Biphasic effects of haloperidol on sodium currents in guinea pig ventricular myocytes

Aim： To study the effects of haloperidol on sodium currents （INa） in guinea pig ventricular myocytes. Method： Whole-cell patch clamp technique was employed to evaluate the effects of haloperidol on INa in individual ventricular myocytes. Results： Haloperidol （0.1-3 wnol/L） inhibited INa in a concentration-dependent manner with an IC50 of 0.253±0.015 larnol/L. The inhibition rate of haloperidol （0.3 μmol/L） on INa was 22.14%±0.02%, and the maximum conductance was reduced. Haloperidol significantly reduced the midpoints for the activation and inactivation of INa by 2.09 and 4.09 mV, respectively. The time constant of recovery was increased. The increase in time intervals could only recover by 90.14%±1.4% （n=6）; however, haloperidol at 0.03 μmol/L enhanced INa conductance. The midpoints for the activation and inactivation Of INa were shifted by 1.38 and 5.69 mV, respectively, at this concentration of haloperidol. Conclusion： Haloperidol displayed a biphasic effect on INa in guinea pig cardiac myocytes. High concentrations of haloperidol inhibited INa, while lower concentrations of haloperidol shifted the activation and inactivation curve to the left. Full recovery of recovery curve was not achieved after 0.3 μmol/L haloperidol administration, indicating that the drug affects the inactivated state of sodium channels.     

六肽FRCRSFa对大鼠心室肌Na^＋／Ca^＋交换的抑制

AIM: To study the effect of Phe-Arg-Cys-Arg-Ser-Phe-CONH2 (FRCRSFa) on Na+/Ca2+ exchange and its specificity in rat ventricular myocytes. METHODS: Na+/Ca2+ exchange current (INa+/Ca2+) and other currents were measured using whole-cell voltage clamp technique. RESULTS: A concentration-dependent inhibition of hexapeptide FRCRSFa on Na +/Ca2+ exchange was observed in rat ventricular myocytes. IC50 of inward and outward INa+/Ca2+ were 2 and 4 micromol/L, respectively. FRCRSFa 5 micromol/L did not affect L-type Ca2+ current, voltage-gated Na+ current, transient outward K+ current, and inward rectifier K+ current. CONCLUSION: These data indicate that FRCRSFa is an available inhibitor of Na+/Ca2+ exchange with relative selectivity and m ay be valuable for studies of the Na+/Ca2+ exchange in cardiac myocytes.     

双苯氟嗪对豚鼠心室肌细胞膜钠电流的影响(英文)

目的观察双苯氟嗪对豚鼠心室肌细胞膜钠电流的影响。方法用酶解方法分离豚鼠心室肌细胞,全细胞膜片钳技术记录钠电流。结果将细胞钳制在-80mV,给(-80～+50)mV,50ms和步阶10mV的去极化脉冲,记录到的电流被河豚毒素10μmol·L-1完全抑制。在该刺激条件下,该电流最大激活电压在-20mV左右,翻转电压在+30mV左右,提示该电流为钠电流。双苯氟嗪可以浓度依赖性地抑制钠电流。双苯氟嗪对钠电流的抑制作用在冲洗后可部分恢复,表明其对钠通道的抑制作用具有可逆性。双苯氟嗪可使钠电流I-V曲线上移,但对钠电流的电压依赖性特征、最大激活电压和翻转电压无明显影响。在双苯氟嗪40μmol·L-1存在下,最大激活电压下的峰值电流下降约46%;双苯氟嗪可明显使钠电流稳态失活曲线左移,但不影响曲线的斜率因子。双苯氟嗪40μmol·L-1可使钠电流半数失活电压从(-73.0±4.6)mV减少到(-82.8±7.2)mV。但双苯氟嗪对钠电流稳态激活无明显影响,在双苯氟嗪40μmol·L-1存在下,半数激活电压(-33.7±3.6)mV和斜率因子(5.6±2.4)mV与对照组激活电压(-34.9±5.1)mV和斜率因子(6.0±4.8)mV相比无显著性差异。双苯氟嗪可以使钠电流从失活状态下恢复明显减慢,双苯氟嗪40μmo·lL-1可使恢复时间常数延长(79±28)vs(36±11)ms。结论双苯氟嗪可以浓度依赖性、使用依赖性和频率依赖性地抑制心肌钠电流,并且主要作用于钠电流的失活状态。     

海葵毒素anthopleurin—Q对豚鼠心室肌细胞钠电流的作用

目的:研究从海葵(Anthopleura xanthogrammica)提取的毒素anthopleurin-Q(AP-Q)对豚鼠心室肌钠电流(I_(Na))的作用。方法:用酶消化法分离豚鼠单个心室肌细胞,用全细胞膜片箝技术记录心室肌细胞钠电流。结果:AP-Q 3-30nmol/L浓度依赖性地增大I_(Na),EC_(50)、为104nmol/L(95％可信范围:78-130nmol/L)。AP-Q 300nmol/L使I-V曲线左移,使半数激活电压从(-36.3±2.3)mV变为(-43±23)mV(n=6,P<0.01),半数失活电压从(-75±6)mV变为(-59±5)mV(n=6,P<0.01)。AP-Q 300nmol/L使I_(Na)半数恢复时间从(114±36)ms缩短为(17±2)ms(n=6,P<0.01),并明显减慢I_(Na)的快速失活时间常数(τ_f)。结论:AP-Q对I_(Na)有促进作用并减慢其失活过程。     

双苯氟嗪对豚鼠心室肌细胞L-钙电流的影响

目的:观察双苯氟嗪(Dip)对豚鼠心室肌细胞L-型钙电流(I_(Ca-L))的影响。方法:酶解法制备单个心室肌细胞。应用全细胞膜片箝技术记录豚鼠单个心室肌细胞钙电流。结果:在0.3-30μmol/L范围内,Dip可浓度依赖性地降低电压依赖性激活I_(Ca-L)峰值,被Dip 3μmol/L所抑制的I_(Ca-L)在冲洗5min后可得到部份恢复。但Dip对I_(Ca-L)的电压依赖特征,最大激活电压,以及I_(Ca-L)稳态激活无明显影响。在Dip3μmol/L存在下,半数激活电压(V_(0.5))和斜率参数(к)与对照组相比,差异均无显著性。V_(0.5)分别为(-12.8±1.7)mV和(-13.2±2.4)mV,к分别为(7.1±0.4)mV和(7.5±0.5)mV(P>0.05)。Dip3μmol/L可明显使钙电流稳态失活曲线左移,加速钙通道电压依赖性稳态失活。V_(0.5)分别为(-19.7±2.4)mV和(-31±6)mV,к分别为(3.6±0.3)mV和(1.8±0.2)mV(P<0.05).Dip 3μmol/L还使I_(Ca-L)从失活状态下的恢复明显减慢。结论:Dip主要作用于L-型钙通道的失活状态,加速钙通道失活,并使其从失活状态下恢复减慢,从而抑制I_(Ca-L)。     

Analysis of moricizine block of sodium current in isolated guinea-pig atrial myocytes. Atrioventricular difference of moricizine block

The effects of moricizine on Na+ channel currents (INa) were investigated in guinea-pig atrial myocytes and its effects on INa in ventricular myocytes and on cloned hH1 current were compared using the whole-cell, patch-clamp technique. Moricizine induced the tonic block of INa with the apparent dissociation constant (Kd,app) of 6.3 microM at -100 mV and 99.3 microM at -140 mV. Moricizine at 30 microM shifted the h infinity curve to the hyperpolarizing direction by 8.6 +/- 2.4 mV. Moricizine also produced the phasic block of INa, which was enhanced with the increase in the duration of train pulses, and was more prominent with a holding potential (HP) of -100 mV than with an HP of -140 mV. The onset block of INa induced by moricizine during depolarization to -20 mV was continuously increased with increasing the pulse duration, and was enhanced at the less negative HP. The slower component of recovery of the moricizine-induced INa block was relatively slow, with a time constant of 4.2 +/- 2.0 s at -100 mV and 3.0 +/- 1.2 s at -140 mV. Since moricizine induced the tonic block of ventricular INa with Kd,app of 3.1 +/- 0.8 microM at HP = -100 mV and 30.2 +/- 6.8 microM at HP = -140 mV, and cloned hH1 with Kd,app of 3.0 +/- 0.5 microM at HP = -100 mV and 22.0 +/- 3.2 microM at HP = -140 mV, respectively, either ventricular INa or cloned hH1 had significantly higher sensitivity to moricizine than atrial INa. The h infinity curve of ventricular INa was shifted by 10.5 +/- 3.5 mV by 3 microM moricizine and that of hH1 was shifted by 5.0 +/- 2.3 mV by 30 microM moricizine. From the modulated receptor theory, we have estimated the dissociation constants for the resting and inactivated state to be 99.3 and 1.2 microM in atrial myocytes, 30 and 0.17 microM in ventricular myocytes, and 22 and 0.2 microM in cloned hH1, respectively. We conclude that moricizine has a higher affinity for the inactivated Na+ channel than for the resting state channel in atrial myocytes, and moricizine showed the significant atrioventricular difference of moricizine block on INa. Moricizine would exert an antiarrhythmic action on atrial myocytes, as well as on ventricular myocytes, by blocking Na+ channels with a high affinity to the inactivated state and a slow dissociation kinetics.     

Esmolol inhibits Na+ current in rat ventricular myocytes

Esmolol is a unique cardioselective, intravenous, ultra-short acting, beta1-adrenergic blocking agent. It has been widely applied in treating ventricular and supraventricular arrhythmias, especially in emergency situations. In this study the effects of esmolol on sodium current (I(Na)) were investigated by the whole cell patch-clamp recording technique in isolated adult rat ventricular myocytes. The results indicated that esmolol reversibly inhibited I(Na) in a concentration-dependent manner, with an IC50 of 74.2 +/- 0.60 micromol l(-1) with a Hill coefficient of 1.02 +/- 0.04. This inhibition was voltage- and frequency-dependent. Esmolol decreased the peak of the I-V relationship curve at -35 mV from 16.97 +/- 1.68 pA/pF to 6.96 +/- 0.51 pA/pF. The steady-state inactivation curve of I(Na) was shifted to more negative potentials, the voltage at half-inactivation changing from -78.75 +/- 2.3 mV in control to -85.94 +/- 3.2 mV in the presence of esmolol. The development of resting inactivation from closed states was accelerated by esmolol, the time constant was shortened from 62.75 +/- 3.21 ms to 24.93 +/- 2.43 ms, whereas the activation curve was not altered. I(Na) from inactivation could not be recovered completely in the presence of esmolol. These results suggest that esmolol inhibits I(Na) through sodium channel in rat ventricular myocytes by mechanisms involving preferential interaction with the inactivated state and acceleration of the development of inactivation directly from resting state. Therefore, the effect of inhibitory sodium of esmolol may play a vital role in its antiarrhythmic efficacy.     

花生四烯酸对兔心室肌细胞电压门控钠通道的影响

目的研究花生四烯酸(AA)对兔心室肌细胞电压门控钠通道(VGSC)的影响。方法酶解法分离兔心室肌细胞,采用标准全细胞膜片钳技术记录电压门控钠通道电流(INa)。结果AA可浓度依赖性抑制INa,使INa的I-U曲线上移,但其激活电位、电位峰值和反转电位保持不变;AA使INa稳态失活曲线左移,恢复曲线右移;但对INa的抑制作用不具有明显的频率依赖性。结论AA对INa具有浓度依赖性抑制作用,主要是通过抑制失活和失活后恢复过程而发挥作用。因此AA对INa的抑制作用可能是AA抗心律失常,保护心肌的作用机制之一。     

Inhibition of cardiac sodium currents by toluene exposure

Toluene is an industrial solvent widely used as a drug of abuse, which can produce sudden sniffing death due to cardiac arrhythmias. In this paper, we tested the hypothesis that toluene inhibits cardiac sodium channels in Xenopus laevis oocytes transfected with Nav1.5 cDNA and in isolated rat ventricular myocytes. In oocytes, toluene inhibited sodium currents (INa+) in a concentration-dependent manner, with an IC50 of 274 microm (confidence limits: 141-407 microm). The inhibition was complete, voltage-independent, and slowly reversible. Toluene had no effect on: (i). the shape of the I-V curves; (ii). the reversal potential of Na+; and (iii). the steady-state inactivation. The slow recovery time constant from inactivation of INa+ decreased with toluene exposure, while the fast recovery time constant remained unchanged. Block of INa+ by toluene was use- and frequency-dependent. In rat cardiac myocytes, 300 microm toluene inhibited the sodium current (INa+) by 62%; this inhibition was voltage independent. These results suggest that toluene binds to cardiac Na+ channels in the open state and unbinds either when channels move between inactivated states or from an inactivated to a closed state. The use- and frequency-dependent block of INa+ by toluene might be responsible, at least in part, for its arrhythmogenic effect.     

Effect of resveratrol on L-type calcium current in rat ventricular myocytes

AIM: To study the effect of resveratrol on L-type calcium current (I(Ca-L)) in isolated rat ventricular myocytes and the mechanisms underlying these effects. METHODS: I(Ca-L) was examined in isolated single rat ventricular myocytes by using the whole cell patch-clamp recording technique. RESULTS: Resveratrol (10-40 micromol/L) reduced the peak amplitude of I(Ca-L) and shifted the current-voltage (I-V) curve upwards in a concentration-dependent manner. Resveratrol (10, 20, 40 micromol/L) decreased the peak amplitude of I(Ca-L) from -14.2+/-1.5 pA/pF to -10.5+/-1.5 pA/pF (P<0.05), -7.5+/-2.4 pA/pF (P<0.01), and -5.2+/-1.2 pA/pF (P<0.01), respectively. Resveratrol (40 micromol/L) shifted the steady-state activation curve of I(Ca-L) to the right and changed the half-activation potential (V0.5) from -19.4+/-0.4 mV to -15.4+/-1.9 mV (P<0.05). Resveratrol at a concentration of 40 micromol/L did not affect the steady-state inactivation curve of I(Ca-L), but did markedly shift the time-dependent recovery curve of I(Ca-L) to the right, and slow down the recovery of I(Ca-L) from inactivation. Sodium orthovanadate (Na(3)VO(4); 1 mmol/L), a potent inhibitor of tyrosine phosphatase, significantly inhibited the effects of resveratrol (P<0.01). CONCLUSION: Resveratrol inhibited I(Ca-L) mainly by inhibiting the activation of L-type calcium channels and slowing down the recovery of L-type calcium channels from inactivation. This inhibitory effect of resveratrol was mediated by the inhibition of protein tyrosine kinase in rat ventricular myocytes.