The Effect of Levobunolol Hydrochloride on the Calcium andPotassium Channels in Isolated Ventricular Myocytes of Guinea Pig

The effects of levobunolol hydrochlorid (Bun) on the type L calciumchannel currents (Ica) and delayed rectifier potassium channel currents (Ik) in isolated ventricular myocytes of guinea pig were studied by using patch clamp wholecell recording techniques. The results were showed that: 1) Bun caused a dosedependent decrease in Ica and a dose-dependent increase in Ik of the ventricular myocytes.The threshold concentrations of Bun for Ica and Ik were 10-8 mol/L and10-7 mol/L respectively. The maximum effective concentration of Bun for both Ica and Ik was 3 × 10-5 mol/L, and half-maximal concentration was 3 × 10-6 mol/L;2 ) Ik was blocked by 2× 10-6mol/L tetraethylammonium (TEA). A concentration of 3 × 10-6 mol/L Bun showed a decreasing effect on the Ica as revealed by the current-voltage relationship curve, i. e., Bun caused an elevation of the curve; 3)When Ica was blocked by 2 × 10-6 mol/L Isoptin (Verapamil), at a concentrationof 3 × 106- mol/L Bun showed an increasing effect on Ik and the effect could be blocked by TEA. The above-mentioned results indicated that Bun had an inhibito-ry effect on Ica and a fascilitatory effect on Ik The results suggested that themolecular mechanisms of antihypertensive, heart rate slowing and β-receptorblocking effects of Bun might be due to decrease of Ica and increase of Ik.

CLOFILIUM, A POTENT BLOCKER OF SODIUM AND CALCIUM CHANNELS IN GUINEA-PIG VENTRICULAR MYOCYTES

The unsatisfactory results of clinical trials with class-Ⅰ antiarrhythmic drugs have prompted a renaissance of interest in compounds with class-Ⅲ antiarrhythmic action. In the present, we have reevaluated the class-Ⅲ antiarrhythmic ef-

Blocking Effect of Salvianolic Acid A on Calcium Channels in Isolated Rat Ventricular Myocytes

Objective： To study the effect of salvianolic acid A （SAA） on L-type calcium current （I-CaL） in isolated ventdcular myocytes of Sprague-Dawley rats. Methods： SPA powder was dissolved in normal Tyrode＇s solution to reach the concentrations of 1, 10, 100, and 1000 μmol/L. The traditional whole-cell patch-clamp recording technique was employed to evaluate the effects of SAA on I-CaL in single ventricular myocytes which were prepared by Langendorff perfusion apparatus from Sprague-Dawley rats. Results： SPA （1, 10, 100, and 1000 μmol/L） inhibited I-CaL peak value by 16.23%± 1.3% （n=6, P〈0.05）, 22.9% ± 3.6% （n=6, P〈0.05）, 53.4% ± 3.0% （n=8, P〈0.01）, and 62.26% ± 2.9% （n=8, P〈0.01）, respectively. SAA reversibly inhibited I-CaL in a dose-dependent manner and with a half-blocking concentration （IC50） of 38.3 μmol/L. SAA at 100 μmol/L elevated the I-V curve obviously, and shifted the half-active voltage （V0.5） from （-15.78± 0.86） mV to （-11.24 ± 0.77） mV （n=6, P〈0.05） and the slope （K） from 5.33 ±0.74 to 4.35±0.74 （n=6, P〉0.05）. However, it did not alter the shapes of I-V curve, steady-state inactivation curve, or recovery from inactivation curve. Conclusions： SAA inhibited I-CaL in a dose-dependent manner. It shifted the steady-state activation curve to a more positive voltage, which indicated that the drug affected the activated state of calcium channels, and suggested that the Ca2. antagonistic effect of SPA be beneficial in the treatment of myocardial ischemia reperfusion injury.

Voltage- and Use-dependent Effect of 7-chlor-benzylte-trahydropalmatine on Sodium Currents in Guinea Pig Ventricular Myocytes

The whole-cell patch-clamp technique was employed to obtain information about the voltage-dependence and kinetics of interaction of 7-chlor-benzylte-trahydropalmatine (7-Cl-BTHP) with cardiac sodium channels. 7-Cl-BTHP (30 mol/L) significantly decreased the peak sodium current (from 7. 8±1. 8 nA to 5. 3±1. 4 nA, P<0. 01, n=5), without producing a shift of the current-voltage curve. It shifted the inactivation curves of sodium current to hyperpolarized potentials, and the V(0.5) was shifted from - (82. 5±2. 5) mV to - (95±2.4) mV (P <0. 05, n=4). 7-Cl-BTHP produced a significant use-dependent effect that was proportional to the duration of the voltage step. In addition, 7-Cl-BTHP slowed the recovery of sodium channel from inactivation, which could explain its use-dependent effects on sodium current. The characteristics of 7-Cl-BTHP blockage suggest that this agent binds preferentially to inactivated sodium channels.

Differentially expressed phosphoproteins in diazoxide-pretreated ventricular myocytes by two-dimensional electrophoresis and mass spectrometry in vitro

Objectives To analyze and identify differentially expressed phosphoproteins associated with mitochondrial KATP channel opening. Methods： Adult rat ventricular myocytes were isolated, cultured, and identified, and pretreated without or with 100 μmol/L diazoxide for 10 min. Phosphoproteins prepared and enriched from the control and diazoxide-pretreated cells were separated by two-dimensional gel electrophoresis （2-DE） followed by sliver staining. The obtained interesting phosphoproteins were further identified by mass spectrometry. Results. Associated with diazoxide preconditioning, the proteins of chaperonin containing TCP-1 and hypothetical protein XP-346548 were phosphorylated significantly （P〈0. 01）, while the 94-kDa glucose-regulated protein, calpactin I heavy chain and ferritin were dephosphorylated markedly （P〈0. 01）. Conclusion： These findings suggest that cardiomyocytes undergo significant posttranslational modification via phosphorylation in a multitude of proteins in order to respond diazoxide preconditioning, and these phosphorylated protein may mediate the downstream signaling of cardioprotection by mitochondrial KATp channel opening induced by ischemic preconditioning.

Differences of promethazine and terfenadine on ion channels in guinea pig ventricular myocytes

Promethazine, a first generation antihistamine,has an antiarrhythmic effect on ischemia-reperfusion inducing arrhythmias^1 and experimental arrhythmias.^2 However, terfenadine as a second generation of antihistamine, has been reported to elicit hypotension, bradycardia, prolongation of the QTc interval and torsades de pointes （TdP） like ventricular arrhythmia.^3 This may be due to the blockage on rectifier postassium current （Ik） of terfenadine, resulting in the prolongation of the action potential duration （APD） and dispersion of the repolarization duration, which might provoke a specific form of polymorphic ventricular tachydysrhythmia, i.e. TdP.^4 In clinical practice,however, the class Ⅲ antiarrhythmic agents, which target on the lk and prolong the action potential duration and QTc interval, rarely lead to arrhythmias.Other actions must be considered to underlie the arrhythmogenic tendency of terfenadine besides its inhibition on Ik. Though both promethazine and terfenadine block the H1 receptor, there must be a different pharmacology profile between the two compounds on ion channels of cardiac myocytes.Whole-cell patch clamp technique was used to investigate the effects of these two antagonists of the H1 receptor on the main ion currents in cardiac electrical activities.

Effect of didrovaltrate on l-calcium current in rabbit ventricular myocytes

OBJECTIVE:To investigate the effect of didrovaltrate on L-type calcium current(I Ca-L) in rabbit ventricular myocytes.METHODS:We used the whole cell patch clamp recording technique.RESULTS:Didrovaltrate at concentrations of 30 μg/L and 100 μg/L significantly decreased peak I Ca-L(I Ca-Lmax) from(6.01±0.48) pA/pF to(3.45±0.27) pA/pF and(2.16 ± 0.19) pA/pF(42.6% and 64.1%,n=8,P< 0.01),respectively.Didrovaltrate shifted upwards the current-voltage curves of I Ca-L without changing their active,peak and reverse potentials.Didrovaltrate affected the steady-state inactivation of I Ca-L.The half activation potential(V 1/2) was significantly shifted from(-26 ± 2) to(-36 ± 3) mV(n=6,P<0.05),with a significant change in the slope factor(k)(from 8.8 ± 0.8 to 11.1 ± 0.9,n=6,P<0.05).Didrovaltrate did not affect the activation curve.CONCLUSION:Didrovaltrate blocks I Ca-L in a concentration-dependent manner and probably inhibits I Ca-L in its inactive state,which may contribute to its cardiovascular effect.

The Effect of Benzyltetrahydropalmatine (BTHP) on Action Potentials and the Two Components of Delayed Rectifying Potassium Currents in Guinea Pig Ventricular Myocytes

The effects of BTHP on Ca 2+ independent action potential and the two components of delayed rectifier potassium currents were studied in guinea pig single ventricular myocytes by using whole cell patch clamp technique. BTHP 30 μmol·L -1 significantly prolonged APD 90 from 143±16 ms to 184±21 ms ( P 【0.01, n=5) without affecting either the RP or APA, and the APD prolonging effects of BTHP were independent of extracellular Ca 2+ . BTHP inhibited both I kr (IC 50 =7 9 μmol·L -1 ) and I ks (IC 50 =22 4 μmol·L -1 ) in a concentration dependent fashion. The results demon strated that BTHP had no obvious selectivity for I kr and I ks .

Blocking effect of Puerarin on calciu m channel in isolated guineapig ventricular myocytes

To identify whether Puerarin (Puer) has blocking effects on L type calcium channel Methods We used whole cell recording of patch clamp techniques to analyse calcium channel current in ventricular myocytes isolated from Langendorff guinea pig hearts by collagenase Results In control group, peak calcium channel current was decreased by 10 6% and 29 8% at 5, 10?min of recording time, respectively For the same period, 0 1?mmol/L Puer reduced calcium current by 23 9% and 72 4% 0 1 and 1?mmol/L Puer inhibited the amplitude of peak Calcium channel current by 40 6% and 63 2% after perfusing for 10?min Compared with control group in which “rundown' phenomenon was observed, Puer also demonstrated its blocking effect on L type channel While washout of Puer with perfusing solution, calcium channel current went down further instead of recovery Current voltage (Ⅰ Ⅴ) curves showed that the levels of calcium channel current were obviously decreased by Puer (both 0 1?mmo/L and 1?mmo/L) form -40?mV to+10?mV Conclusion Puer has blocking effect on L type calcium channel in a concentration dependent manner

Study of transmembrane La^(3+) movement in rat ventricular myocytes by the patch-clamp technique

We have studied transmembrane La3+ movement in rat ventricular myocytes for the first time by using the whole-cell patch-clamp recording mode. La3+ (0.01-5.0 mmol/L) could not bring out inward currents through the L-type calcium channel in rat ventricular myocytes, while it could enter the cells by the same way carried by 1μmo1/L ionomycin. When the outward Na+ concentration gradient is formed, La3+ can enter the cells via Na-Ca exchange, and the exchange currents increase with the increase of external La3+ concentrations. But compared with Na-Ca exchange currents in the same concentration, the former is only 14%-38% of the latter. The patch-clamp experiment indicates that La3+ normally can not enter ventricular myocytes through L-type calcium channel, but it can enter the cells via Na-Ca exchange.

Effects of remifentanil on intracellular Ca^2＋ and its transients induced by electrical stimulation and caffeine in rat ventricular myocytes

Background Preconditioning with remifentanil confers cardioprotection. Since Ca^2＋ overload is a precipitating factor of injury, we determined the effects of remefentanil on intracellular Ca^2＋ （[Ca^2＋]i） and its transients induced by electrical stimulation and caffeine, which reflects Ca^2＋ handling by Ca^2＋ handling proteins, in rat ventricular myocytes. Methods Freshly isolated adult male Sprague-Dawley rat myocytes were loaded with Fura-2/AM and [Ca]i was determined by spectrofluorometry. Remifentanil at 0.1-1000 μg/L was administered. Ten minutes after administration, either 0.2 Hz electrical stimulation was applied or 10 mmol/L caffeine was added. The [Ca^2＋]i, and the amplitude, time resting and 50% decay （t50） of both transients induced by electrical stimulation （E[Ca^2＋]i） and caffeine （C[Ca^2＋]i） were determined. Results Remifentanil （0.1-1000.0 μg/L） decreased the [Ca^2＋]i in a dose-dependent manner. It also decreased the amplitude of both transients dose-dependently. Furthermore, it increased the time to peak and tso of both transients dose-dependently. Conclusion Remifentanil reduced the [Ca^2＋]i and suppressed the transients induced by electrical stimulation and caffeine in rat ventricular myocytes.

Sex Difference in the Repolarization Currents of Rabbit Ventricular Cells

The current difference between male and female rabbit ventricular myocytes was investigated for elucidating the mechanism of longer QT interval and higher incidence of drug-associated torsade de pointes in female rabbits than in male rabbits. Whole cell patch clamp technique was used to record APD, I_to, I_K,tail, I_K1 and I_Ca,L of myocytes from left ventricular apex. There was no difference in the membrane capacitance between male and female rabbit myocytes. APD_90 was longer in female rabbits (560.4±26.5 ms, n=15) than in male ones (489.0±20.7 ms, n=14), P<0.05. In female rabbit myocytes, I_K,tail, I_to, I_K1 and I_Ca,L were 0.71±0.05 pA/pF (n=17), 8.28±1.03 pA/pF (n=18), 24.5±3.6 pA/pF (n=12) and 9.0±2.3 pA/pF (n=15) respectively. In male rabbit myocytes, they were 0.84±0.07 pA/pF (n=18), 8.60±1.20 pA/pF (n=18), 25.9±4.5 pA/pF (n=14) and 9.3±2.6 pA/pF (n=16) respectively. I_K,tail in female rabbits was significantly lower than that of male rabbits (P<0.05), but there was no difference in I_to, I_K1 and I_Ca,L between male rabbits and female rabbits (P>0.05). The lower I_K,tail of female rabbit myocytes may contribute to the longer repolarization and the higher incidence of drug-associated torsade de pointes.

Effect of gingerol on colonic motility via inhibition of calcium channel currents in rats

AIM: To investigate the effect of gingerol on colonic motility and the action of L-type calcium channel currents in this process.METHODS: The distal colon was cut along the mesenteric border and cleaned with Ca^(2+)-free physiological saline solution. Muscle strips were removed and placed in Ca^(2+)-free physiological saline solution, which was oxygenated continuously. Longitudinal smooth muscle samples were prepared by cutting along the muscle strips and were then placed in a chamber. Mechanical contractile activities of isolated colonic segments in rats were recorded by a 4-channel physiograph. Colon smooth muscle cells were dissociated by enzymatic digestion. L-type calcium currents were recorded using the conventional whole-cell patch-clamp technique.RESULTS: Gingerol inhibited the spontaneous contraction of colonic longitudinal smooth muscle in a dose-dependent manner with inhibition percentages of 13.3% ± 4.1%, 43.4% ± 3.9%, 78.2% ± 3.6% and 80.5% ± 4.5% at 25 μmol/L, 50 μmol/L, 75 μmol/L and 100 μmol/L, respectively(P < 0.01). Nifedipine, an L-type calcium channel blocker, diminished the inhibition of colonic motility by gingerol. Gingerol inhibited L-type calcium channel currents in colonic longitudinal myocytes of rats. At a 75 μmol/L concentration of gingerol, the percentage of gingerolinduced inhibition was diminished by nifedipine from 77.1% ± 4.2% to 42.6% ± 3.6%(P < 0.01). Gingerol suppressed IBa in a dose-dependent manner, and the inhibition rates were 22.7% ± 2.38%, 35.77% ± 3.14%, 49.78% ± 3.48% and 53.78% ± 4.16% of control at 0 m V, respectively, at concentrations of 25 μmol/L, 50 μmol/L, 75 μmol/L and 100 μmol/L(P < 0.01). The steady-state activation curve was shifted to the right by treatment with gingerol. The value of half activation was-14.23 ± 1.12 m V in the control group and-10.56 ± 1.04 m V in the 75 μmol/L group(P < 0.05) with slope factors, Ks, of 7.16 ± 0.84 and 7.02 ± 0.93(P < 0.05) in the control and 75 μmol/L groups, respectively. However, the steady-state inactivation curve was not changed, with a half-inactivation voltage, 0.5 V, of-27.43 ± 1.26 m V in the control group and-26.56 ± 1.53 m V in the 75 μmol/L gingerol group(P > 0.05), and a slope factor, K, of 13.24 ± 1.62 in the control group and 13.45 ± 1.68(P > 0.05) in the 75 μmol/L gingerol group.CONCLUSION: Gingerol inhibits colonic motility by preventing Ca^(2+) influx through L-type calcium channels.

A Clinical Study of Reversing Left Ventricular Hypertrophy in Hypertensive Patients by Adalat

Fourteen outpatients (10 men, 4 women, mean age 52.6 yrs) suffered from essential hypertension complicated with left ventricular hypertrophy (LVH) detected by echocardiography were treated with Adalat 30 mg daily orally. After 3 months administration, casual high blood pressue was satisfactorily controlled. Both thickness of inter ventricular septum and left ventricular posterior wall were decreased (1.47 cm vs 1.34 cm P<0.01, 1.43 cm vs 1.32 cm P<0.01). Left ventricular mass (LVM) and left ventricular mass index (LVMI) calculated according to Devereux corrective formula were significantly reversed (279.4 g vs 247.4 g P<0.01, 162.7 g/m 2 vs 146.5 g/m 2 P<0.01). Meanwhile, cardiac performance was assessed, and the results demonstrated that Adalat could maintain left ventricular systolic function and improve left ventricular diastolic function which was resulted from regression of LVH. No side effects of Adalat were present in the study patients.

脓毒症心肌病对大鼠心室肌细胞的损伤及维生素C的干预效果

目的:研究脓毒症对大鼠心肌的损伤及维生素C的干预效果。方法:选取90只SD雄性大鼠随机分成三组,将其中两组进行脓毒症造模,一组予维生素C干预(A组)、另一组作为脓毒症组(B组)及第三组为对照组(C组),造模成功后24 h和48 h检测降钙素原(procalcitonin,PCT)、脂多糖(lipopolysaccharide,LPS)及超氧化物歧化酶(superoxide dismutase,SOD)水平;造模后24 h检测大鼠左室射血分数以及左心室收缩末期和舒张末期容积和心肌细胞动作电位及离子通道电压与密度变化。结果:A组及B组PCT、LPS均升高且高于C组,而B组在造模后48 h的PCT及LPS高于A组。超声提示A、B两组大鼠左室射血分数、收缩及舒张末期容积均降低,但B组更为显著;与C组相比,A、B两组的心肌细胞动作电位显著延长、而B组延长更为明显;与C组相比,A组与B组的I_(Ca-L)和I_(to)密度明显降低、B组更为显著(均P<0.05);造模后48 h SOD检测发现A组较C组相比升高、B组与C组比较降低(均P<0.05)。结论:脓毒症大鼠PCT、LPS升高,维生素C干预可以降低其水平;脓毒症大鼠SOD降低,维生素C干预可以减轻SOD降低水平。脓毒症大鼠心脏功能下降,且心肌细胞动作电位明显延长,同时脓毒症大鼠I Ca-L和I to密度降低,而进行维生素C干预后均可改善。

葛根素对大鼠心肌细胞L型钙离子通道的影响

目的 :观察葛根素对大鼠L型钙离子通道的作用。方法 :恒流Langendorff灌流 ,I型胶原酶解分离 ,全细胞膜片钳技术记录离子电流。结果 :2 .4mmol·L- 1葛根素可以抑制单个大鼠心室肌细胞L型钙离子通道电流 ,且成时间依赖性 ;葛根素可以促进L型钙通道电流 电压 (I V)曲线的上移。结论 :葛根素可以抑制大鼠心室肌细胞的L型钙离子通道电流 。

参松养心胶囊对心室肌细胞钾通道的影响

目的观察参松养心胶囊干粉提取溶液对大鼠单个心室肌细胞内向整流钾电流(IK1)、瞬时外向钾电流(Ito)以及豚鼠心肌细胞延迟整流钾电流(Ik)的影响。方法用酶解法分离单个心室肌细胞,并用全细胞膜片钳记录技术。结果当药物浓度0.5%时,可以使大鼠心肌细胞IK1内向成分降低,使-100mV时IK1电流密度从(-10.8±1.8)pA/pF降至(-7.2±2.1)pA/pF,平均抑制率为(33.1±16.9)%(n=11,P<0.05),但不改变电流的翻转电位及整流特性。药物同时对Ito电流的瞬时成分有抑制作用,60mV时Ito电流密度从(-19.8±7.1)pA/pF降至(-10.0±3.9)pA/pF,平均抑制率为(50.6±10.8)%(n=6,P<0.05),稳态失活曲线左移,失活后恢复时间常数增大。药物浓度0.5%时,对Ik有电压依赖性抑制作用,50mV时对尾电流峰值的抑制率为(30.8±1.1)%(n=5,P<0.05)。结论参松养心胶囊干粉提取溶液对IK1,Ito和Ik均具有不同程度的阻滞作用。这种多离子通道阻滞作用不仅使参松养心胶囊具有广谱的抗心律失常疗效,减少致心律失常的副作用,对Ito的阻滞效应还将显示其独特的抑制2相折返的作用,值得对其作更深入和广泛的研究。

葛根素对豚鼠心室肌细胞钾离子通道的影响

目的 :观察葛根素对豚鼠单个心室肌细胞钾离子通道的影响。方法 :采用内面向外膜片钳单通道记录技术。结果 :葛根素 2 0 μmol/L ,4 0 μmol/L ,80 μmol/L对单个心肌细胞钾离子通道的开放概率 (P0 )有抑制作用 ,在 80μmol/L时 ,P0 值从 0 .86 7± 0 .13降至 0 .0 19± 0 .0 1,与用药前比较有显著差异 (n =5 ,P <0 .0 1)。结论

莲心碱对豚鼠心室肌细胞动作电位及钠与钙电流的影响

为探讨莲心碱 (liensinine,L ien)对心肌离子流的影响及抗心律失常作用机制。采用全细胞膜片钳技术 ,记录了 L ien对单个豚鼠心肌细胞动作电位 (AP)及纳电流 (INa)与 L -型钙电流 (ICa- L)的影响。 L ien 3～ 30μmol/ L 可剂量依赖性地降低 AP幅度 (APA)、静息电位 (RP) ,延长 AP时程。 L ien10 ,30 μm ol/ L 分别使 INa及 ICa- L从给药前的 (8.6± 2 .3) n A和 (75 8± 177) p A降至 (5 .4± 1.7)、(2 .2± 1.6 ) n A和 (335± 12 2 )、(137±10 0 ) p A。L ine10 μmol/ L 抑制 INa和 ICa- L的 I- V曲线并使后者的峰值电流电位略右移。结果表明 L ien有钠、L -型钙通道阻滞作用 。

芍药苷对大鼠心肌细胞L钙通道的阻断作用

目的 在单个大鼠心肌细胞上 ,研究芍药苷对L型钙通道的阻断作用。方法 采用全细胞膜片钳技术。结果 芍药苷浓度依赖性阻断ICa ,L,其IC50 为 387μmol·L- 1 。应用 40 0 μmol·L- 1 芍药苷后 ,ICa,L最大电流幅度下降 51 % ,但I U曲线的形态和反转电位没有变化 ,激活曲线也没有明显的改变 ;失活曲线向较负电压的方向偏移约 8 3mV ,通道从失活中恢复的时间明显延长 ,由给药前的 (96± 1 7)ms增至 (1 85± 2 8)ms ;芍药苷的阻断作用没有显示出频率依赖性。结论 芍药苷对心肌细胞ICa 。