急性心肌梗死对心室肌细胞钾电流的影响

目的 :研究急性心肌梗死 （AMI）心室肌细胞瞬时外向钾电流 （Ito）和内向整流性钾电流 （IK1 ）的变化。方法 :采用结扎兔冠状动脉左前降支的方法建立 AMI动物模型 ,应用膜片钳全细胞记录方法 ,记录比较 AMI后 1周心外膜梗死区心肌细胞 Ito和 IK1 的变化。结果 :心梗组 Ito明显下降 ,I- V曲线明显下移。指令电位为 +60 m V时 ,Ito在心梗组为 1.0 8± 0 .2 4n A（n=12 ） ,与对照组 （2 .0 9± 0 .3 9n A ,n=16）相比 ,显著下降 ,P<0 .0 1;心梗组 IK1 与对照组比较 ,明显下降 ,特别在超极化时。指令电位为 - 12 0 m V时 ,心梗组 IK1 为 3 .0 1± 0 .49n A （n=11） ,对照组为 4.12±0 .5 1n A（n=10 ,P<0 .0 5 ）。结论 :AMI可引起心室肌细胞 Ito和 IK1 的下降 ,从而导致动作电位平台期延长、复极异常 ,这可能是导致 AMI后出现折返性室性心律失常的原因     

增强型绿色荧光蛋白转染小鼠心脏后瞬时外向钾电流及钠钙交换电流的变化

目的探讨绿色荧光蛋白(GFP)转染对心脏瞬时外向钾电流(Ito)及钠钙交换电流(INCX)的影响。方法20只雄性小鼠等量随机分为对照组和增强型GFP(EGFP)组。EGFP组小鼠采用8点注射法均匀注射100μl腺病毒于左室游离壁上,对照组注射等量无菌生理盐水。一周后分离单个心室肌细胞,用膜片钳记录Ito及INCX。结果与对照组相比,EGFP组几乎所有测定电压下,Ito电流密度显著减小[如+60 mV时为8.40±1.55 pA/pF(n=9)vs 36.77±8.12 pA/pF(n=11),P<0.05]。INCX的前向模式不因转染EGFP变化[如-80 mV时为-0.35±0.05 pA/pF(n=8)vs-0.42±0.08 pA/pF(n=10),P>0.05],但反向模式电流显著增大[如+80 mV时为1.47±0.10 pA/pF(n=8)vs 0.72±0.05 pA/pF(n=10),P<0.05]。结论 EGFP转染可使心脏Ito显著减小,而INCX仅反向模式电流增大,其综合效应可能导致细胞内钙增加。     

咪达普利对陈旧性心肌梗死非梗死区心肌跨室壁复极离散度及短暂外向钾电流的影响

目的 探讨咪达普利对陈旧性心肌梗死非梗死区心肌跨室壁复极离散度（TDR）以及短暂外向钾电流（Ito）的影响。方法24只兔随机分为3组,两组结扎左冠状动脉回旋支制成心肌梗死模型,手术后1周1组给予咪达普利 0.625mg·kg-1·d-1口服（咪达普利组）,另1组则给予安慰剂口服（陈旧性心肌梗死组）;第3组开胸但不结扎冠状动脉也给予安慰剂口服（假手术组）。3个月后酶解分离得到左心室壁远离梗死中心区的3层心肌单细胞（心外膜下心肌细胞、中层心肌细胞和心内膜下心肌细胞）,用膜片钳技术研究跨室壁复极离散度（TDR）以及3层心肌细胞的短暂外向钾电流（Ito）的改变。结果 心肌梗死后3个月,非梗死区的心肌细胞发生了肥厚和重构,3层心肌细胞的动作电位时限（APD）明显延长,其中心内膜下心肌细胞的APD明显短于心外膜下心肌细胞和中层心肌细胞（P<0.01）,与假手术组对比呈相反的跨室壁离散。陈旧性心肌梗死TDR也明显增加,但TDR在咪达普利组和假手术组间差异不明显。陈旧性心肌梗死3层心肌细胞的Ito密度均降低,以心外膜下心肌细胞和中层心肌细胞较明显（P<0.05）,咪达普利组和假手术组相比,Ito密度无明显改变（P>0.05）。结论陈旧性心肌梗死远离梗死中心区的左心室心肌细胞发生代偿性肥厚,APD延长,TDR增加,3层心肌细     

Mathematical simulations of the effects of altered AMP-kinase activity on I and the action potential in rat ventricle

Introduction: Alterations in the activity of a so‐called “metabolic switch” enzyme, adenosine monophosphate‐activated protein kinase (AMP kinase), in mammalian heart contribute to the conduction abnormalities and rhythm disturbances in the settings of Wolff‐Parkinson‐White syndrome and ventricular pre‐excitation. A recent study by Light et al. has shown that augmented AMP kinase activity can alter the biophysical properties of mammalian cardiac sodium currents. These experiments involved an electrophysiological analysis following heterologous expression of human Na_v1.5 in tsA201 cells. Constitutive activation of AMP kinase followed by co‐transfection caused: (i) a hyperpolarizing shift in the activation curve for I_Na, (ii) a small change in the voltage dependence of steady‐state inactivation, and (iii) a significant slowing in the rate of inactivation of I_Na. Methods and Results: We have attempted to simulate these results using our mathematical model of the membrane action potential of the adult rat ventricular myocyte. The changes in I_Na produced by AMP kinase activation and/or overexpression can be reconstructed mathematically by altering two rate constants in a Markovian model that governs the I_Na kinetics. Simulated macroscopic I_Na records in which a fraction (10–100%) of the Na⁺ channels had the appropriate rate constants for two state‐dependent transitions increased by a factor of 100‐fold exhibited: (i) slowed inactivation, (ii) a shift in steady‐state activation to more hyperpolarized membrane potentials, and (iii) a very small change in the voltage dependence of steady‐state inactivation. Summary: Thus, straightforward modifications of a previously published kinetic scheme for the time and voltage dependence of mammalian heart I_Na, when incorporated into a mathematical model for the rat ventricular action potential can reproduce the main features of these AMP kinase‐induced modifications in I_Na in mammalian ventricle. Ongoing mathematical simulations are directed toward developing formulations that mimic the molecular mechanisms for the AMP kinase effects, e.g., changes in the kinetics of I_Na resulting from selective phosphorylation/dephosphorylation of sites on the alpha or beta subunits which comprise human Na_v1.5. Thereafter, incorporation of these changes into a mathematical model for the action potential of the human ventricular myocyte is planned.     

氧化苯胂对大鼠心室肌细胞L型Ca2+电流的影响

目的 :探讨氧化苯胂 （PAO） ,一种膜可通透的酪氨酸磷酸酶抑制剂 ,对大鼠心室肌细胞 L型 Ca2 +电流 （ICa,L）的影响。方法 :采用全细胞膜片钳技术记录大鼠心室肌细胞 ICa,L。结果 :1PAO对基础 ICa,L及β-肾上腺素受体激动剂异丙肾上腺素 （Iso）激发的 ICa,L有抑制作用 ;2 PAO对腺苷酸环化酶激动剂 forskolin激发的 ICa,L亦有抑制作用 ;3电极内液加入 1.5 mm ol/ L矾酸钠不能消除 PAO的作用 ;4PAO对 ICa,L的抑制作用可被二硫代苏糖醇反转。结论 :PAO抑制 ICa,L的作用与 c AMP- PKA-磷酸化途径和酪氨酸磷酸酶无关 ,可能与其使 L 型 Ca2 +通道蛋白上巯基氧化有关。     

2-iodomelatonin prevents apoptosis of cerebellar granule neurons via inhibition of A-type transient outward K+ currents

Compelling evidence indicates that excessive K+ efflux and intracellular K+ depletion are key early steps in apoptosis. Previously, we reported that apoptosis of cerebellar granular neurons induced by incubation under low K+ (5 mM) conditions was associated with an increase in delayed rectifier outward K+ current (IK) amplitude and caspase-3 activity. Moreover, the melatonin receptor antagonist 4P-PDOT abrogated the effects of 2-iodomelatonin on IK augmentation, caspase-3 activity and apoptosis. Here, we show that incubation under low K+/serum-free conditions for 6 hr led to a dramatic increase in the A-type transient outward K+ current (IA) (a 27% increase; n=31); in addition, fluorescence staining showed that under these conditions, cell viability decreased by 30% compared with the control. Treatment with 2-iodomelatonin inhibited the IA amplitude recorded from control and apoptotic cells in a concentration-dependent manner and modified the IA channel activation kinetics of cells under control conditions. Moreover, 2-iodomelatonin increased the viability of cell undergoing apoptosis. Interestingly, 4P-PDOT did not abrogate the effect of 2-iodomelatonin on IA augmentation under these conditions; in the presence of 4P-PDOT (100 microm), 2-iodomelatonin reduced the average IA by 41+/-4%, which was similar to the effect of 2-iodomelatonin alone. These results suggest that the neuroprotective effects of 2-idomelatonin are not only because of its antioxidant or receptor-activating properties, but rather that 2-iodomelatonin may inhibit IA channels by acting as a channel blocker.     

Melatonin receptor agonist 2-iodomelatonin prevents apoptosis of cerebellar granule neurons via K(+) current inhibition

Activation of K(+) current plays a critical role in the control of programmed cell death. In the present study, whole-cell patch-clamp recording, a caspase-3 activity assay, and flow cytometric analysis were used to examine the effects of the MT2 melatonin receptor agonist 2-iodomelatonin on the delayed-rectifier K(+) current (IK) and the prevention of apoptosis. It was found that apoptosis of cerebellar granular neurons induced by low-K(+) (5 mm) incubation was associated with an increase in IK amplitude and caspase-3 activity. After 6 hr of low-K(+) treatment, IK was increased by 45% (n = 86). Flow cytometry showed that the apoptosis rate increased by 333% compared with the control neurons. In addition, exposure of cultured granule cells to low K(+) also resulted in a significant activation of caspase-3, by 466%. 2-Iodomelatonin (10 microm in injection pipette) inhibited the IK amplitude recorded from control cells and from cells undergoing apoptosis. However, 2-iodomelatonin only modified the IK-channel activation kinetics of cells under both conditions. Furthermore, 2-iodomelatonin reduced the rate of apoptosis and caspase-3 activation, by 66 and 64%, respectively. The melatonin receptor antagonist, 4P-PDOT, abrogated the effect of 2-iodomelatonin on the IK augmentation, caspase-3 activity, and apoptosis. These results suggest that the neuroprotective effects of melatonin are not only because of its function as a powerful antioxidant, but also to its interactions with specific receptors. The effect of 2-iodomelatonin against apoptosis may be mediated by activating a melatonin receptor, which modulates IK channels and reduces K(+) efflux.     

Effects of Mibefradil, a T-Type Calcium Current Antagonist, on Electrophysiology of Purkinje Fibers that Survived in the Infarcted Canine Heart

INTRODUCTION: We studied the effects of mibefradil (MIB), a nondihydropyridine T-type Ca2+ channel antagonist, on T- and L-type Ca2+ (I(CaT), I(CaL)) currents in Purkinje myocytes dispersed from the subendocardium of the left ventricle of normal (NZPC) and 48-hour infarcted (IZPC) hearts. METHODS AND RESULTS: Currents were recorded with Cs+- and EGTA-rich pipettes and in Na+-K+-free external solutions to eliminate overlapping currents. In all cells, I(Ca) was reduced by MIB (0.1 to 10 microM). No change in the time course of decay of peak I(Ca) was noted. Average peak T/L ratio decreased in NZPCs but not IZPCs with 1 microM MIB. Steady-state availability of I(CaL) was altered with 1 microM MIB in both cell types (mean +/- SEM) (V0.5 = -22 +/- 4 mV for NZPC and -25 +/- 5 mV for IZPC before drug; -63 +/- 9 mV for NZPC and -67 +/- 6 mV for IZPC after drug; P < 0.05). For I(CaT), V0.5 (-50 +/- 3 mV for NZPC and -52 +/- 1 mV for IZPC before drug) shifted to -60 +/- 2 mV (NZPC) and -62 +/- 3 mV (IZPC) (P < 0.05) after drug. We also determined the effects of MIB on spontaneously beating Purkinje normal fibers and on depolarized abnormally automatic fibers from the infarcted heart using standard microelectrode techniques. When NZPC and IZPC fibers were superfused with [K+]o = 2.7 mM, MIB 3 microM and 10 microM had no effect on rate or the maximum diastolic potential, but action potential plateau shifted to more negative values, the slope of repolarization phase 3 decreased, and action potential duration increased. CONCLUSION: MIB blocks L- and T-type Ca2+ currents in Purkinje myocytes but lacks an effect on either normal or abnormal automaticity in Purkinje fibers.     

Canine Ventricular Myocyte β2-Adrenoceptors Are Not Functionally Coupled to L-Type Calcium Current

INTRODUCTION: To establish the functional coupling of beta adrenoceptor (betaAR) subtypes beta1AR and beta2AR to L-type calcium current (I(CaL)), we investigated the nonselective agonist isoproterenol (ISO) and the relatively selective beta2AR agonists zinterol (ZIN) and salbutamol (SAL) on I(CaL) in isolated canine ventricular myocytes in the presence and absence of CGP 20712A (CGP) and atenolol (AT), selective beta1AR antagonists, and ICI 118,551 (ICI) a selective beta2AR antagonist. METHODS AND RESULTS: Peak I(CaL) was determined using "patch type" microelectrodes and whole cell voltage clamp. ISO (0.5 microM) increased I(CaL) maximally 3.5 +/- 0.67 fold. ZIN (10.0 microM) and SAL (10.0 microM) increased I(CaL) maximally 1.5 +/- 0.2 fold (n = 5) and 1.4 +/- 0.1 fold (n = 5), respectively. These effects were fully inhibited by CGP (0.3 microM) and AT (1.0 microM), which are inhibitors of beta1AR, but not by ICI (0.1 microM), which is a beta2AR inhibitor. ZIN at relatively lower concentrations (< or = 0.1 microM) did not increase I(CaL). CGP (0.3 microM) but not AT and ICI inhibited I(CaL) in the absence of betaAR agonists. CGP inhibition of I(CaL) was absent in the presence of forskolin (1.0 microM), which increases cAMP levels and I(CaL) by directly stimulating the adenylate cyclase. These data indicate that none of the antagonists affect I(CaL) through an action downstream of betaAR. CONCLUSION: Beta-adrenergic agonists increase I(CaL) via beta1AR but not beta2AR in canine ventricular myocytes.     

Mechanisms for Depolarization by I-PalmitoyIcarnitine in Single Guinea Pig Ventricular Myocytes

I-PC Inhibits I_Na/K and I_K1 in Heart. introduction: The changes of the resting potential (RP) and of the current-voltage (I-V) relationship induced by l-palmitoylcarnitine (I-PC) in the presence of the I_K1 blocker, cesium, or in the presence of the I_Na/K blocker, ouabain, were tested in guinea pig ventricular myocytes to ascertain the relative contributions of I_K1 and I_Na/k suppression to the membrane depolarization caused by this amphiphile. Methods and Results: Ramp voltages were applied to myocytes with the whole cell, patch clamp technique. 1-PC (10 μM) produced additional membrane depolarization in the presence of either 10 mM Cs⁺ or 30 μM ouabain. In the presence of Cs⁺ 1-PC, like 3 μM ouabain, shifted current inward at potentials negative to -20 mV as a result of I_Na/K blockade. In the presence of 30 μM ouabain, 1-PC, like Cs⁺, shifted current inward at potentials between -27 and -88 mV and outward at potentials negative to -88 mV. This is attributed to I_K1 block because the current was inwardly rectifying, with a reversal potential near E_K. When I-PC or ouabain inhibited I_Na/K, the presence of an Ni²⁺-sensitive component attributed to I_Na/ca distorted the membrane I-V relationship, particularly in the presence of Cs⁺. The relative contributions of I_K1 and I_Na/K block by 1-PC were voltage dependent. At the RP, 1-PC produced a greater block of I_Na/K than of I_K1. Conclusion: I-PC depolarizes the resting membrane by inhibiting both I_K1 and I_Na/K. It is concluded that suppression of I_Na/K by I-PC predominates over block of IK, to depolarize the membrane at the RP.     

Chronic heart failure slows late sodium current in human and canine ventricular myocytes: implications for repolarization variability

BACKGROUND: Late Na(+) current (I(NaL)) in human and dog hearts has been implicated in abnormal repolarization associated with heart failure (HF). HF slows inactivation gating of late Na(+) channels, which could contribute to these abnormalities. AIMS: To test how altered gating affects I(NaL) time course, Na(+) influx, and action potential (AP) repolarization. METHODS: I(NaL) and AP were measured by patch clamp in left ventricular cardiomyocytes from normal and failing hearts of humans and dogs. Canine HF was induced by coronary microembolization. RESULTS: I(NaL) decay was slower and I(NaL) density was greater in failing hearts than in normal hearts at 24 degrees C (human hearts: tau=659+/-16 vs. 529+/-21 ms; n=16 and 4 hearts, respectively; mean+/-SEM; p<0.002; dog hearts: 561+/-13 vs. 420+/-17 ms; and 0.307+/-0.014 vs. 0.235+/-0.019 pA/pF; n=25 and 14 hearts, respectively; p<0.005) and at 37 degrees C this difference tended to increase. These I(NaL) changes resulted in much greater (53.6%) total Na(+) influx in failing cardiomyocytes. I(NaL) was sensitive to cadmium but not to cyanide and exhibited low sensitivity to saxitoxin (IC(50)=62 nM) or tetrodotoxin (IC(50)=1.2 muM), tested in dogs. A 50% I(NaL) inhibition by toxins or passing current opposite to I(NaL), decreased beat-to-beat AP variability and eliminated early afterdepolarizations in failing cardiomyocytes. CONCLUSIONS: Chronic HF leads to larger and slower I(NaL) generated mainly by the cardiac-type Na(+) channel isoform, contributing to larger Na(+) influx and AP duration variability. Interventions designed to reduce/normalize I(NaL) represent a potential cardioprotective mechanism in HF via reduction of related Na(+) and Ca(2+) overload and improvement of repolarization.     

Bepridil对豚鼠心室肌细胞动作电位时程和跨膜离子流的作用

为观察bepridi1对豚鼠单心室肌细胞动作电位时程 (APD)及动作电位形成过程中主要离子流的作用 ,探讨其诱发长QT间期及多形性室性心动过速的电生理机制。采用Nystatin 破膜法研究bepridil对豚鼠单心室肌细胞APD的作用 ,常规全细胞方法研究其对主要跨膜离子流的作用。结果 :在 5Hz剌激频率时 ,0 .1μmol/Lbepridil使APD明显延长 ,APD90 平均延长 18.0l%( 6 2 .40± 7.6 5msvs 5 2 .88± 5 .90ms,P <0 .0 5 )。当bepridil在细胞外液中的浓度增至1或 3μmol/L时 ,APD恢复到用药前水平 ;但当药物浓度进一步提高到 10 μmol/L时 ,APD明显缩短 ,动作电位幅度下降 ,这一作用随着药物浓度的升高而加强。在持续 2 5 0ms和 10 0 0ms至不同膜电位的去极化的实验中 ,bepridil能明显降低延迟整流钾电流 (IK)的尾电流和稳态电流 ,抑制作用呈浓度依赖性。在 3 0 0 0ms、+6 0mV去极化及IK的快成分 (Ikr)被E 40 31完全阻断时 ,bepridil对IK 的慢成分 (Iks)亦具有抑制作用 ,但两种情况下的半抑制浓度 (IC50 )不同 :3 0 0 0ms,+6 0mV去极化bepridil对IK 的IC50 为 1.6 2 μmol/L ,约为在 +2 0mV、10 0 0ms去极化时对IK 尾电流IC50 ( 0 .12 μmol/L)的 13.5倍。在 1Hz频率去极化时 ,该药对钠电流 (INa)和钙电流 (ICa)也具有浓     

Are We Lost in the Labyrinth of the Sinoatrial Node Pacemaker Mechanism?

Despite extensive electrophysiologic studies performed to date, the ionic mechanisms of sinoatrial node pacemaker activity are unclear. This article highlights three recent topics associated with this issue: (1) sustained inward current (Ist)); (2) the role of Ca2+ release from the sarcoplasmic reticulum; and (3) the role of L-type Ca2+ current (I(Ca,L)). New observations on these topics seem to make the scenario of the pacemaker mechanism increasingly complex. However, such complexity and diversity of ionic events and their orchestration may be important for the sinoatrial node to perform its robust pacemaking activity under a variety of pathophysiologic circumstances.     

迷走神经和肺静脉刺激对心房肌动作电位和乙酰胆碱激活钾电流的影响

目的研究迷走神经和肺静脉快速刺激对心房肌动作电位和乙酰胆碱激活钾电流的影响。方法24只犬随机分为3组,每组8只犬。对照组：采用20Hz频率和0．2ms波宽刺激迷走神经,观察诱发心房颤动（房颤）情况。左上肺静脉（LSPV）刺激组：快速刺激LSPV4h,观察刺激前后左有心房和LSPV动作电位时限（APD）的变化,随后行迷走神经刺激,观察诱发房颤情况。迷走神经干预组：先采用5Hz频率、0．2ms波宽和5～10V电压刺激迷走神经30min,然后快速刺激LSPV4h,观察刺激前后APD的变化,冉迷走神经刺激观察诱发房颤情况。所有犬在电生理检测后开胸取心脏,分离LSPV和左右心房肌细胞,采用膜片钳技术观察乙酰胆碱激活钾电流（IK,ACh）变化。结果LSPV刺激组,APD。明显缩短,动作电位时限高散度（dAPD90）明显增加[（5±3）msVS（14±5）ms,P〈0．05]。迷走神经干预组,APD。无明显变化,但APD90-d明显增加[（6±3）mvs vs（12±5）ms,P〈0．05]。与对照组相比,LSPV刺激组细胞Ik、ACh明显增加,但对照组与迷走神经干预组相比,IK．ACh差异无统计学意义。结论APD缩短是胆碱能房颤诱发的基础,肺静脉快速刺激可增加IK．ACh密度,快速刺激前行迷走神经能阻止电重构的发生。     

氯沙坦对自发性高血压大鼠心肌细胞钙电流影响的分子机制

目的:探讨自发性高血压大鼠(SHR)心肌细胞L型钙电流(ICa-L)和L型钙通道a1C亚基(CaL.α1C)信使核糖核酸(mRNA)及蛋白的变化,并观察氯沙坦对这些变化的影响以期评估氯沙坦的抗心律失常作用及其分子机制.方法:将SHR按随机数字表法分成以下三组(每组n=10):氯沙坦组、依那普利组和安慰剂组,另选同龄Wistar大鼠作为空白对照(对照组,n=10).8周后采用膜片钳技术记录左心室心肌ICa-L,并采用逆转录-聚合酶链反应及蛋白质印迹方法测定CaL-α1C的mRNA及蛋白水平.结果:氯沙坦组左心室细胞的50%动作电位持续时间、90%动作电位持续时间比安慰剂组、依那普利组缩短(P均<0.01).氯沙坦组的ICa-L峰值及电流密度比安慰剂组及依那普利组降低(P均<0.05).氯沙坦组ICa-L的τ值比安慰剂组及依那普利组升高(P均<0.01).氯沙坦组的CaL-α1C mRNA及蛋白表达水平比安慰剂组及依那普利组降低(P均<0.05).上述比较差异均有统计学意义.结论:氯沙坦能缩短单个心肌细胞动作电位时程,延迟L型钙通道失活再激活的恢复时间,通过下调CaL-α1CmRNA及其蛋白水平而发挥作用.     

Diazoxide对乳鼠窦房结细胞模拟缺血-再灌注时的保护作用研究

目的 :探讨K+ ATP通道开放剂diazoxide对模拟缺血 再灌注 (I/R)时培养乳鼠窦房结细胞的保护作用及其可能机制。方法 :分离乳鼠窦房结细胞 ,纯化培养 2d后进行实验。随机分为对照组、模拟I/R组、dia zoxide干预 (D +I/R)组及K+ ATP通道阻断剂 5 HD干预——— 5 HD +D +I/R组及 5 HD +I/R组。以流式细胞术检测各组窦房结细胞存活率 ;用激光共聚焦显微镜测定各组窦房结细胞内Ca2 + 。并采用全细胞膜片钳技术测定各组细胞L型钙电流 (L ICa)密度。结果 :①D +I/R组窦房结细胞存活率 [(6 1.4 3± 5 .14 ) % ]较I/R组 [(5 1.79±6 .2 8) % ]增加 (P <0 .0 1) ;5 HD +D +I/R组 [(5 2 .35± 4 .94 ) % ]及 5 HD +I/R组 [(5 3.16± 5 .35 ) % ]明显增高 ,均P <0 .0 1;②D +I/R组窦房结细胞相对荧光值较I/R组、5 HD +D +I/R组及 5 HD +I/R显著降低 ,均P <0 .0 1;③D +I/R组窦房结细胞L ICa密度较I/R组及 5 HD +D +I/R组明显增加 ,均P <0 .0 1。结论 :diazoxide降低窦房结细胞内钙负荷 ,对模拟I/R时的培养乳鼠窦房结细胞有保护作用 ,并可对抗模拟I/R对培养乳鼠窦房结细胞L ICa的影响 ,该作用可能与细胞线粒体K+ ATP通道的开放有关。     

M2受体和IKACh在犬室上组织的分布特点及胺碘酮对IKACh和胆碱能心房颤动的影响

目的 研究迷走神经刺激(VS)诱发心房颤动(房颤)的情况及M2受体和IKACh在犬心房、心耳及其相邻大静脉的分布特点及胺碘酮对IKACh的影响,探讨其治疗胆碱能房颤的机制.方法 10只犬分别给予切断迷走神经、VS、VS+胺碘酮(分别做为对照组、VS组和胺碘酮组)后,观察心房肌动作电位(APD)的变化及诱发房颤的情况.后分离出左右心耳、左右心房、肺静脉和上腔静脉,用Western印记法观察M2受体蛋白在上述组织的分布;并用组织块酶解法分离左右心耳、左右心房、肺静脉和上腔静脉的单个细胞,采用膜片钳全细胞法观察IKACh在上述部位的离子流密度;观察应用胺碘酮后IKACh的变化.结果 对照组无一例诱发出房颤;VS组4例诱发房颤,诱发率为40%;胺碘酮组1例诱发房颤,诱发率为10%.胺碘酮组诱发房颤的比率比VS组有明显降低(P＜0.05).IKACh在左右心房都表现出强的内向整流性,在超极化有逐渐升高的内向电流,而在去极化表现快速衰减的外向电流,M2受体和IKACh电流密度显示在左右心耳和左心房比右心房、肺静脉和上腔静脉高[M2受体0.66±0.08,0.67±0.08 and 0.51±0.06 vs 0.35±0.04,0.33±0.04 and 0.32±0.03,P＜0.05;IKACh(20.36±0.91)pA/pF,(21.34±0.92)pA/pF and(14.17±0.65)pA/pF vs(10.34±0.62)pA/pF,(8.24±0.45)pA/pF and(7.65±0.42)pA/pF,P＜0.05];2 mM胺碘酮阻断后,IKACh密度明显降低,左右心房的IKACh密度没有明显差异,但心耳的密度仍比心房高.结论 M2受体和IKACh电流密度在心耳明显高于心房和相邻静脉的分布,心耳可能在胆碱能房颤诱发中有重要作用,而肺静脉和上腔静脉的作用较小;胺碘酮可以阻断IKACh并减少左右心房IKACh大小的差异,此可能是其治疗胆碱能房颤的机制.     

渗透压对大鼠心室肌细胞L型Ca2+电流的影响

目的 :观察细胞胞外渗透压的改变对大鼠心室肌 L型 Ca2 +（ICa,L）电流的影响。方法 :采用全细胞膜片钳技术记录大鼠心室肌细胞 ICa,L。结果 :细胞外的渗透压由 3 10 m Osm / kg H2 O降低至 2 2 0 m Osm/ kg H2 O可使 ICa,L的 rundown明显变慢 ,电流大小无统计学意义上的差异 ;而当其中细胞外的渗透压由 3 10 m Osm/ kg H2 O升高至 410m Osm/ kg H2 O时可使 ICa,L减小 （5 1.4± 7.9） % （n=4,P<0 .0 1）。结论 :细胞外渗透压变化对大鼠心室肌基础 ICa,L有明显影响