Electrophysiological properties of the propafenone-analogue GE 68 (1-[3-(phenylethyl)-2-benzofuryl]-2-(propylamino)-ethanol) in isolated preparations and ventricular myocytes of guinea-pig hearts

GE 68 ((Rac.)-1-[3-(Phenylethyl)-2-benzofuryl]-2-(propylamino)-ethanol hydrochloride) is structurally related to propafenone, and exerts negative inotropic and negative chronotropic effects similar to the parent drug, but lacks any β-adrenoceptor blocking activity contrary to propafenone. Thus, the electrophysiological effects of GE 68 were studied in papillary muscles, left atria, Purkinje fibres, sinoatrial nodes and ventricular myocytes of the guinea-pig heart with the intracellular microelectrode technique and the patch-clamp technique in the cell-attached mode. The decrease of the maximum upstroke velocity (V˙_max) by GE 68 (1 to 10 μM) was use- and frequency-dependent. V˙_max recovered from the use-dependent block with a time constant of 4.1 ± 0.6 s. In papillary muscles and Purkinje fibres action potential duration was shortened, while it was prolonged in left atria and sinoatrial nodes. Half-maximal steady-state inactivation of the sodium channels was shifted to more negative membrane potentials (control: –91.5 ± 0.8 mV, 10 μM GE 68: –97.9 ± 2.5 mV). The peak of the current-voltage relationship and the reversal potential were not changed by GE 68. The amplitude of the unitary current remained unaltered, while open state probability was decreased. The most striking effect of GE 68 was an increase of the number of sweeps without single channel openings (1 μM: 2 fold, 10 μM: 6 fold). GE 68 also caused a decrease of the mean open times, and an increase of the mean closed times in unmodified and pronase-modified sodium channels. Besides the lack of β-adrenoceptor blocking activity, data present a faster recovery from the use-dependent block by GE 68 and a lower affinity to inactivated sodium channels compared to the reference drug propafenone, as well as differences in the effect on single channel kinetics. Received: 25 July 1996 / Accepted: 14 October 1996     

Pharmacology of KB‐R7943: A Na+–Ca2+ exchange inhibitor

The Na⁺–Ca²⁺ exchange (NCX) system plays a pivotal role in regulating intracellular Ca²⁺ concentration in cardiomyocytes, neuronal cells, kidney and a variety of other cells. It performs a particularly important function in regulating cardiac contractility and electrical activity. One of the leading NCX inhibitors is KB‐R9743 (KBR) that appears to exhibit selectivity for Ca²⁺‐influx‐mode NCX activity (reverse mode of NCX). In this article we reviewed pharmacology of KBR and provide a brief summary of studies with other NCX inhibitors, such as SEA0400 (SEA) and SN‐6 (SN). Potential clinical usefulness of KBR and other NCX inhibitors is still controversial but the reviewed findings may be helpful in designing more selective and clinically useful NCX inhibitors for the treatment of cardiac, neuronal and kidney diseases.     

人类胚胎生殖细胞体外分化为心肌细胞的研究

胚胎生殖（EG）细胞是来源于胚胎原始生殖细胞（PGCs）的多潜能干细胞。采用无饲养层细胞、无细胞因子等的基础培养液（DMEM＋20％NBS＋0．1mM 2Me）培养EG细胞，部分在基础培养液添加10μmol／LRA＋0．75％DMSO或10μmol／L 5-氮胞苷（5-AZA）诱导人类EG细胞向心肌细胞分化，以检测其是否具有向心肌细胞自发分化的能力。9例（8．49％，9／106）胎儿EG细胞在体外分化得到20个节律性心脏跳动样细胞团，其搏动节律为20～120次／min，体外维持节律性搏动最短2d，最长至15d，呈PAS，Myoglobin，α-actin阳性；对K^＋、Ca^＋、肾上腺素等具有与在体心脏相似的反应性；透射电镜观察具有心肌细胞样结构。添加DMSO和RA或5-AZA诱导未得到跳动样心肌细胞，但可提高心肌α-actin免疫组织化学染色阳性率；表明人类胚胎生殖细胞具有向心肌细胞分化的潜能。     

Pharmacological characterization of A1 adenosine receptors in isolated rat ventricular myocytes

Summary The aim of the present study was the characterization of adenosine receptors in isolated rat ventricular myocytes. The CAMP-levels of rat ventricular myocytes in the presence of 1 mol/l isoprenaline were reduced by up to 48% by adenosine analogues; the rank order of potency was: R-N⁶-phenylisopropyladenosine (IC₅₀ 60 nmol/1), 5-N-ethylcarboxamidoadenosine (IC₅₀ 360 nmol/l) and S-N⁶-phenylisopropyladenosine (IC₅₀ 16 ol/l). The adenosine receptor antagonist XAC (xanthine amine congener) antagonized the effect of R-N⁶-phenylisopropyladenosine in a concentration-dependent manner with a K_i-value of 20 nmol/l. The A₁ receptor-selective radioligand R-N⁶-¹²⁵I-p-hydroxyphenylisopropyladenosine bound to membranes prepared from rat ventricular myocytes in a saturable manner with a B _max of 17.7 fmol/mg protein and a K _D-value of 1.1 nmol/l. Adenosine analogues competed for the binding with the same rank order of potency as for the inhibition of the isoprenaline-induced cAMP-increase. GTP inhibited radioligand binding with an IC₅₀-value of 73 ol/l. These results suggest the presence of A₁ adenosine receptors on rat ventricular myocytes, which mediate an inhibition of adenylate cyclase. The receptors may be responsible for the effects of adenosine and its analogues on the heart.Abbreviations ¹²⁵I-HPIA R-N⁶-¹²⁵I-p-hydroxyphenylisopropyladenosine - PIA N⁶-phenylisopropyladenosine - NECA 5-N-ethyl-carboxamidoadenosine - XAC 8-4-[([(2-aminoethyl)aminocarbonyl]methyl)oxy]phenyl-1,3-dipropylxanthine (xanthine amine congener) - Ro 20-1724 4-(3-butoxy-4-methoxybenzyl)-2-imidazolidinone - ScAMPTME 2-O-monosuccinyladenosine-3,5-cyclic monophosphate tyrosyl methyl ester - HEPES N-2-hydroxyethylpiperazine-N-2-ethanesulfonic acid - GTP guanosine-5-tri-phosphate Send offprint requests to D. Martens     

参附注射液对缺氧心肌细胞凋亡的抑制效应

目的　探讨参附注射液对缺氧诱导的培养乳鼠心肌细胞凋亡的作用。方法　将 SD乳鼠的培养心肌细胞随机分为三组:对照组、缺氧72 h组和参附注射液组。缺氧 72 h前加入1 mmol参附注射液。应用TUNEL法及流式细胞仪分析心肌细胞凋亡的变化,借助半胱胺酸 天门冬胺酸酶(caspase- 3)荧光分析试剂盒,荧光比色法检测心肌细胞凋亡过程中 caspase -3 活性的变化。结果　TUNEL及流式细胞仪分析显示,参附注射液组 AI值和细胞凋亡百分率分别为(14. 10±2 .56)%和(14. 93±2 .47)%,明显低于缺氧72 h组(46 .49±4 .93)%和(48 .43±4 .18)%(P<0 .01)。caspase -3活性检测显示,参附注射液组的caspase- 3活性比缺氧72 h组降低了 52. 85%(P<0. 01)。结论　参附注射液能明显抑制缺氧诱导的心肌细胞凋亡。caspase- 3蛋白酶活性抑制可能是其机理之一。     

Endogenous glycogen prevents Ca2+ overload and hypercontracture in harp seal myocardial cells during simulated ischemia

The purpose of this study was to determine if elevated myocardial glycogen content could obviate Ca(2+) overload and subsequent myocardial injury in the setting of low oxygen and diminished exogenous substrate supplies. Isolated harp seal cardiomyocytes, recognized as having large glycogen stores, were incubated under conditions simulating ischemia (oxygen and substrate deprivation) for 1 h. Rat cardiomyocytes were used for comparison. Freshly isolated seal cardiomyocytes contained approximately 10 times more glycogen than those from rats (479 +/- 39 vs. 48 +/- 5 nmol glucose/mg dry weight (dry wt), mean +/- S.E., n = 6), and during ischemia lactate production was significantly greater in seal compared to rat cardiomyocytes (660 +/- 99 vs. 97 +/- 14 nmol/mg dry wt), while glycogen content decreased both in seal (from 479 +/- 39 to 315 +/- 58 nmol glucose/mg dry wt) and rat cardiomyocytes (from 48 +/- 5 to 18 +/- 5 nmol glucose/mg dry wt). Cellular ATP was well maintained in ischemic seal cardiomyocytes, whereas it showed a 65% decline (from 31 +/- 3 to 11 +/- 1 nmol ATP/mg dry wt) in rat cardiomyocytes. Similarly, total seal cardiomyocyte Ca(2+) content was not affected by ischemia, while Ca(2+) increased from 8.5 +/- 2.0 to 13.3 +/- 2.0 nmol/mg dry wt in ischemic rat myocytes. Rat cardiomyocytes also showed a notable decline in the percentage of rod-shaped cells in response to ischemia (from 66 +/- 4% to 30 +/- 3%), and cell morphology was unaffected in seal incubations. Addition of iodoacetate (IAA, an inhibitor of glycolysis) to seal cardiomyocytes, on top of substrate and oxygen deprivation, reduced the cellular content of ATP by 52.9 +/- 4.4% (from 25 +/- 4 to 11 +/- 2 nmol ATP/mg dry wt) and the percentage of rod-shaped myocytes from 51 +/- 3% to 28 +/- 4%, while total Ca(2+) content was unchanged by these conditions. Seal cardiomyocytes thus tolerate low oxygen conditions better than rat cardiomyocytes. This finding is most likely due to a higher glycolysis rate in seals, fueled by larger myocardial glycogen stores.     

α_2-肾上腺素能受体激动剂B-TH933抑制LPS处理的心肌细胞释放TNF-α

目的:观察α2-肾上腺素能受体激动剂B-HT933对脂多糖(LPS)刺激的心肌细胞产生肿瘤坏死因子α(TNF-α)的影响,并初步分析其作用机制。方法:分离培养SD大鼠乳鼠心肌细胞。利用免疫荧光染色观察心肌α2A-肾上腺素能受体的分布;B-HT933和/或LPS处理心肌细胞一定时间后,用ELISA方法检测细胞培养液中TNF-α的含量、实时荧光定量PCR测定心肌细胞TLR4和TNF-αmRNA的表达、Western blot分析心肌细胞中相关信号分子的磷酸化水平。结果:免疫荧光染色证实乳鼠心肌细胞中存在α2A-肾上腺素能受体。LPS以剂量和时间依赖的方式刺激心肌细胞产生TNF-α,0.1μmol/L的B-HT933处理能显著抑制LPS诱导的TNF-αmRNA的表达和TNF-α蛋白的产生。而且,BHT能抑制LPS诱导的心肌细胞IκBα的磷酸化。结论:乳鼠心肌细胞上存在α2A-肾上腺素能受体,其激动剂B-HT933可能通过抑制心肌细胞IκBα的磷酸化来减少LPS诱导的TNF-α产生。     

心肌肽素对豚鼠心室肌细胞钠通道的影响

目的： 研究心肌肽素对豚鼠心室肌细胞钠通道的影响，探讨心肌肽素在离子通道水平的作用机制。 方法： 用急性酶解分离法获得豚鼠心室肌细胞，标准全细胞膜片钳技术记录钠电流(I_Na)。 结果： 心肌肽素1、5、10、50、100、500 mg/L使豚鼠心室肌细胞I_Na分别减少(0±1)%、(6±2)%、(10±2)%、(15±1)%、(22±9)%、(30±6)%，呈浓度依赖性抑制I_Na。心肌肽素50 mg/L使I_Na激活时间(TTP)从(2.8±0.7) ms延长至(3.0±0.8) ms (P<0.05)；使I_Na电流密度-电压曲线上移，但不改变激活电位、峰电位、反转电位和I-V曲线的形状；不影响稳态激活曲线、稳态失活曲线和稳态失活后恢复曲线。 结论： 心肌肽素浓度依赖性抑制豚鼠心室肌细胞I_Na，可能是其抗心律失常作用的机制之一。     

晚期糖基化终产物改变心肌细胞自发钙火花形态学

 目的:本研究旨在探讨晚期糖基化终末产物（AGEs）对心肌细胞雷诺丁受体（RyR）活性的影响及钙调控作用,从而阐明糖尿病心肌病心脏功能障碍的潜在机制。方法:通过激光共聚焦显微成像技术在培养的乳鼠心肌细胞观察自发钙火花发放频率以及钙火花的形态。结果:与对照组相比,AGEs大幅度增加钙火花的发放频率,其中10 mg/L AGEs组增加48％（P<0.01）,50 mg/L组AGEs增加200％（P<0.01）;而150 mg/L组AGEs组增加110％（P<0.01）。AGEs改变自发钙火花的形态、降低钙火花的幅度、宽度和钙火花持续时间并增加心肌细胞静息期钙离子水平。结论: AGEs引起自发钙火花的发放频率,从而增强钙火花介导的肌浆网Ca2+漏流,增加心肌细胞静息期钙离子水平,这可能是引起糖尿病性心肌病收缩功能障碍的重要原因。     

参麦注射液对急性缺氧-复氧心肌细胞凋亡的影响

目的：观察参麦注射液对急性缺氧-复氧后心肌细胞凋亡的影响，并探讨其可能机制。 方法： 采用原代培养的大鼠心肌细胞，通过化学缺氧法使细胞缺氧5 min，再恢复氧供应15 min，复制心肌细胞缺氧-复氧（anoxia-reoxygenation, A/R）模型。Annexin V-FITC/PI双染色流式细胞仪检测细胞凋亡百分率；Fluo-3负载激光扫描共聚焦显微镜观察细胞内钙离子水平。 结果： A/R组心肌细胞凋亡百分率明显高于正常组，细胞内平均钙离子荧光强度也显著强于正常组（P<0.01）。参麦注射液组细胞凋亡率显著小于A/R组，同时细胞内钙超载也明显轻于A/R组（P<0.01）。 结论： 参麦注射液能有效抑制缺氧-复氧心肌细胞的凋亡，这种保护作用的机制之一可能是通过减轻细胞内Ca2+超负荷实现的。