钙调蛋白激酶Ⅱ抑制剂对肥厚心肌细胞早期后除极的影响

目的:探讨钙调蛋白激酶Ⅱ特异性抑制剂KN-93对肥厚心肌细胞动作电位时程(APD)及早期后除极(EAD)发生率的影响。方法:选取雌性新西兰大白兔,通过缩窄腹主动脉制备兔心肌肥厚模型(LVH组),并设假手术组(sham组)作对照比较,仅游离腹主动脉,未进行缩窄。8周后,应用超声心动图观察左心室肥厚程度。采用胶原酶消化法分离单个心肌细胞,应用全细胞膜片钳技术记录动作电位(AP),分别给予低钾(2mmol/L)、低镁(0.25mmol/L)台氏液灌流(sham组、LVH组)、含KN-92(KN-92组)、KN-93(KN-93组)的低钾、低镁台氏液灌流,观察慢频率电刺激(0.25～0.5Hz)条件下各组心肌细胞EAD的发生率,同时观察KN-92、KN-93对肥厚心肌细胞APD的影响。结果:8周后,与Sham组相比,心肌肥厚组的心脏外形明显增大,左室壁明显增厚,模型建立成功。电流钳模式下记录动作电位,在低钾、低镁台氏液灌流及慢频率电刺激下,Sham组、LVH组、KN-92组(0.5μmol/L)及KN-93组(0.5μmol/L)EAD的发生率分别为0/12、11/12、10/12和5/12。当KN-92组及KN-93组中药物浓度增至1μmol/L时,肥厚心肌细胞EAD的发生率分别为10/12和2/12,同时其对APD无明显影响(P>0.05)。结论:钙调蛋白激酶Ⅱ特异性抑制剂KN-93能够有效抑制肥厚心肌EAD的发生,这可能是其抗肥厚心肌室性心律失常发生的主要作用机制。     

钙调蛋白激酶II抑制剂KN-93对离体肥厚大鼠心脏电生理特性的影响

KN-93是钙调蛋白激酶II特异性抑制剂,被广泛应用于基础研究,且显现出良好的抗心律失常作用。然而关于KN-93对整体心脏电生理特性影响的研究较少,本研究旨在阐明KN-93对离体肥厚心脏电生理特性的影响,阐明KN-93抗心律失常的特性。方法：雄性SD大鼠40只,随机分为假手术组(Sham组)、心肌肥厚组(Hypertrophy,HY组)。缩窄腹主动脉制作心肌肥厚模型。手术6周后,超声心动图评价模型;运用Langendorff心脏离体灌流电生理技术检测整体心脏电生理特性,微电极阵列技术评价心脏传导情况。结果：手术6周后,左室后壁舒张末期厚度及室间隔舒张末期厚度明显增厚,提示心肌肥厚造模成功。与Sham组相比,HY组心室各部位的单向动作电位时程(APD90)显著延长(P均<0.01),有效不应期(ERP)也显著延长(P均<0.01);诱发动作电位电交替阈值中位数明显增大(P<0.01);传导的时间离散度明显增大(P<0.01),且室性心律失常的诱发率明显升高(P<0.05)。HY组使用CaMKII抑制剂KN-93后,APD90和ERP并无显著变化,APD电交替阈值也无明显改变,但传导的时间离散度明显减小(P<0.001),室性心律失常的诱发率减少(P<0.05)。结论：CaMKII抑制剂KN-93对离体肥厚大鼠心脏APD90、ERP、 APD电交替阈值均无明显影响,但能显著减小传导速度离散度;对传导的影响可能是KN-93抗心律的重要机制。     

厄贝沙坦对兔肥厚心肌钙调蛋白激酶活性及室性心律失常发生的影响

目的:研究厄贝沙坦对兔肥厚心肌局部钙调蛋白激酶活性的影响和对恶性心律失常发生的预防作用。方法:家兔30只,随机分为左心室肥厚组(手术组,腹主动脉缩窄术制备心肌肥厚模型),对照组(只暴露主动脉而不行缩窄)和厄贝沙坦干预组(干预组,行腹主动脉缩窄后予厄贝沙坦口服)。8周后,在体同步测量肥厚心肌3层的APD100以及透壁弥散复极化(TDR),用程序电刺激方法诱导心律失常发生。术后测量全心重量、室壁厚度和心肌局部钙调蛋白激酶活性。结果:手术组,3层心肌细胞的APD100,TDR较对照组明显延长,局部钙调蛋白激酶活性明显升高,更容易诱发室性心律失常;干预组APD100、TDR较手术组缩短,局部钙调蛋白激酶活性降低,而且不易诱发心律失常。结论:肥厚心肌发生电生理重构,局部钙调蛋白激酶活性增加,更容易发生恶性心律失常,厄贝沙坦能够部分恢复肥厚心肌的电重构,降低心肌局部的钙调蛋白激酶活性,从而减少心律失常的发生。     

胺碘酮对肥厚心肌钙调蛋白激酶活性的影响

目的观察口服胺碘酮对肥厚心肌细胞钙调蛋白激酶(CaMK)活性的影响,探讨胺碘酮抗心律失常的作用机制。方法30只家兔随机分为假手术组、心肌肥厚组和胺碘酮组,每组10只,喂养3个月,制备兔左室楔形心肌块。同步记录楔形心肌块容积心电图和内、外膜心肌细胞跨膜动作电位(TAP),程序电刺激诱发室性心律失常,并观察各组QT间期、跨室壁复极离散度(TDR)、早期后除极(EAD)和尖端扭转型室性心动过速(Tdp)的诱发率。利用放射免疫法测定心肌细胞CaMK活性。结果胺碘酮组和心肌肥厚组QT间期、内外膜心肌细胞TAP复极90%时程(APD90)和TDR均较假手术组明显延长(P<0.01),胺碘酮组QT间期和内、外膜心肌细胞APD90与心肌肥厚组相比进一步延长(P<0.05),但对TDR无明显影响。与假手术组比较,心肌肥厚组EAD和Tdp的发生率较假手术组明显升高(P<0.01),胺碘酮组EAD和Tdp的发生率较心肌肥厚组降低(P<0.05)。心肌肥厚组心肌细胞CaMK活性较假手术组明显升高,胺碘酮组CaMK活性较心肌肥厚组降低(P均<0.05)。结论胺碘酮抗心律失常的作用机制可能部分与抑制CaMK活性有关。     

钙调蛋白抑制剂对陈旧性心肌梗死兔室性心律失常的影响

探讨钙调蛋白抑制剂W 7对陈旧性心肌梗死(HMI)兔室性心律失常的影响,将 30只雄性日本大耳白兔随机分假手术组(Sham)、HMI组和W 7干预组。Sham组开胸但不结扎冠状动脉;HMI组和W 7干预组开胸并结扎冠状动脉左室支制备心肌梗死模型,喂养 3个月后进行研究。W 7干预组在程序刺激前以 50μmol/kg的剂量溶于20ml生理盐水中,在 10min内静脉推注,HMI组和Sham组静脉推注生理盐水。将双极电极刺入左室梗死周边部位及Sham组的相应部位,程序刺激诱发心律失常,记录室性心动过速的发生率,测定心室颤动阈值。结束实验后取出心脏并称量左室重量。结果:Sham组、HMI组和W 7组诱发室性心动过速的发生率分别为 0 /10、8 /10和 3 /10。Sham组与HMI组差异有显著性(P<0. 01);W 7组与HMI组相比较室性心律失常发生率降低,差异有统计学意义(P<0. 05)。三组的心室颤动阈值分别为 13. 30±0. 95V、8. 90±1. 37V和 11. 80±1. 14V,三组之间差异均有显著性(P<0. 01)。结论:钙调蛋白抑制剂能提高HMI兔的心室颤动阈值,降低室性心律失常的发生率。     

钙/钙调蛋白依赖的蛋白激酶Ⅱ与心律失常的研究进展

钙/钙调蛋白依赖的蛋白激酶Ⅱ(CaMKⅡ)能通过调节离子通道和钙转运参与心肌细胞电活动,而诸如心力衰竭、心房颤动、急性心肌梗死等多种疾病和缺血-再灌注等病理状态都会导致CaMKⅡ的过度激活,继而通过其下游信号通路改变心肌细胞的电生理状态,导致心律失常的发生。研究表明,下调CaMKⅡ的活性能在某种程度上减少心律失常的发生,改善心肌细胞的功能。因此,CaMKⅡ有望成为新的抗心律失常靶点。     

钙介导的信号转导途径与心肌肥厚

心肌肥厚是临床上许多心血管疾病共有的病理过程，晚期可导致严重的心律失常和心衰。其发病机制与压力负荷增加、神经内分泌因素、钙超载、原癌基因等密切相关。其中细胞内Ca^2＋浓度升高是心肌肥厚信号转导发生、发展的中心环节。目前认为有两种钙介导的信号转导机制参与了心肌肥厚的发生与发展：一是钙调神经磷酸酶（CaN）介导途径；二是钙调素依赖性蛋白激酶Ⅱ（CaMKⅡ）信号转导途径。     

钙调蛋白激酶Ⅱ参与Timothy综合征心律失常的发生机制

背景Timothy综合征（TS）是一种细胞Ca2＋过度内流、容易发生致命性心律失常的疾病，系因原发性心脏L型Ca2＋通道（Cav，1．2）突变所致。突变后的Cav，1．2电流（LCa）失去正常的电压依赖性灭活机制，在细胞Ca2＋超载的情况下，钙调蛋白依赖性蛋白激酶Ⅱ（CaMKⅡ）活化后将会引起心律失常。我们猜测CaMKⅡ可能参与TS心律失常的发生机制。     

钙离子/钙调蛋白依赖性蛋白激酶Ⅱ与心律失常及心力衰竭的研究进展

钙离子/钙调蛋白依赖性蛋白激酶Ⅱ（CaMKⅡ）是一种重要的丝氨酸/苏氨酸蛋白激酶,它能通过调节离子通道和钙转运参与心肌细胞的心电活动。研究表明,CaMKⅡ是心律失常的关键酶,当其活性增高,通过影响相关离子通道,导致心房颤动、长QT综合征、儿茶酚胺敏感性多形性室性心动过速等各种心律失常和心力衰竭;抑制CaMKⅡ活性能减少心律失常的发生,因此,CaMKⅡ是潜在的新型抗心律失常药物靶点。     

钙调神经磷酸酶和丝裂素活化蛋白激酶在调节心肌肥厚中的作用

钙调神经磷酸酶和丝裂素活化蛋白激酶信号系统是调节心肌肥厚发生和发展的两条重要细胞信号通道;前者在体内病理因素刺激下活性增高而导致心肌肥厚形成,后者的3个成员胞外信号调节激酶、应激活化蛋白激酶和P38丝裂素活化蛋白激酶,在调节心肌肥厚中的作用则不同。另外,两者之间并不是孤立的,而是彼此交叉、互相协调、共同调节心肌肥厚反应。     

钙调蛋白激酶Ⅱ抑制剂对心肌肥厚兔室性心律失常的影响

目的观察钙调蛋白激酶Ⅱ抑制剂KN-93对心肌肥厚兔室性心律失常的影响。方法雌性新西兰大白兔随机分为4组：假手术组（Sham组）、心肌肥厚组（LVH组）、心肌肥厚＋KN-93组（KN-93组）、心肌肥厚＋KN-92组（KN-92组）,每组10只。LVH、KN-93及KN-92组通过缩窄腹主动脉制备兔心肌肥厚模型,Sham组仅游离腹主动脉未进行缩窄。8周后制备兔左室楔形心肌块的灌注模型,同步记录心内、外膜动作电位及跨壁心电图,观察低钾（2mmol／L）、低镁（0．25mmol／L）台氏液灌流及慢频率刺激条件下各组早期后除极（EAD）和尖端扭转型室性心动过速（Tap）的发生率,并记录在不同起搏周期下QT间期、动作电位时程（APD）及跨室壁复极离散度（TDa）的变化。结果在低钾、低镁台氏液灌流及2000～4000hi8慢频率刺激下,Sham、LVH、KN-92组（0．5μmol／L）及KN-93组（0．5μmol/L）EAD的发生率分别为0／10、10／10、9／10和5／10,Tdp的发生率分别为0／10、5／10、4／10和1／10;当KN-92组及KN-93组中药物浓度增至1μmol／L时,EAD的发生率分别为9／10和3／10,Tdp的发生率分别为4／10和1／10。而且KN-93组、KN-92组对QT间期、APD及TDR无明显影响（P〉0．05）。结论钙调蛋白激酶Ⅱ特异性抑制剂KN-93能够有效抑制心肌肥厚兔室性心律失常的发生,其主要作用机制是通过减少EAD的发生来实现。     

Ryanodine receptor phosphorylation, calcium/calmodulin-dependent protein kinase II, and life-threatening ventricular arrhythmias

Ryanodine receptor (RyR2) dysfunction, which may result from a variety of mechanisms, has been implicated in the pathogenesis of cardiac arrhythmias and heart failure. In this review, we discuss the important role of Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) in the regulation of RyR2-mediated Ca(2+) release. In particular, we examine how pathological activation of CaMKII can lead to an increased risk of sudden arrhythmic death. Finally, we discuss how reduction of CaMKII-mediated RyR2 hyperactivity might reduce the risk of arrhythmias and may serve as a rationale for future pharmacotherapeutic approaches.     

Effect of diuretic therapy on ventricular arrhythmias in hypertensive patients with or without left ventricular hypertrophy

Recent studies have suggested that hypertensive patients with ECG evidence of left ventricular hypertrophy (LVH) may have increased risk of sudden death when treated with diuretics. In the present study echocardiography was used as a more sensitive index for the presence of LVH. Thirty-one patients with uncomplicated hypertension underwent 48-hour ambulatory ECG monitoring both before any treatment and after 4 weeks of hydrochlorothiazide, (HCTZ), 100 mg daily. In 18 patients with left ventricular posterior wall thickness (LVPWT) greater than or equal to 13 mm (average = 14.4 +/- 0.2 mm) on echocardiogram, plasma potassium decreased from 4.1 +/- 0.3 to 3.3 +/- 0.4 mEq/L with HCTZ (p less than 0.01). Premature ventricular contractions (PVCs) averaged 5.7 +/- 9.9/hr at baseline and 7.1 +/- 16.6/hr following HCTZ (p = NS). The total number of couplets was 29 before and 13 after HCTZ, while four brief runs of ventricular tachycardia occurred only before treatment. In the remaining 13 patients with LVPWT less than or equal to 12 mm (average = 11.2 +/- 0.1 mm), plasma potassium decreased from 4.1 +/- 0.3 to 3.4 +/- 0.5 mEq/L with HCTZ (p less than 0.01). The average number of PVCs was 4.3 +/- 8.0/hr after HCTZ (p = NS). One couplet and one 3-beat run of ventricular tachycardia occurred before and one 3-beat run of ventricular tachycardia after HCTZ. Although more complex arrhythmias were noted in the LVH group, the differences were not statistically significant. These results indicate that thiazide therapy does not increase ventricular arrhythmias either in patients with or without LVH.     

Risk of ventricular arrhythmias in hypertensive men with left ventricular hypertrophy

The echocardiographic predictors of ventricular arrhythmias are reported for the Hypertension Arrhythmia Reduction Trial. Men with mild hypertension were withdrawn from their diuretic therapy and repleted with 40 mEq/day of oral potassium and 20 mEq/day of oral magnesium for 1 month. M-mode echocardiography and 24-hour continuous ambulatory electrocardiography were performed on 123 men, mean age 62 years. Forty-eight men (39%) had echocardiographic evidence of left ventricular (LV) hypertrophy defined as an LV mass index greater than 134 g/m2 and this finding was not related to the presence of LV hypertrophy on electrocardiogram or to age. Men who had echocardiographic LV hypertrophy were more likely than men without echocardiographic LV hypertrophy to have greater than or equal to 30 ventricular premature complexes (VPCs)/hr (odds ratio = 2.7; 95% confidence interval = 0.9, 8.0), multiform extrasystoles (odds ratio = 1.7; confidence interval = 0.8, 3.7), episodes of ventricular tachycardia (odds ratio = 2.3; confidence interval = 0.7, 7.1) and the combination of frequent (greater than or equal to 30 VPCs/hr) or complex (ventricular couplets, multiform extrasystoles or episodes of ventricular tachycardia) ventricular arrhythmia (odds ratio = 1.7; confidence interval = 0.8, 3.5). Similar associations between echocardiographic LV hypertrophy and ventricular arrhythmias were observed on 24-hour tracings obtained on entry to the study (before electrolyte repletion) in the 96 men who were taking diuretics at this time. The combination of a frequent or complex arrhythmia was also more common in men aged 60 to 70 compared to men aged 35 to 59 (odds ratio = 3.4; confidence interval = 1.4, 8.2).(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of gallopamil on electrophysiologic abnormalities and ventricular arrhythmias associated with left ventricular hypertrophy in the feline heart.

Left ventricular hypertrophy increases vulnerability to ventricular fibrillation. To determine whether calcium channel blockade protects against ventricular arrhythmia in left ventricular hypertrophy, we studied the effects of gallopamil, a potent and specific calcium channel antagonist, in 37 cats undergoing aortic banding (group 1, n = 28) or a sham procedure (group 2, n = 9). Each cat underwent serial echocardiography and was studied after the development of left ventricular hypertrophy, defined as an increase of at least 30% in left ventricular posterior wall thickness. After baseline electrophysiologic testing, animals received gallopamil (70 micrograms/kg loading dose followed by 2.5 micrograms/kg/min infusion) (n = 19) or a control infusion of saline solution (n = 18), and testing was repeated. There was no significant difference between groups 1 and 2 in baseline excitability thresholds intraventricular conduction times, ventricular effective refractory periods, or monophasic action potential durations. Thresholds for induction of ventricular fibrillation were lower in group 1 than in group 2, and only in group 1 was ventricular fibrillation inducible during programmed stimulation. This altered vulnerability was associated with a significantly greater dispersion of excitability thresholds, ventricular effective refractory periods, and monophasic action potential durations. Gallopamil did not change baseline measurements except for prolonging sinus cycle length and atrioventricular conduction time.(ABSTRACT TRUNCATED AT 250 WORDS)     

A purine analog kinase inhibitor, calcium/calmodulin-dependent protein kinase II inhibitor 59, reveals a role for calcium/calmodulin-dependent protein kinase II in insulin-stimulated glucose transport

Olomoucine is known as a cyclin-dependent kinase inhibitor. We found that olomoucine blocked insulin's ability to stimulate glucose transport. It did so without affecting the activity of known insulin signaling proteins. To identify the olomoucine-sensitive kinase(s), we prepared analogs that could be immobilized to an affinity resin to isolate binding proteins. One of the generated analogs inhibited insulin-stimulated glucose uptake with increased sensitivity compared with olomoucine. The IC(50) for inhibition of insulin-stimulated glucose uptake occurred at analog concentrations as low as 0.1 microM. To identify proteins binding to the analog, [(35)S]-labeled cell lysates prepared from 3T3-L1 adipocytes were incubated with analog chemically cross-linked to a resin support and binding proteins analyzed by SDS-PAGE. The major binding species was a doublet at 50-60 kDa, which was identified as calcium/calmodulin-dependent protein kinase II (CaMKII) by N-terminal peptide analysis and confirmed by matrix-assisted laser desorption ionization-mass spectrometry as the delta- and beta-like isoforms. To investigate CaMKII involvement in insulin-stimulated glucose uptake, 3T3-L1 adipocytes were infected with retrovirus encoding green fluorescent protein (GFP)-hemagluttinin tag (HA)-tagged CaMKII wild-type or the ATP binding mutant, K42M. GFP-HA-CaMKII K42M cells had less kinase activity than cells expressing wild-type GFP-HA-CaMKII. Insulin-stimulated glucose transport was significantly decreased (approximately 80%) in GFP-HA-CaMKII K42M cells, compared with nontransfected cells, and cells expressing either GFP-HA-CaMKII or GFP-HA. There was not a concomitant decrease in insulin-stimulated GLUT4 translocation in GFP-HA-CaMKII K42M cells when compared with GFP-HA alone. However, insulin-stimulated GLUT4 translocation in GFP-HA-CaMKII cells was significantly higher, compared with either GFP-HA or GFP-HA-CaMKII K42M cells. Our results implicate the involvement of CaMKII in glucose transport in a permissive role.     

Significance of ventricular arrhythmias in systemic hypertension with left ventricular hypertrophy.

Hypertensive patients with the electrocardiographic (ECG) pattern of left ventricular (LV) hypertrophy and strain are at increased risk of sudden death. It has been suggested that ventricular arrhythmias may be responsible. The prevalence and significance of ventricular arrhythmias was therefore studied in 90 hypertensive patients with LV hypertrophy and strain by undertaking 48-hour ambulatory ECG monitoring, ECG signal-averaging and programmed ventricular stimulation. Complex ventricular ectopic activity (Lown grade greater than or equal to 3) was detected in 59 patients (66%). Eleven patients (12%) had episodes of nonsustained ventricular tachycardia. There were no sustained arrhythmias either on ambulatory ECG monitoring or induced by programmed ventricular stimulation. Only 1 patient had ventricular late potentials recorded by the signal-averaged electrocardiogram. Therefore, there was little to suggest an underlying arrhythmogenic substrate in these patients. In conclusion, whereas ventricular arrhythmias occur often in patients with LV hypertrophy associated with systemic hypertension, their significance, if any, remains to be established.