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.     

肿瘤坏死因子α对大鼠心室肌细胞钙转运的影响

AIM: To study the effects of tumor necrosis factor-alpha (TNF-alpha) on calcium movement in rat ventricular myocytes. METHODS: Intracellular free Ca2+ concentration was measured with calcium fluorescent probe Fluo-3/AM and laser confocal microscope. L-type calcium current (ICa,L) was recorded with the whole-cell configuration of the patch-clamp techniques. RESULTS: At 2, 20 and 200 microg/L, TNF-alpha was found to increase intracellular free Ca2+ concentration in a dose-dependent manner illustrated by the increment of calcium fluorescence density with laser confocal microscope. Nicardipine 0.5 micromol/L slightly attenuated TNF-alpha-induced response. When the cardiac myocytes were exposed to caffeine (100 mmol/L) for 30 min, TNF-alpha failed to induce any change of intracellular free calcium. However, it was found that TNF-alpha inhibited I(Ca,L) in whole-cell patch-clamp experiments. At 2, 20, and 200 microg/L, TNF-alpha decreased peak I(Ca,L) by 3.9 % (-5.1 pA/pF+/-0.3 pA/pF vs -4.9 pA/pF+/-0.2 pA/pF, n=9, P>0.05), 15.7 % (-5.1 pA/pF+/-0.3 pA/pF vs -4.3 pA/pF+/-0.3 pA/pF, n=9, P<0.05) and 19.6 % (-5.1 pA/pF+/-0.3 pA/pF vs -4.1 pA/pF+/-0.4 pA/pF, n=9, P<0.01), respectively. It shifted the steady-state inactivation curve of I(Ca,L) to the left (V1/2 shifted from -28.7 mV+/-0.3 mV to -37.8 mV+/-1.4 mV, n=7, P<0.05), while it took no effects on steady-state activation and recovery from inactivation. CONCLUSION: TNF-alpha inhibited I(Ca,L) in rat ventricular myocytes, while increasing the intercellular free Ca2+ level due to the release of Ca2+ from intracellular stores.     

5—羟色胺增强去甲肾上腺素诱导的肥厚心肌L—型钙电流

目的:研究5-羟色胺(5-HT)对去甲肾上腺素(NE)诱导的大鼠肥厚心肌L-型钙电流(I_(Ca))的影响.方法:大鼠腹腔注射NE建立心肌肥厚模型;酶解分离单个心室肌细胞;全细胞膜片箝记录I_(Ca).结果:(1)腹腔注射NE第15天,大鼠左心室与体重比增加31.8％(2)肥厚心肌细胞I_(Ca)与正常心肌细胞相比,明显增加0mV时分别为4.5pA/pF±0.5pA/pF和3.5pA/pF±0.3pA/pF(P<0.01).(3)5-HT可显著增加肥厚和正常心肌细胞I_(Ca),并使最大激活电流从0mV降低至-10mV;此外,5-HT增加I_(Ca)作用在肥厚心肌细胞更为显著.(4)稳态激活和失活实验发现,5-HT对稳态激活曲线无显著影响,而影响稳态失活曲线,使半失活电压从-39.5mV±1.8mV升高至-27.8mV±1.7mV(P<0.05),而不改变钙通道电压依赖性(斜率因子k无显著变化).结论:5-HT通过改变L-型钙通道稳态失活特征而显著增加I_(Ca),此作用在肥厚心肌细胞更显著,提示在肥厚心肌5-HT更易于诱导心律失常发生.     

葛根素抑制大鼠心室肌细胞的钠电流

AIM: To study the effect of puerarin (Pue) on Na+ channel in rat ventricular myocytes. METHODS: Whole-cell patch-clamp technique was applied on isolated cardiomyocytes from rats. RESULTS: Pue inhibited cardiac INa in a positive rate-dependent and dose-dependent manner, with an IC(50) of 349 micromol/L. The kinetics of blockage of cardiac sodium channel by Pue resembled the ClassIa/Ic of antiarrhythmic agents. Pue 300 micromol/L did not alter the shape of the I-V curve of INa, but markedly shifted the steady-state inactivation curve of INa towards more negative potential by 15.9 mV, and postponed the recovery of INa inactivation state from (21.9+/-1.6) ms to (54.4+/-3.4) ms (P<0.01). It demonstrated that the steady state of inactivation was affected by Pue significantly. CONCLUSION: Pue protected ventricular myocytes against cardiac damage and arrhythmias by inhibiting recovery from inactivation of cardiac Na+ channels.     

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.     

Effect of the antifibrillatory compound tedisamil (KC-8857) on transmembrane currents in mammalian ventricular myocytes

The cellular mechanism of action of tedisamil (KC-8857) (TED), a novel antiarrhythmic/antifibrillatory compound, was studied on transmembrane currents in guinea pig, rabbit and dog ventricular myocytes by applying the patch-clamp and the conventional microelectrode technique. In guinea pig myocytes the rapid component of the delayed rectifier potassium current (IKr) was largely diminished by 1 microM TED (from 0.88+/-0.17 to 0.23+/-0.07 pA/pF, n=5, p<0.05), while its slow component (IKs) was reduced only by 5 microM TED (from 8.1+/-0.3 to 4.23+/-0.07 pA/pF, n=5, p<0.05). TED did not significantly change the IKr and IKs kinetics. In rabbit myocytes 1 microM TED decreased the amplitude of the transient outward current (I(to)) from 20.3+/-4.9 to 13.9+/-2.8 pA/pF (n=5, p<0.05), accelerated its fast inactivation time constant from 8.3+/-0.6 to 3.5+/-0.5 ms (n=5, p<0.05) and reduced the ATP-activated potassium current (IKATP) from 38.2+/-11.8 to 18.4+/-4.7 pA/pF (activator: 50 microM cromakalim; n=5, p<0.05). In dog myocytes 2 microM TED blocked the fast sodium current (INa) with rapid onset and moderately slow offset kinetics, while the inward rectifier potassium (IK1), the inward calcium (ICa) and even the I(to) currents were not affected by TED in concentration as high as 10 microM. The differences in I(to) responsiveness between dog and rabbit are probably due to the different alpha-subunits of I(to) in these species. It is concluded that inhibition of several transmembrane currents, including IKr, IKs, I(to), IKATP and even INa, can contribute to the high antiarrhythmic/antifibrillatory potency of TED, underlying predominant Class III combined with I A/B type antiarrhythmic characteristics.     

Class III anti-arrhythmia drug E-4031 potentiates Na+/Ca2+ exchange current in rat ventricular myocytes

AIM: To study the effects of E-4031 on the Na+/Ca2+ exchange currents (INa/Ca). METHODS: The quasi-steady state current-voltage relationship from the isolated rat ventricular myocytes was measured using whole-cell voltage-clamp techniques with a ramp pulse protocol. RESULTS: At potential of mV, E-4031 5, 10, and 20 mumol.L-1 increased Ni(2+)-sensitive current from (0.48 +/- 0.12), to (0.78 +/- 0.20), (0.96 +/- 0.16), and (1.15 +/- 0.13) pA/pF, respectively; tetradecanoylphorbol acetate (TPA) 50 nmol.L-1 increased Ni(2+)-sensitive current from (0.60 +/- 0.16) to (1.33 +/- 0.25) pA/pF. Tamoxifen 20 mumol.L-1 completely prevented the current changes induced by E-4031 and TPA. CONCLUSION: E-4031 stimulates the Na+/Ca2+ exchange via a protein kinase C-dependent pathway.     

Decreases of voltage-dependent K^＋ currents densities in ventricular myocytes of guinea pigs by chronic oxidant stress

INTRODUCTION Intracellular K concentration plays an importantrole in the regulation of apoptosis process[1]. ExcessiveK efflux and intracellular K depletion may be respon-sible for the cell shrinkage and apoptotic death[2,3]. Cel-lular K homeostasis is maintained by K efflux and K uptake mechanism. Voltage-dependent K currents arethe major pathways for the K efflux, which indicatesthat voltage-dependent K currents are involved in theapoptosis. Several studies reported th…     

Electrophysiologic effects of an antiarrhythmic agent, bidisomide, on sodium current in isolated rat ventricular myocytes: comparison with mexiletine and disopyramide.

The effects of bidisomide, an antiarrhythmic agent, on sodium current (I(Na)) in isolated rat ventricular myocytes were investigated using a whole cell voltage clamp method. Bidisomide blocked I(Na) with a Ki of 214 microM at a holding potential of -140 mV. The blockade of I(Na) was enhanced at a less negative holding potential of -100 mV with a Ki of 21 microM. Bidisomide shifted the steady state inactivation curve to a negative potential direction by 20 mV without a significant change in the slope factor. Bidisomide slowed the time course of recovery of I(Na) at a holding potential of -140 mV with a slow recovery phase. The time constant of recovery phase for bidisomide, disopyramide and mexiletine were 2703, 1858 and 757 ms, respectively. The development of the block of I(Na) consisted of two phases in the presence of bidisomide. The fast and slow time constants were 11 and 648 ms. Bidisomide produced a use-dependent block of I(Na) when the depolarizing pulse was repeated at 1-3 Hz. Our results indicate that bidisomide binds to rat cardiac sodium channels and that the dissociation kinetics of bidisomide from the inactivated sodium channel is slower than that of disopyramide.     

Treatment with irbesartan counteracts the functional remodeling of ventricular myocytes from hypertensive rats

Changes in electrophysiological (action potential prolongation, decrease in transient outward current I(to), occurrence of the hyperpolarization-activated current I(f)) and contractile properties develop in hypertrophied ventricular myocytes, likely implicated in the increased propensity to arrhythmias. Angiotensin II is a key signal for myocyte hypertrophy; the effect of 8-week treatment with irbesartan, a type 1 angiotensin II receptor (AT(1)) antagonist, on cardiac remodeling was tested. Sixteen-month-old hypertensive rats (SHRs) were treated with irbesartan (20 mg/kg/d) or saline for 8 weeks. At the end of treatment, systolic blood pressure and heart weight to body weight ratio were reduced in irbesartan-treated compared with nontreated SHRs. Electrical and contractile properties were measured in isolated ventricular myocytes, by patch-clamp or video-dimension analysis, respectively. Action potential duration was significantly shorter in irbesartan-treated than in nontreated SHRs (at -60 mV: 119 +/- 24 ms vs 187 +/- 20 ms); correspondingly, maximal I(to) density was larger in irbesartan-treated than in nontreated SHRs (25.4 +/- 2.8 pA/pF vs 18.5 +/- 1.5 pA/pF). Maximal specific conductance of I(f) was lower in irbesartan-treated vs nontreated SHRs (24.8 +/- 3.0 pS/pF vs 35.2 +/- 4.0 pS/pF). Finally, the relaxation rate of shortening in field-stimulated intact myocytes was significantly faster in irbesartan-treated than in nontreated SHRs (7.3 +/- 0.5/s vs 5.7 +/- 0.3/s). Thus, AT(1) blockade with irbesartan, at an oral daily dosage that gave a slight but significant reduction of systolic blood pressure, largely counteracts the development of myocyte hypertrophy and associated functional alterations.     

胍丁胺对大鼠心室肌细胞L—钙通道电流的影响

目的:观察胍丁胺(Agm)对大鼠心室肌细胞L-型钙通道电流(I_(Ca-L))的影响.方法:以酶解法制备单个心室肌细胞.应用全细胞膜片箝技术记录大鼠单个心室肌细胞钙通道电流.结果:(1)Agm(0.5,1,2mmol/L)可浓度依赖性地降低电压依赖性激活I_(Ca-L)(pA)峰值,其值从1451±236 (对照组)到937±105(n=8,P<0.05),585±74(n=8,P<0.01),和301±156(n=8,P<0.01).(2)Agm 1 mmol/L使用依赖性地阻滞I_(Ca-L)·1 Hz时抑制率为53％±12％(P<0.05),3Hz时为69％±11％(P<0.01).(3)Agm使I-V曲线上移,但对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Agm 1 mmol/L作用下,半数激活电压(V_(0.5)和斜率参数(k)与对照组相比均无显著性差异.V_(0.5)分别为(-20.2±2.5)mV和(-20.5±2.7)mV,k分别为(3.2±0.4)mV和(3.0±0.5)mV.(4)Agm 1 mmol/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(-32±6)mV和(-40±5)mV,k分别为(7.6±O.9)mV和(12.5±1.1)mV(P<0.05).(5)Agm 1mmol/L还使I_(Ca)从失活状态下恢复明显减慢.结论:Agm抑制I_(Ca-L),并主要作用于L-型钙通道的失活状态,表现为钙通道失活加速和从失活状态下恢复减慢.     

充血性心衰病人心房肌细胞瞬间外向钾电流和超快速延迟整流钾电流的特征

AIM: To study the properties of transient outward K+ current (Ito) and ultra-rapid delayed rectifier K+ current (IKur) in isolated human atrial myocytes from patients with congestive heart failure (CHF). METHODS: Single cells were isolated from CHF patients with collagenase and protease. Ito and IKur were recorded using whole cell patch-clamp technique. RESULTS: The activation and inactivation of I(to) were voltage-dependent and time-dependent. The half-activation and half-inactivation voltage were (15 +/- 12) mV and (-45 +/- 4) mV respectively. When membrane potential went up from -40 mV to +60 mV, the activation time constant means decreased from (6.9 +/- 2.3) ms to (1.40 +/- 0.20) ms, while the inactivation time constant means decreased from (69 +/- 17) ms to (21 +/- 14) ms. Otherwise, the mean reactivation time constants was (125 +/- 65) ms when the membrane potential was held at -80 mV, but the recovery was not complete during the interval observed. Ito showed less frequency-dependent reduction at test frequency between 0.2-2 Hz. Compared with Ito, the activation of IKur only showed voltage-dependence, without time-dependence. Its mean current densities was (3.4 +/- 0.7) pA/pF when test potential was +60 mV. The half activation voltage of IKur was (23 +/- 14) mV. No clear frequency-dependence was observed at the same frequency range of Ito either. CONCLUSION: I(to) and IKur are important outward potassium channel currents in isolated human atrial myocytes from CHF patients and they have different kinetic properties.     

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。     

Heterogeneity of the properties of INa in epicardial and endocardial cells of rat ventricle

1. Ventricular I(Na) heterogeneity was investigated in adult rat hearts. Differences in transient outward potassium current (Ito) were used to confirm isolation of subepicardial and subendocardial cells. Mean peak Ito was 6.0 +/- 0.7 and 1.6 +/- 0.45 pA/pF in epicardial and endocardial cells, respectively (P < < 0.01). 2. Maximum sodium conductance was smaller in subendocardial cells compared with subepicardial cells (2.39 +/- 0.11 vs 2.78 +/- 0.12 nS/pF, respectively; n=17 for both; 0.01 < P < 0.05) and 50% activation occurred at a slightly more negative potential (-47.6 +/- 0.8 vs -44.9 +/- 0.9 mV, respectively; n=10 for both; 0.01 < P < 0.05). 3. The potential for 50% inactivation was not significantly different in subepicardial compared with subendocardial cells (72.2 +/- 1.0 vs 72.8 +/- 2.2 mV, respectively; n=17 for both; NS). 4. Persistent sodium current density appeared smaller in subendocardial (n =19) compared with subepicardial (n=11) cells (at a test potential of -25 mV current, density was 0.118 +/- 0.041 vs 0.144 +/- 0.085 pA/pF, respectively), although this was not statistically significant due to large variability between cells. 5. Mathematical modelling of the cardiac action potential indicated that the combined effects of differences in current density and voltage dependence of sodium currents are unlikely to contribute to ventricular action potential heterogeneity between epicardial and endocardial cells.     

Electrophysiological effects of bimoclomol in canine ventricular myocytes

Concentration-dependent effects of bimoclomol, a novel heat shock protein (HSP) coinducer, were studied on the parameters of action potential and transmembrane ionic currents in enzymatically dispersed canine ventricular cardiomyocytes using conventional microelectrode and whole cell voltage clamp techniques. Bimoclomol (10-100 microM) decreased the maximum velocity of depolarization (Vmax) and amplitude of action potentials in a concentration-dependent manner. These effects were fully reversible after a 5-min period of washout in drug-free medium. Action potential duration measured at 50% or 90% level of repolarization (APD-50 and APD-90, respectively) was markedly shortened by bimoclomol. Both APD-50 and APD-90 were decreased, but the reduction in APD-50 was more pronounced. The APD-shortening effect of bimoclomol was significantly reduced in the presence of 20 nM charybdotoxin (inhibitor of the Ca-dependent K current) or 0.5 mM anthracene-9-carboxylic acid (inhibitor of the Ca-dependent Cl current) or 1 microM glibenclamide (inhibitor of the ATP-sensitive K current). In the presence of anthracene-9-carboxylic acid, APD-90 was lengthened by bimoclomol. The APD-shortening effect of bimoclomol was also partially antagonized by chelation of intracellular Ca2+ by application of the cell permeant form of BAPTA, or when using 10 mM EGTA-containing patch pipettes to record action potentials. The Vmax-depressant effect of bimoclomol was not affected by charybdotoxin, anthracene-9-carboxylic acid, glibenclamide, or BAPTA load. In voltage clamped cardiomyocytes bimoclomol (100 microM) had no effect on the amplitude of I(Ca), but decreased significantly the inactivation time constant of I(Ca) (from 19.8+/-1.6 ms to 16.8+/-1.2 ms at 0 mV). Bimoclomol also decreased significantly the amplitude of I(K1) (from -20.5+/-1.1 pA/pF to -16.6+/-0.8 pA/pF at -135 mV), causing reduction in slope of the negative branch of the I-V curve. At positive potentials, however, bimoclomol increased outward current. The bimoclomol-induced current, therefore, was studied in the presence of BaCl2, when I(K1) current was blocked. The bimoclomol-induced current had a reversal potential close to -90 mV. Bimoclomol (100 microM) had no effect on the amplitude or kinetic properties of the transient outward K current (I(to)) and the delayed rectifier K current (I(K)). It is concluded that bimoclomol exerts both Ca-independent (inhibition of I(Na) and I(K1), activation of the ATP-sensitive K current) and Ca-dependent effects (mediated by Ca-activated Cl and probably K currents) in canine ventricular myocytes.     

白藜芦醇对豚鼠心室肌细胞L型钙通道的影响

目的研究白藜芦醇(resveratrol,RES)对豚鼠心室肌细胞L型钙通道的影响。方法酶解法分离单个豚鼠心室肌细胞,采用全细胞膜片钳技术记录白藜芦醇对豚鼠单个心室细胞L型钙通道电流(ICa-L)的影响。结果不同浓度的RES明显抑制ICa-L,1、10、100μmol.L-1L的RES使其峰电流密度从(12.96±1.48)pA/pF减少到(11.36±1.59)、(9.96±1.51)和(7.77±0.68)pA/pF(n=6,P<0.01),冲洗后可恢复至(11.85±0.83)pA/pF。RES可使ICa-L的I-U关系曲线上移,其形状和峰值电压保持不变;RES还可使通道的激活曲线右移,但失活曲线和失活恢复时间无改变。结论白藜芦醇通过延长L型钙通道激活过程而明显抑制ICa-L,减少细胞外的钙离子内流,延长有效不应期,从而发挥抗心律失常作用。     

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。     

M_3受体激动剂对豚鼠心室肌细胞L型钙通道的影响

目的研究M3受体激动剂胆碱对豚鼠心室肌细胞L型钙通道的影响。方法应用全细胞膜片钳技术记录M3受体激动剂胆碱对豚鼠单个心室肌细胞L型钙通道电流(ICa-L)的影响;采用激光扫描共聚焦技术观察细胞内钙离子的变化。结果应用10 mmol.L-1胆碱使豚鼠心室肌细胞ICa-L密度从(9.02±0.82)pA/pF减少到(5.61±0.55)pA/pF(n=4,P<0.01),5 nmol.L-14-DAMP能够使其恢复至(8.12±0.65)pA/pF(n=4,P<0.01);10 mmol.L-1胆碱抑制KCl除极诱导的心肌细胞内钙的升高,从(2.76±0.05)降至(1.37±0.05)倍(n=8,P<0.01),5 nmol.L-14-DAMP可以阻断该作用(n=8,P<0.01)。结论M3受体激动剂胆碱通过延长L型钙通道激活过程而明显抑制ICa-L,减少细胞外的钙离子内流,降低心肌细胞内钙,从而发挥抗心律失常作用。     

Anti-ischemic compound KC 12291 prevents diastolic contracture in isolated atria by blockade of voltage-gated sodium channels

Several lines of evidence support a fundamental role for voltage-gated sodium channels in mediating ischemic Na rise. We examined the effect of the novel anti-ischemic compound KC 12291 on veratridine-stimulated and lysophosphatidylcholine (LPC)-induced sustained sodium current (I(NAL)) mediated by sodium channels in isolated myocytes obtained from guinea-pig atria, by using the whole-cell patch-clamp technique. We also analyzed the effect of KC 12291 on veratridine- and LPC-induced contractures in isolated guinea-pig atria. Veratridine as well as LPC increased I(NAL) measured at 20 ms of a 2 s pulse evoked from -100 to -30 mV (47.5 and 12 pA/pF in the presence of 40 microM veratridine and 10 microM LPC, respectively, vs. 6.7 pA/pF under control conditions). A significant reduction by KC 12291 in the quantity of charge carried by veratridine-stimulated I(NAL) in the range of test potentials between -50 mV and +10 mV was observed and similar effects were obtained on LPC-induced I(NAL). Thus, the quantity of charge carried by LPC-induced I(NAL) over a 2 s pulse to -30 mV was reduced by 48% in the presence of 10 microM KC 12291 vs. a reduction by 50% of veratridine-stimulated I(NAL) at the same test potential. Veratridine- and LPC-induced submaximal contractures in isolated atria were significantly inhibited by KC 12291 in a concentration-dependent manner, with an IC of 0.55 microM and 0.79 microM, respectively. The data indicate that veratridine- and LPC-induced increases in diastolic tension are inhibited by KC 12291 by a mechanism that involves blockade of voltage-gated sodium channels mediating sustained sodium current.     

Bisoprolol inhibits sodium current in ventricular myocytes of rats with diastolic heart failure

1. Changes in sodium currents (I(Na)) in heart failure contribute to cardiac electrophysiological alterations and, thereby, to ventricular arrhythmias. Bisoprolol has anti-arrhythmic effects, but its direct effect on I(Na) in cardiac cells remains unclear. Accordingly, in the present study we investigated the effects of bisoprolol on ventricular I(Na) in diastolic heart failure (DHF) and normal rats. 2. The DHF model was produced by abdominal aortic coarctation for 4 weeks and single ventricular myocytes were isolated by enzymatic dissociation. The electrophysiological actions of bisoprolol on I(Na) currents were investigated using a whole-cell patch-clamp technique. 3. The membrane capacitance of rats in the DHF group was significantly greater than that of the control group and the current-voltage curve was simultaneously shifted downward. Bisoprolol concentration-dependently decreased I(Na) in ventricular myocytes of both groups (at -45 mV), with IC(50) values of 19.53 +/- 0.06 and 40.78 +/- 0.03 micromol/L in the control and DHF groups, respectively. 4. In both groups, the current-voltage curves were shifted upwards, whereas activation potentials, peak currents and reversal potentials showed no significant changes. At -45 mV, the descent ratio of current densities in the DHF group was lower than that of the control group. In both groups, inactivation curves were shifted to more negative potentials, but activation curves and recovery curves were not altered. Changes in the half-inactivation voltage, V(0.5), and the slope of the inactivation curve, S, were similar for both groups. 5. In conclusion, bisoprolol concentration-dependently decreases I(Na) in ventricular myocytes of DHF and normal rats, which could be responsible, at least in part, for its anti-arrhythmic effects.