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.     

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)。     

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.     

Taurine modulates I(Kr) but I(Ks) in guinea-pig ventricular cardiomyocytes

1. Effects of taurine on the delayed rectifier K+ current (I(K)) in isolated guinea-pig ventricular cardiomyocytes were examined at different intracellular Ca2+ concentration ([Ca2+]i), using whole-cell voltage and current clamp techniques. Experiments were performed at 36 degrees C. 2. Addition of taurine (10-20 mM) decreased the action potential duration (APD) at pCa 8, but increased the APD at pCa 6. Taurine (20 mM) enhanced I(K) at 70 mV by 22.4 +/- 3.1% (n = 6, P < 0.01) at pCa 8, whereas taurine inhibited the I(K) by 27.1 +/- 2.7% (n = 6, P < 0.01) at pCa 6. These responses behaved in a concentration-dependent manner. 3. The I(K) is composed of the rapid and slow components (I(Kr) and I(Ks)). When [Ca2+]i was pCa 6, taurine at 20 mM reduced the tail current of I(Kr) at 70 mV by 16.5 +/- 2.7% (n = 5, P < 0.05) and that of I(Ks) at 70 mV by 27.1 +/- 2.8% (n = 6, P < 0.01). In contrast, at pCa 8, the tail currents of I(Kr) and I(Ks) at 70 mV were enhanced by 13.4 +/- 3.2% (n = 7, P < 0.05) and by 22.4 +/- 3.1% (n = 7, P < 0.01), respectively. The voltages of half-maximum activation (V1/2) for I(Kr) and I(Ks) were not modified by taurine. 4. Addition of E-4031 (5 microM) to taurine had a complete blockade of the tail current of I(Kr), but not I(Ks). The remained tail current (I(Ks)) in the presence of E-4031 (5 microM) was not affected by taurine (20 mM), but was blocked by 293B (30 microM). 5. These results indicate that taurine modulates I(Kr) but not I(Ks), depending on [Ca2+]i, resulting in regulation of the APD.     

银杏酮酯对缺血豚鼠心室肌细胞Ⅰ_(Ca-L)和游离钙的影响

目的观察银杏酮酯GBE50对模拟缺血游离豚鼠心室肌细胞L型钙电流和游离钙浓度的影响,探讨GBE50抗心肌缺血的作用机制。方法应用单酶酶解法分离游离单个豚鼠心室肌细胞,采用膜片钳全细胞记录心室肌细胞L型钙电流,通过激光共聚焦显微镜扫描测定细胞内游离钙浓度的动态变化。结果缺血抑制豚鼠心室肌细胞的ICa-L(n=9,P<0.01),使豚鼠心室肌细胞内游离钙增加(n=10,P<0.01),而50mg·mL-1GBE50减轻缺血对ICa-L的抑制效应(n=6,P>0.05),减少缺血后心室肌细胞内游离钙浓度的增加(n=10,P>0.05)。结论GBE50可减轻心肌缺血区域与非缺血区域电生理的异质性,维持缺血后豚鼠心肌细胞电生理的稳定性,并减轻缺血后心肌细胞内钙超载介导的心肌损伤。     

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.     

Perforated patch recording of L-type calcium current with beta-escin in guinea pig ventricular myocytes

AIM: To establish a perforated patch recording (PPR) mode with beta-escin and compare L-type calcium current (I(Ca,L)) recorded under PPR and normal whole-cell recording (WCR) condition in isolated guinea-pig ventricular myocytes. METHODS: Single myocytes were dissociated by enzymatic dissociation method. beta-escin was added to the pipette solution to perforate the cell membrane and obtain PPR mode. I(Ca,L) was recorded using PPR and WCR techniques. RESULTS: beta-Escin 20, 25, and 30 micromol/L could permeabilize the cell membrane and obtain PPR mode. With beta-escin 25 micromol/L, the success rate was highest (16/17, 94 %) and the time required for permibilization was 2-15 (8+/-4) min. Run-down of I(Ca,L) was considerably slower in PPR than in WCR condition. The amplitude of I(Ca,L) was decreased by 36 % at 20 min after the formation of WCR, while it was slowly decreased by 8 % at 30 min after the formation of PPR. The current-voltage relation (I-V) curves, activation and inactivation curves of I(Ca,L) were not significantly different between WCR and PPR. The inactivation rate of ICa,L was slower in PPR than in WCR, the faster inactivation time constant (tau(f)) was longer in PPR than in WCR at membrane potentials of -20 mV -- +10 mV (n=6, P<0.05), and the slower time constant (tau(s)) was also longer in PPR than in WCR at membrane potentials of -10 mV to +10 mV (n=6, P<0.05). There was no significant difference between the activation rate in WCR and PPR. CONCLUSION: Using beta-escin 25 micromol/L can easily obtain stable PPR in isolated guinea-pig ventricular myocytes, and this method is useful in dealing with channels, which show run-down under normal WCR such as L-type Ca channel.     

环维黄杨星D对分离大鼠心室肌细胞内Ca2+和L型钙电流的影响

目的研究环维黄杨星D（CD）对大鼠心室肌细胞内Ca²⁺动员和L型钙电流(I_{Ca-L/sub>)的影响。方法采用全细胞膜片钳和激光扫描共聚焦显微术研究CD对心肌细胞ICa-L/sub>以及氯化钾、咖啡因诱发心肌细胞内Ca²⁺动员的影响。结果CD浓度依赖性抑制ICa-L/sub>。指令电压为10 mV时，1和10 μmol·L^-1 CD分别使ICa-L/sub>电流密度从（-9.9±1.8）pA/pF降至（-6.4±1.4）pA/pF和（-4.2±0.6）pA/pF。共聚焦实验显示1和10 μmol·L^-1 CD不影响静息心肌细胞［Ca²⁺］i?/sub>，对氯化钾诱发［Ca²⁺］i?/sub>升高水平无明显抑制作用；咖啡因引起的细胞内Ca²⁺动员可被CD进一步增强。结论CD浓度依赖性抑制大鼠心室肌细胞ICa-L/sub>，并有促进咖啡因诱发心肌细胞内Ca²⁺释放的作用。}     

Effects of Ginkgolide B on action potential and calcium, potassium current in guinea pig ventricular myocytes

INTRODUCTION Ginkgo biloba extract (GbE) is extracted fromthe leaves of Ginkgo biloba. GbE is a multicomponentdrug with a polyvalent action. In Germany and France,such extracts were used effectively to treat cerebraldysfunction and peripheral circulatory disturbances[1].The results of clinical trails support new indications forGbE in the treatment of cardiovascular disease, par-ticularly in the prevention of ischemic heart syndromes[2].The primary active constituents of GbE incl…     

Muscarinic cholinergic regulation of L-type calcium channel in heart of embryonic mice at different developmental stages

AIM: To investigate the muscarinic regulation of L-type calcium current (ICa_L) during development. METHODS: The whole cell patch-clamp technique was used to record ICa_L in mice embryonic cardiomyocytes at different stages (the early developmental stage, EDS; the intermediate developmental stage, IDS; and the late developmental stage, LDS). Carbachol (CCh) was used to stimulate M-receptor in the embryonic cardiomyocytes of mice. RESULTS: The expression of 7Ca-L density did not change in different developmental stages (P>0.05). There was no difference in the sensitivity of ICa_L to CCh during development (P>0.05). This inhibitory action of CCh was mediated by inhibition of cyclic AMP since 8-bromo-cAMP completely reversed the muscarinic inhibitory action. IBMX, a non-selective inhibitor of phosphodiesterase (PDE), reversed the inhibitory action of M-receptor on 7Ca-L current by 71.2 %±9.2 % (n=8) and 11.3 %±2.5 % (n=9) in EDS and LDS respectively. However forskolin, an agonist of adenylyl cyclase (AC),     

钙通道阻塞剂对大鼠肝细胞钙释放激活的钙电流的影响

目的 研究钙通道拮抗剂对大鼠肝细胞钙释放激活的钙电流（ＩＣＲＡＣ）的影响。方法 应用全细胞膜片箝技术。结果：ＩＣＲＡＣ的电流峰值是（－０．４１±０．０９）ｎＡ（ｎ＝１５）反转电位约为０ｍＶ。维拉帕米（Ｖｅｒ）地尔硫Ｚｕｏ（Ｄｉｌ）和硝苯地平（Ｎｉｆ）显著降低ＩＣＲＡＣ不影响它的反转电位,Ｖｅｒ５μｍｏｌ．Ｌ＾－１的抑制率是４０％±１２％（ｎ＝３）,Ｖｅｒ５０μｍｏｌ．Ｌ＾－１使ＩＣＲＡＣ的幅值从（     

大黄素对豚鼠单个心室肌细胞胞浆游离钙浓度及L-型钙电流的影响

目的研究大黄素(emodin)对豚鼠心室肌细胞钙信号的影响。方法酶解法分离豚鼠单个心室肌细胞,应用激光扫描共聚焦显微镜联合全细胞膜片钳技术测量豚鼠心室肌细胞钙信号的变化。结果在静息状态下,1～100 μmol·L^-1大黄素对［Ca²⁺］i均无影响;对60 mmol·L^-1 KCl诱导的外钙内流引起的胞浆钙升高有不同的影响,1 μmol·L^-1表现为促进作用;10 μmol·L^-1无作用;100 μmol·L^-1则表现为抑制作用。膜片钳研究结果表明,1 μmol·L^-1大黄素可明显促进L-型钙电流,10 μmol·L^-1对L-型钙电流无影响;100 μmol·L^-1明显抑制L-型钙电流。结论大黄素对心肌细胞内钙及L-型钙电流具有双向调节作用。     

Sulfur dioxide derivatives depress L-type calcium channel in rat cardiomyocytes

1. Sulfur dioxide (SO(2) ) has recently been found to have various biological effects on the cardiovascular system. The present study was designed to explore the effects of SO(2) derivatives on the L-type calcium current (I (Ca, L) ) in isolated rat ventricular cardiomyocytes. 2. A Langendorf system was used to dissociate single ventricular cells. SO(2) derivatives from 5 to 1000 μmol/L were incubated with cardiomyocytes. The whole-cell patch-clamp technique was used to record I (Ca, L) . The effect of SO(2) derivatives on intracellular calcium concentration ([Ca(2+) ](i) ) was detected by confocal microscopy. 3. Concentrations of 5 or 10 μmol/L SO(2) derivatives could not change I (Ca, L) evoked by a single pulse from -40 to 0 mV for 200 ms in rat ventricular cardiomyocytes; however, 50, 100, 500 or 1000 μmol/L SO(2) derivatives could depress the peak amplitudes of calcium currents in 6 min, and the I (Ca, L) was attenuated by 13.19%, 16.59%, 21.23% and 24.72%, respectively, as compared with corresponding controls (P < 0.05). The 50, 100, 500 or 1000 μmol/L SO(2) derivatives also depressed the peak I-V curves, without altering the reversal potential and the voltage dependence of the peak I (Ca, L) . Therefore, 1000 μmol/L SO(2) derivatives could reduce [Ca(2+) ](i) in cardiomyocytes. 4. The results of the present study suggest that SO(2) derivatives can depress I (Ca, L) in cardiomyocytes, which might have a protective effect in cardiovascular diseases.     

Effects of the class III antiarrhythmic agent dofetilide (UK-68,798) on L-type calcium current from rabbit ventricular myocytes.

The methanesulphonanilide agent dofetilide (UK-68,798) exerts Class III antiarrhythmic effects by inhibiting the cardiac rapid delayed rectifier potassium current (I(Kr)) encoded by HERG. The aim of the present study was to determine whether dofetilide also exhibits Class IV (L-type calcium-channel blocking) effects. L-type calcium current (I(Ca,L)) was measured from rabbit isolated ventricular myocytes, using the whole-cell patch-clamp technique under selective recording conditions. Positive control experiments demonstrated inhibition of I(Ca,L) elicited by pulses to + 10 mV by both nifedipine and externally applied Ni2+ ions. Three concentrations of dofetilide were tested: 100 nM, 1 microM and 10 microM. I(Ca,L) magnitude was not significantly reduced by any of the concentrations tested (P > 0.05; n = minimum of seven cells per drug concentration). The inactivation time-course of I(Ca,L) was also unaffected by 10 microM dofetilide. Heterologously expressed HERG current (I(HERG)) recorded from Chinese Hamster Ovary cells was extensively inhibited by 100 nm and 1 microM dofetilide, with inhibition at 1 microM not significantly different from 100% (P > 0.1). It is concluded that dofetilide produced no I(Ca,L) blocking effects at concentrations up to and exceeding that required for maximal I(HERG) inhibition. The findings support the notion that dofetilide is a highly selective Class III antiarrhythmic agent, devoid of Class IV antiarrhythmic activity.     

Effects of phenylalkylamines and benzothiazepines on Ca(v)1.3-mediated Ca2+ currents in neonatal mouse inner hair cells

Calcium currents (I(Ca)) in inner hair cells (IHCs) are carried by the Ca(v)1.3 subtype of L-type calcium channels. They play an important role in synaptic transmission of sound-evoked mechanical stimuli. L-type calcium channels are targets of the organic blocker classes dihydropyridines, phenylalkylamines and benzothiazepines. Previously a low sensitivity of the Ca(v)1.3 subtype towards dihydropyridines has been demonstrated. Therefore, this study evaluates the effect of two phenylalkylamines (verapamil and gallopamil) and the benzothiazepine diltiazem on I(Ca) through Ca(v)1.3 channels in mouse IHCs. Whole-cell I(Ca) was measured using the patch-clamp technique in mouse IHCs aged postnatal day 3-7 with 5 mM calcium as a charge carrier. The phenylalkylamines verapamil and gallopamil and the benzothiazepine diltiazem inhibited I(Ca) in IHCs in a concentration-dependent manner. This block was largely reversible. Dose-response curves revealed IC(50) values of 199+/-19 microM for verapamil, 466+/-151 microM for gallopamil and 326+/-67 microM for diltiazem. The inhibition of peak I(Ca) by phenylalkylamines and benzothiazepines was voltage-independent. Verapamil (300 microM) enhanced current inactivation from -20 to +20 mV while diltiazem (300 microM) did so only at very depolarised potentials (+20 mV). In conclusion, the concentrations of phenylalkylamines and benzothiazepine necessary to inhibit 50% of I(Ca) in IHCs were one order larger compared to concentrations which inhibited I(Ca) through Ca(v)1.2 channels in native cells or expression systems. However, inhibitory concentrations were in the same range as those required for block of I(Ca) in turtle hair cells.     

蜂毒肽增强豚鼠心室肌细胞Na~ -Ca~(2 )交换电流(英文)

目的:研究蜂毒肽使心肌细胞钙超负荷的机制。方法:全细胞膜片箝记录。结果:蜂毒肽0.05,0.1μmol/L促进I_(Na)峰值(nA)从-2.1±0.8分别增加到-3.2±1.0(n=7,P<0.05)和-3.7±1.5(n=7,P<0.05)。蜂毒肽0.05,0.1,0.2μmol/L对I_(Ca)无显著性作用,但在箝制电位为 50mV时,促进I_(Na-Ca)(pA)从53±21分别增加到427±256(n=5,P<0.05),349±147(n=5,P<0.01)和320±97(n=5,P<0.05)。结论:蜂毒肽使心肌细胞内钙增加主要是由于促进Na~ -Ca~(2 )交换电流而不是L-型钙电流。     

Alteration of cytosolic calcium levels in PC12 cells by potassium cyanide

The effect of KCN on cytosolic Ca2+ levels was measured in PC12 cells using Quin II/AM, a fluorometric calcium indicator. The resting cytosolic Ca2+ concentration, 115.0 +/- 4.9 nm, increased gradually and steadily over a 30-min time period following addition of 10(-4), 10(-3), or 10(-2)M KCN to the cells. After 15 min, 10(-3) and 10(-2)M KCN produced a three- and sixfold increase in the cytosolic Ca2+ concentration, respectively. In K+-depolarized cells, KCN induced a more rapid rise of intracellular calcium than in cells treated with KCN or KCI alone. KCN and/or K+-induced accumulation of cytosolic Ca2+ was blocked when the cells were pretreated with 10(-5)M diltiazem (a calcium channel blocker). These results demonstrate in a cell model that cyanide induces an accumulation of cytosolic Ca2+ and this additional cytosolic Ca2+ load appears to originate primarily from the extracellular compartment. This study supports previous reports implicating calcium as an intracellular mediator of cyanide toxicity.     

Cocaine activates calcium/calmodulin kinase II and causes cardiomyocyte hypertrophy

Cardiac hypertrophy occurs in as many as 47% of normotensive individuals who chronically use cocaine. We investigated the effects of cocaine, in concentrations commonly found in chronic cocaine users, on calcium/calmodulin kinase (CaMK), and whether cocaine can activate CaMK, increase cardiac myocyte protein expression, and cause cardiac hypertrophy in this manner. In series I to III, 0 (control) or cocaine in concentrations of 10 to 10 mol/L was added to cultured adult rat cardiac ventricular myocytes to determine by Western blots and by P incorporation the optimal treatment time and the optimal dose for CaMK activation. In series I, cocaine, 10 mol/L, increased myocyte CaMKII translocation from myocyte soluble to particulate fractions by > or =73 +/- 9% (P < 0.01) in comparison with controls but did not cause the translocation of CaMKI or CaMKIV. In series II and III, cocaine treatment of myocytes for 15 minutes increased maximal CaMKII activity by 86.5 +/- 13.3% (P < 0.001) and a cocaine dose of 5 x 10 mol/L increased CaMKII activity by 169.5 +/- 18.1% (P < 0.001). In series IV we measured by silver staining beta-myosin heavy chain protein (beta-MHC) expression in myocytes before and after cocaine and also CaMK inhibition with KN-62 (1-[N,O-bis-(5-isoquinolinesulfonyl)-N-methyl-L-tyrosyl]-4-phenylpiperazine). In these experiments, cocaine, 5x10 mol/L, increased myocyte protein concentration by 29.2 +/- 2.8%, and beta-MHC by 93.2 +/- 8.8% (P < 0.001). In series V and VI, cocaine effects on calcium currents (ICa) and intracellular Ca ([Ca]i) were determined before and after CaMK inhibition with KN-62 in rat myocytes. Cocaine, 10 mol/L, enhanced ICa peak amplitude in a voltage-dependent manner (by 173.9 +/- 14.9% at -20 mV and by 38.4 +/- 6.9% at 0 mV P < 0.01). Cocaine, 10 to 10 mol/L, in series VI promoted Ca transients from myocyte sarcoplasmic reticulum and increased [Ca]i to 607 +/- 141 x 10 mol/L (P < 0.05). KN-62 decreased cocaine-induced myocyte protein expression by 76.6%, and beta-MHC by 66.2% (P < 0.01) and significantly decreased cocaine-induced Ca transients and [Ca]i. We conclude that CaMKII activation is an important mechanism whereby cocaine can cause myocyte hypertrophy.     

Suppression of calcium current in a snail neurone by eperisone and its analogues

The effects of eperisone, tolperisone and isoperisone on the calcium current (ICa) were studied in an identified neurone of Achatina fulica under voltage clamping. At a holding voltage of -50 mV, these drugs inhibited ICa dose dependently without affecting activation time. Eperisone (IC50 = 0.348 mM) and isoperisone (0.226 mM) were significantly more effective than tolperisone (1.089 mM). Eperisone binds competitively with Ca2+ to the Ca2+ channels, based on its effects seen with various extracellular Ca2+ concentrations. The three drugs shifted the steady state inactivation curves in the hyperpolarizing direction. The mean dissociation constants for inactivated Ca2+ channels were calculated to be 0.070 mM (eperisone), 0.162 mM (tolperisone) and 0.014 mM (isoperisone). These values were much lower than their IC50 at Vh of -50 mV, which are reflected as the dissociation constants for resting Ca2+ channels. High frequency stimulation did not potentiate ICa suppression, suggesting that the drugs hardly bind to activated Ca2+ channels. These findings indicate that the selectivities of the Ca2+ channels to the drugs are in the order of their inactivated, resting and open states.     

Regulation of the calcium channel alpha(1G) subunit by divalent cations and organic blockers

The pharmacological properties of the expressed murine T-type alpha(1G) channel were characterized using the whole cell patch clamp configuration. Ba(2+) or Ca(2+) were used as charge carriers. Both I(Ba) and I(Ca) were blocked by Ni(2+) and Cd(2+) with IC(50) values of 0.47+/-0.04 and 1.13+/-0.06 mM (Ni(2+)) and 162+/-13 and 658+/-23 microM (Cd(2+)), respectively. Ni(2+), but not Cd(2+), modified the gating of channel activation. Ni(2+) consistently accelerated channel deactivation while Cd(2+) had a similar effect only on I(Ca). The alpha(1G) channel was potently blocked by mibefradil in a dose- and voltage-dependent manner. I(Ba) was moderately blocked by phenytoin (IC(50) 73.9+/-1.9 microM) and was resistant to the block by valproate. Also 3 mM ethosuximide blocked 20 and 35% of the I(Ba) at a HP of -100 and -60 mV, respectively, while 5 mM amiloride inhibited I(Ba) by 38% and significantly slowed current activation. The alpha(1G) channel was not affected by 10 microM tetrodotoxin. Both 1 microM (+)isradipine and 10 microM nifedipine inhibited 18 and 14% of I(Ba) amplitude at a HP of -100 mV, and 23% and 29% of I(Ba) amplitude at a HP of -60 mV, respectively. The alpha(1G) current was minimally activated by 1 microM Bay K 8644.