟整流钾电流的影响

目的研究17β-雌二醇对Kv2.1钾电流和原代培养大鼠海马神经元延迟整流钾电流的作用。方法采用HEK293-Kv2.1细胞培养、大鼠海马神经元原代培养和膜片钳全细胞记录技术。结果17β-雌二醇浓度依赖地抑制Kv2.1钾电流和原代培养大鼠海马神经元延迟整流钾电流(I_K)。17β-雌二醇抑制Kv2.1钾电流和原代培养大鼠海马神经元延迟整流钾电流的IC₅₀分别为2.4和4.0 μmol·L^-1。通道动力学研究发现，17β-雌二醇(3 μmol·L^-1)显著左移Kv2.1钾电流的稳态激活和失活曲线，但只显著左移海马神经元延迟整流钾电流稳态激活曲线，而不影响该电流的稳态失活曲线。结论17β-雌二醇抑制Kv2.1钾电流与抑制I_K的程度相近，17β-雌二醇抑制I_K的作用可能部分通过阻断Kv2.1钾电流而实现。     

硫酸镁对大鼠海马神经元瞬间外向钾电流和延迟整流钾电流的抑制作用

目的研究硫酸镁(MgSO₄)对大鼠海马神经元瞬间外向钾电流(I_A)和延迟整流钾电流(I_K)的作用。方法 全细胞膜片钳技术。结果MgSO₄可浓度依赖地抑制I_A和I_K,半数抑制浓度IC₅₀分别为6.30和7.60 mmol·L^-1;此外还与电压呈依赖性关系,但不具有频率依赖性。6 mmol·L^-1 MgSO₄非常显著地影响I_A和I_K的激活过程,但不改变二者的斜率因子。另外6 mmol·L^-1 MgSO₄还非常显著地影响I_A的失活过程,但不改变其斜率因子。结论 MgSO₄抑制大鼠海马神经元的I_A和I_K,并改变I_A和I_K的激活过程和失活过程。这可能是其抗缺血缺氧引发的中枢神经系统损伤,具有神经保护作用的机制之一。     

低渗膨胀增加豚鼠胃窦环行肌细胞钙激活钾电流和延迟整流型钾电流

目的:观察低渗膨胀对豚鼠胃窦环行肌细胞钙激活钾电流和延迟整流型钾电流的影响。方法:采用传统全细胞膜片箱技术,对以胶原酶急性分离的单细胞进行低渗灌流,观察钾电流的变化。结果:低渗 灌流液(200 Osmmol/kg)可增加钙激活钾电流和延迟整流型钾电流,钙激活钾电流的增加可被四乙基胺4mmol·L~(-1)和Charybdotoxin 200nmol·L~(-1)完全抑制;延迟整流型钾电流的增加可被四乙基胺4mmol·L~(-1)部分抑制,可被4-氨基吡啶10mmol·L~(-1)完全抑制。两种钾电流的增加幅度无显著性差异(P>0.05)。钙激活钾电流在施加低渗灌流(17.0±4.8)s后增加;延迟整流型钾电流在(30.7±13.7)s后增加,两者的潜伏期存在显著性差异(P<0.05)。结论:低渗膨胀可增加钙激活钾电流和延迟整流型钾电流,这种增加效应可能与细胞容积调节有关。     

未成年人心房肌细胞瞬间外向钾电流和内向整流钾电流的特性(英文)

目的:研究未成年人心房肌细胞瞬间外向钾电流(I_(to))和内向整流钾电流(I_(Kl))的特性。方法:膜片箝全细胞技术。结果:I_(to)是电压依赖性电流,快速激活,快速失活,被I_(to)的选择性阻断剂4-AP阻断。IC_(50)=0.64mmol·L~(-1)。4-AP1mmol·L~(-1)使I_(to)的半数激活电位增加;4-AP0.3mmol·L~(-1)使I_(to)的半数失活电位减少,对激活曲线没有明显影响并使I_(to)的恢复时间延长。I_(Kl)也表现出电压依赖的特性,其反转电位在-40mV。结论:在未成年人心房肌细胞上,I_(to)和I_(Kl)是两种重要的K~ 通道电流。4-AP0.3mmol·L~(-1)时对I_(to)的失活和失活后的恢复有明显影响,1mmol·L~(-1)时影响I_(to)的激活。     

阿米洛利对豚鼠心肌细胞钾电流及钙电流的作用

目的研究阿米洛利（amiloride）对豚鼠心肌细胞钾电流及钙电流的作用。方法采用全细胞膜片钳技术记录豚鼠心室肌细胞钾通道及钙通道电流。结果阿米洛利在10~100 μmol·L^-1抑制L型及T型钙电流,不改变钙电流I-V曲线的形状，仅抑制这两型电流的幅度。当累积浓度达100 μmol·L^-1时，阿米洛利轻微抑制快激活延迟整流钾电流(I_Kr)，对慢激活延迟整流钾电流(I_Ks)无影响。阿米洛利在1~100 μmol·L^-1浓度依赖性地抑制内向整流钾电流(I_K1)。结论阿米洛利抑制电压依赖性的钾、钙电流，为其抗心律失常作用提供了离子基础。     

他克林对培养大鼠海马神经元延迟整流钾电流和瞬间外向钾电流的影响

目的研究他克林对培养大鼠海马神经元上延迟整流钾电流(I_K)和瞬间外向钾电流(I_A)的影响。方法 大鼠海马神经元原代培养,全细胞膜片钳记录培养大鼠海马神经元上电压依赖性外向钾电流和瞬间外向钾电流变化。结果他克林明显抑制海马神经元延迟整流钾电流和瞬间外向钾电流,呈浓度依赖性,对延迟整流钾电流的敏感性高于瞬间外向钾电流。30 μmol·L^-1他克林显著影响I_K和I_A稳态激活曲线,使所有电流的V_1/2左移。结论他克林明显抑制延迟整流钾电流和瞬间外向钾电流,对延迟整流钾电流的敏感性高于瞬间外向钾电流。     

充血性心衰病人心房肌细胞瞬间外向钾电流和超快延迟整流钾电流的特征

目的:研究充血性心衰病人心房肌细胞瞬间外向钾电流(I_(to))和超快延迟整流钾电流(I_(Kur))的特征.方法:全细胞膜片箝技术.结果:心衰病人心房肌细胞上的I_(to)的激活和失活具有电压依赖性及时间依赖性.其半数最大激活电位(V_(1/2))和半数最大失活电位(V_(1/2))分别为(15±12)mV和(-45±4)mV.当膜电位从-40mV升至 60mV时,激活时间常数均值从(6.9±2.3)ms降至(1.40±0.20)ms,失活时间常数均值从(69±17)ms降至(21±14)ms,两者均随着膜电位的增加而减小.此外,该通道从失活状态下的恢复也很快.当保持电位为-80mV时,其恢复时间常数为(125±65)ms,但在此条件下通道的恢复不完全.当测试脉冲频率为0.2-2 Hz时,此通道电流未表现出明显的频率依赖性.与I_(to)相比,I_(Kur)的激活只具有电压依赖性但无时间依赖性.当测试电位为 60mV时,其电流密度平均为(3.4±0.7)pA/pF.半数最大激活电位(V_(1/2))为(23±14)mV.在测试脉冲频率为0.2-2Hz的范围内,通道电流也无明显的频率依赖性.结论:I_(to)和I_(Kur)是充血性心衰病人心房肌细胞上主要的外向电流,其大小和动力学特征可显著地影响心房肌细胞的电生理特性.     

辣椒素对培养的大鼠三叉神经节神经元瞬时外向钾电流和延迟整流钾电流的影响

目的探讨辣椒素(capsaicin)对大鼠三叉神经节神经元瞬时外向钾电流(I_A)和延迟整流钾电流(I_K)的不同影响。方法采用全细胞膜片钳方法。结果对于辣椒素敏感神经元，辣椒素可选择性、剂量依赖性地抑制其I_A电流，但辣椒素对I_K无明显选择性作用；对于辣椒素不敏感神经元，辣椒素对I_A和I_K均无作用，且对I_A和_IK激活动力学亦无影响。结论辣椒素可选择性抑制对其敏感的三叉神经节神经元I_A，这可能是初次应用辣椒素时其致痛作用的原因之一。     

妥卡尼对豚鼠心室肌细胞钙电流和钾电流的抑制作用

利用酶分散的成年豚鼠心室肌细胞和全细胞电压钳技术,研究了妥卡尼(tocainide)对心室肌细胞钙电流(I_ca)、延迟整流钾电流(I_k)和ATP敏感性钾电流(Ik,ATP)的作用。结果表明,妥卡尼对I_ca和I_k均显示浓度相关的抑制作用,妥卡尼50umol·L^-1对I_ca和I_k的抑制率分别为16%和3%。这可能是妥卡尼有效抑制室上性心动过速和缩短心肌动作电位平台期的重要机制。     

Effects of U50,488H on transient outward and ultra-rapid delayed rectifier K+ currents in young human atrial myocytes

The effects of trans-(+/-)-3,4-dichloro-N-methyl-N-[2-(1-pyrrolidinyl)-cyclohexyl]-benzeneacetamide methanesulfonate salt (U50,488H), a selective kappa-opioid receptor agonist, on transient outward K+ current (Ito1) and ultra-rapid delayed rectifier K+ current (IKur) in young human atrial myocytes were evaluated with a whole-cell patch-clamp technique. At +10 mV, U50,488H decreased Ito1 in a concentration-dependent manner (IC50=12.4+/-3.5 microM), while at +50 mV, U50,488H produced biphasic effects on Ito1-increasing and decreasing the current at 1-3 and 10-30 microM, respectively. U50,488H at 10 microM shifted the midpoint (V0.5) of Ito1 activation in a depolarizing direction by approximately 5 mV, accelerated the inactivation, and slowed the recovery from inactivation of Ito1. In addition, U50,488H inhibited IKur in a concentration-dependent manner (IC50=3.3+/-0.6 microM). The effects of U50,488H on the two types of K+ currents were not antagonized by either 5 microM nor-binaltorphimine or 300 nM naloxone. These results indicate that U50,488H affects both Ito1 and IKur in young human atrial myocytes in an opioid receptor-independent manner.     

The sulphonylurea glibenclamide inhibits voltage dependent potassium currents in human atrial and ventricular myocytes

1 It was the aim of our study to investigate the effects of the sulphonylurea glibenclamide on voltage dependent potassium currents in human atrial myocytes. 2 The drug blocked a fraction of the quasi steady state current (ramp response) which was activated positive to -20 mV, was sensitive to 4-aminopyridine (500 microM) and was different from the ATP dependent potassium current IK(ATP). 3 Glibenclamide dose dependently inhibited both, the peak as well as the late current elicited by step depolarization positive to -20 mV. The IC50 for reduction in charge area of total outward current was 76 microM. 4 The double-exponential inactivation time-course of the total outward current was accelerated in the presence of glibenclamide with a tau(fast) of 12.7+/-1.5 ms and a tau(slow) of 213+/-25 ms in control and 5.8+/-1.9 ms (P<0.001) and 101+/-20 ms (P<0.05) under glibenclamide (100 microM). 5 Our data suggest, that both repolarizing currents in human atrial myocytes, the transient outward current (Ito1) and the ultrarapid delayed rectifier current (IKur) were inhibited by glibenclamide. 6 In human ventricular myocytes glibenclamide inhibited Ito1 without affecting the late current. 7 Our data suggest that glibenclamide inhibits human voltage dependent cardiac potassium currents at concentrations above 10 microM.     

Raloxifene inhibits transient outward and ultra-rapid delayed rectifier potassium currents in human atrial myocytes

The selective estrogen receptor modulator raloxifene is widely used in the treatment of postmenopausal osteoporosis, and has cardioprotective properties. However, effects of raloxifene on cardiac ion channels are unclear. The present study was designed to investigate the effects of raloxifene and beta-estradiol on transient outward and ultra-rapid delayed rectifier potassium currents (Ito1 and IKur) in human atrial myocytes with a whole cell patch-clamp technique. Ito1 was inhibited by raloxifene in a concentration-dependent manner with an IC50 of 0.9 microM. Raloxifene at 1 microM decreased Ito1 by 40.2+/-1.9% (at +50 mV, n=14, P<0.01 vs control). Time-dependent recovery from inactivation was slowed, and time to peak and time-dependent inactivation of Ito1 were significantly accelerated, while steady-state voltage dependent activation and inactivation of Ito1 were not affected by raloxifene. In addition, raloxifene remarkably suppressed IKur (IC50=0.7 microM). Raloxifene at 1 microM decreased IKur by 57.3+/-3.3% (at +50 mV, n=10, P<0.01 vs control). However, beta-estradiol inhibited Ito1 (IC50=10.3 microM) without affecting IKur. The inhibitory effects of raloxifene and beta-estradiol on Ito1 and/or IKur were unaffected by the estrogen receptor antagonist ICI 182,780. Our results indicate that raloxifene directly inhibits the human atrial repolarization potassium currents Ito1 and IKur. Whether raloxifene is beneficial for supraventricular arrhythmias remains to be studied.     

人心房肌细胞瞬间外向钾电流的特性

目的：研究人的心房肌细胞瞬间外向钾电流（Ｉｔｏ）的特性。方法：采用膜片箝全细胞记录法观察人心房肌通道电流的变化，在用ＣｄＣｌ２ ０．１ｍｍｏｌ·Ｌ＾－１心房肌通道电流的变化，在用ＣｄＣｌ２ ０．１ｍｍｏｌ·Ｌ＾－１阻断钙电流的情况下，细胞膜去极化引出瞬间外向钾电流（Ｉｔｏ）。结果：Ｉｔｏ为电压依赖的电流，迅速激活，迅速失活，４－ＡＰ（４－氨基吡啶）１０ｍｍｏｌ·Ｌ＾－１（选择性的Ｉｔｏ的阻断剂）能     

Actions of the anti-oestrogen agent clomiphene on outward K+ currents in rat ventricular myocytes

1. The effects of clomiphene (CLM) on cardiac outward K+ current components from rat isolated ventricular myocytes were investigated using the whole-cell patch-clamp technique. Clomiphene (10 micromol/L) significantly inhibited both peak (Ipeak) and end-pulse (Ilate) outward currents (elicited by a 500 msec voltage step from -40 to +50 mV in the presence of K+-containing intracellular and extracellular solutions) by approximately 37% (n = 6; P < 0.01) and 49% (n = 6; P < 0.01), respectively. In contrast, CLM had no effect on outward currents when K+-free solutions were used. 2. A double-pulse protocol and Boltzmann fitting were used to separate individual K+ current components on the basis of their voltage-dependent inactivation properties. At potentials positive to -80 mV, two inactivating transient outward components (Ito) and (IKx) and a non-inactivating steady state component (Iss) could be distinguished. 3. Clomiphene inhibited both Ito and Iss. The maximal block of Ito and Iss induced by CLM (100 micromol/L) was approximately 61% (n = 5) and 43% (n = 5) with IC50 values of 1.54 +/- 0.39 and 2.2 +/- 0.4 micromol/L, respectively. In contrast, the peak magnitude of IKx was unaltered by CLM, although its time-course of inactivation was accelerated. 4. Further experiments whereby myocytes were superfused with the vasoactive peptide endothelin (ET)-1 (20 nmol/L) revealed that CLM (10 micro mol/L) completely abolished the ET-1-sensitive component of Iss. 5. Our findings demonstrate, for the first time, the effects of CLM on distinct cardiac K+ current components and show that CLM modulates the voltage-gated K+ current components Ito and IKx and inhibits the steady state outward current Iss in rat ventricular myocytes.     

Dibenzylamine--a novel blocker of the voltage-dependent K+ current in myocardial mouse cells

Ventricular myocytes of the mouse ventricle were voltage clamped with a patch-clamp technique in the whole-cell configuration. At depolarizing voltage pulses, these myocytes develop a large voltage-dependent K+ outward current. Application of the drug dibenzylamine (DBA) to the bath solution blocked the voltage-dependent K+ current. The concentration/response relationship for the peak current at +40 mV indicates a 1:1 binding of the drug to the receptor with a concentration of half maximum effect of 43.1 micromol/l. The block did not require activation of the channels by depolarizing pulses. At concentrations causing partial block (25 micromol/l), the block was independent of voltage. At the same concentration, DBA completely blocked the slow component of the recovery from inactivation (-80 mV) whereas steady-state inactivation was not altered. It is concluded that DBA is a novel blocker of the voltage-dependent K+ current in mouse cardiac myocytes which preferentially affects the current component generating the slow recovery from inactivation.     

RP58866对哺乳动物心室肌细胞跨膜钾电流的作用

AIM: To determine effects of RP58866 on inward rectifier K+ current (IKl), transient outward K+ current (Ito) and delayed outward rectifier K+ current (IK) in isolated cardiac myocytes. METHODS: In isolated ventricular myocytes of guinea pig and dog, the effect of RP58866 on IKl, Ito, and IK were observed by the whole cell voltage-clamp technique. RESULTS: RP58866 decreased IKl in a concentration-dependent manner, with an IC50 of (3.4 +/- 0.8) micromol.L-1 (n = 6) at -100 mV in guinea pig ventricular cells. In dog ventricular myocytes, RP58866 inhibited Ito with IC50 of (2.3 +/- 0.5) micromol.L-1 at +40 mV. In guinea pig ventricular cells, RP58866 at 100 micromol.L-1 decreased IK: IKstep by (58 +/- 13)% at +40 mV, and IKtail by (86 +/- 17)%, respectively. RP58866 inhibited IKstep with an IC50 of (7.5 +/- 0.8) micromol.L-1, and IKtail with an IC50 of (3.5 +/- 0.9) micromol.L-1. The envelope of tail analysis suggested that both IKr and IKs were inhibited. CONCLUSION: RP58866 inhibits IKl, Ito, and IK in cardiac myocytes with a similar potency, and is not a specific IKl inhibitor.     

Effect of ketamine on transient outward potassium current of isolated human atrial myocytes

The effects of ketamine on transient outward potassium current (I(to)) of isolated human atrial myocytes were investigated to understand the mechanism of part of its effects by whole-cell patch-clamp. Atrial myocytes were enzymatically isolated from specimens of human atrial appendage obtained from patients under going cardiac valve displacing. Ito is recorded in voltage-clamp modes using the patch-clamp technique at room temperature. Currents signals were recorded by an Axopatch 200B amplifier with the Digidata 1322A-pClamp 9.0 data acquisition system. Ketamine decreased I(to) of human atrial myocytes in a dose-dependent manner. The current-voltage curve was significantly lowered, 30, 100, 300, and 1000 micromol x L(-1) ketamine decreased respectively I(to) current density about (13.62 +/- 0.04)%, (38.92 +/- 0.05)%, (72.24 +/- 0.10)% and (83.84 +/- 0.05)% at the potential of 50 mV, with an IC50 of 121 micromol x L(-1). The I(to) activation curve, inactivation curve and the recovery curve were not altered by ketamine. So, ketamine concentration-dependently decreased I(to) of human atrial myocytes.     

Effects of the antifungal antibiotic clotrimazole on human cardiac repolarization potassium currents

The antifungal antibiotic clotrimazole (CLT) shows therapeutic effects on cancer, sickle cell disease, malaria, etc. by inhibiting membrane intermediate-conductance Ca2+ -activated K+ channels (IKCa). However, it is unclear whether this drug would affect human cardiac K+ currents. The present study was therefore designed to investigate the effects of CLT on transient outward K+ current (Ito1), and ultra-rapid delayed rectifier K+ current (IKur) in isolated human atrial myocytes, and cloned hERG channel current (IhERG) and recombinant human cardiac KCNQ1/KCNE1 channel current (IKs) expressed in HEK 293 cells. It was found that CLT inhibited Ito1 with an IC50 of 29.5 microM, accelerated Ito1 inactivation, and decreased recovery of Ito1 from inactivation. In addition, CLT inhibited human atrial I(Kur) in a concentration-dependent manner (IC50 = 7.6 microM). CLT substantially suppressed IhERG (IC50 = 3.6 microM), and negatively shifted the activation conductance of IhERG. Moreover, CLT inhibited IKs (IC50 = 15.1 microM), and positively shifted the activation conductance of the current. These results indicate that the antifungal antibiotic CLT substantially inhibits human cardiac repolarization K+ currents including Ito1, IKur, IhERG, and IKs. However, caution is recommended when correlating the observed in vitro effects on cardiac ion currents to the clinical relevance.