Impaired contractile reserve in severe mitral valve regurgitation with a preserved ejection fraction

BACKGROUND: Impaired contractile reserve in chronic MR results from load-independent, myocyte contractile abnormalities. AIMS: Investigate the mechanisms of contractile dysfunction in chronic mitral valve regurgitation (MR). METHODS: Mild MR was produced in eight dogs followed by pacing induced left ventricular (LV) dilatation over eight months. In-vivo LV dP/dt was measured at several pacing rates. Contractile function was measured in isolated LV trabeculae and myocytes at several stimulation rates and during changes in extracellular [Ca2+]. Identical studies were performed with six control dogs. RESULTS: Chronic MR resulted in a preserved ejection fraction with decreased dP/dt (p<0.01). LV trabeculae demonstrated significantly lower developed force and a negative force-frequency relation with chronic MR (p<0.05). Myocytes exhibited a negative shortening-frequency relationship in both groups with a greater decline with chronic MR (p<0.001) paralleled by decreases in peak [Ca2+](i) transients. Increases in extracellular [Ca2+] abrogated the defects in force generation in trabeculae from animals with chronic MR. CONCLUSION: Even with a preserved EF, chronic severe MR results in a significant reduction in intrinsic contractile function and reserve. Functional impairment was load-independent reflecting a predominant defect in calcium cycling rather than impaired peak force generating capacity due to myofibrillar attenuation.     

The use of human cardiac tissue in biophysical research: the risks of translation

There has been increasing enthusiasm for biomedical research that focuses directly on human pathophysiology, in part fueled by the recent NIH roadmap initiative. While this approach has considerable merit, a myopic and primary focus on human disease and on human tissue introduces a plethora of research risks and concerns that could potentially complicate data interpretation and retard scientific progress. While some of these issues are generic when one extrapolates from animal models to the human circumstance, others are more specific to the cardiovascular system in general and to the study of cardiocyte biology in particular. This brief review will highlight some of these.     

益心口服液对化学性缺氧心肌细胞的保护作用

目的：探讨益心口服液对化学性缺氧心肌细胞的保护作用。方法：改良Simpson法培养新生大鼠心肌细胞,随机分为生理盐水对照组、缺氧模型组、复方丹参滴丸组及益心口服液大中小3个剂量组。采用二亚硫酸钠造心肌细胞化学性缺氧,并给予相应的药物干预。检测超氧化物歧化酶（SOD）、丙二醛（MDA）、乳酸脱氢酶（LDH）和丙酮酸激酶（PK）含量,观察益心口服液对化学性缺氧心肌细胞的影响。结果：与对照组心肌细胞相比,缺氧模型组心肌细胞变大,折光性差,胞核暗淡,细胞LDH和PK含量降低,细胞MDA含量增加,SOD活性降低（P〈0．05）。复方丹参滴丸组细胞PK含量降低,细胞MDA含量增加,SOD活性降低（P〈0．05）。益心口服液各剂量组SOD活性增加,LDH和PK含量增加,而MDA含量降低（P〈0．05）。未见剂量依从性。结论：益心口服液通过抗氧自由基,稳定细胞膜;降低心肌耗氧量,增加氧供需比等来减少缺氧心肌细胞损伤。     

蒺藜皂苷激活PKCε抗氧化应激诱导心肌细胞凋亡的机制

观察蒺藜皂苷 (gross saponins of Tribulus terrestris, GSTT) 在过氧化氢 (hydrogen peroxide, H₂O₂) 诱导新生大鼠心肌细胞凋亡过程中对蛋白激酶C Eplison亚型 (protein kinase C Eplison, PKCε) 及凋亡相关蛋白的影响, 探讨蒺藜皂苷抗心肌细胞凋亡的作用机制。新生大鼠心肌细胞原代培养, H₂O₂建立心肌细胞凋亡模型, 流式细胞术检测细胞凋亡率; Western blotting法检测phospho-PKCε及Bcl-2、Bax的蛋白含量; 免疫细胞化学技术检测cleaved caspase-3蛋白含量。与模型组比较, GSTT (100 mg·L^-1) 预处理可明显降低H₂O₂诱导的心肌细胞凋亡率 (P < 0.01), 并增加phospho-PKCε及Bcl-2的蛋白含量 (P < 0.01), 降低Bax及cleaved caspase-3的蛋白含量 (P < 0.01); PKC抑制剂白屈菜红碱 (chelerythrine, Che) 可部分阻断蒺藜皂苷抗心肌细胞凋亡作用, 与蒺藜皂苷组比较具有统计学意义 (P < 0.05, P < 0.01)。GSTT抗心肌细胞凋亡的作用机制可能与激活PKCε后抑制线粒体依赖的凋亡有关。     

IFN-α expression and antiviral effects are subtype and cell type specific in the cardiac response to viral infection

The interferon-β (IFN-β) response is critical for protection against viral myocarditis in several mouse models, and IFN-α or -β treatment is beneficial against human viral myocarditis. The IFN-β response in cardiac myocytes and cardiac fibroblasts forms an integrated network for organ protection; however, the different IFN-α subtypes have not been studied in cardiac cells. We developed a quantitative RT-PCR assay that distinguishes between 13 highly conserved IFN-α subtypes and found that reovirus T3D induces five IFN-α subtypes in primary cardiac myocyte and fibroblast cultures: IFN-α1, -α2, -α4, -α5, and -α8/6. Murine IFN-α1, -α2, -α4, or -α5 treatment induced IRF7 and ISG56 and inhibited reovirus T3D replication in both cell types. This first investigation of IFN-α subtypes in cardiac cells for any virus demonstrates that IFN-α is induced in cardiac cells, that it is both subtype and cell type specific, and that it is likely important in the antiviral cardiac response.     

缬沙坦对大鼠心室肌细胞L-型钙通道电流的影响

目的研究AT1受体拮抗剂缬沙坦对正常大鼠心室肌细胞L-钙电流(Ica-L)的影响。方法采用全细胞膜片钳技术,观察0.4μmol/L的缬沙坦引起单个大鼠心室肌细胞L型钙通道电流变化。结果0.4μmol/L缬沙坦使正常大鼠心室肌细胞L型钙电流峰值明显降低(P<0.01),I-V曲线上移,但不改变其激活电位、峰值电位和反转电位。不影响通道稳态激活曲线,使稳态失活曲线左移。结论0.4μmol/L缬沙坦可直接阻断大鼠心室肌细胞L型钙通道,改变心室肌细胞的电生理特性,可能是其抗心律失常的机制之一。     

Interactions between calcium waves and action potential-induced calcium transients in guinea pig myocytes

Summary In isolated cardiac muscle, spontaneous Ca²⁺ release from the sarcoplasmic reticulum (SR) occurs and is propagated as a wave by a regenerative Ca²⁺-induced Ca²⁺ release mechanism. We have already reported that this wave is followed by a refractory period. The aim of this study is to investigate whether such a refractory period could also inactivate Ca²⁺ release from the SR triggered by an action potential. Myocytes were enzymatically isolated from guinea pig ventricles and loaded with acetoxymethylester form of fura-2 (fura-2 AM). The membrane potential was recorded with a conventional microelectrode technique, and spatio-temporal changes in fura-2 fluorescence were recorded using a digital TV system. After perfusion with potassium-free Tyrode solution, interactions between fluorescence transients due to propagating waves and action potential-induced fluorescence transients were observed. In this study, the action potentialinduced fluorescence transients could be detected in the next video frame after the propagation of the waves and showed gradual restitution of the transients. In addition, the sum of the fluorescence transients triggered by an action potential and the fluorescence transients due to the waves did not show significant change whenever the preceding waves were propagating. These results show that the interaction between the action potential-induced Ca²⁺ release and the calcium wave-induced Ca²⁺ release from the SR have the following characteristics: (1) For the action potentialinduced Ca²⁺ release, no absolute refractory period was observed 33 msec after the calcium wave. This suggests that the calcium waves can be reset by the action potential. (2) Regardless of whether the two release mechanisms are different, both share a common compartment of Ca²⁺ storage.     

Effects of β2-Adrenergic Antagonist on Cytosolic Ca^2＋ in Ventricular Myocytes from Infarcted Rat Heart

Objectives To investigate the effects ofβ2-adrenergic antagonist on cytosolic Ca2 ([Ca2 ]i) in ventricular myocytes from infarcted rat heart. Methods A ligature was placed around left anterior descending coronary artery of rat hearts. Rats in the control group were sham-operated. Cardiomyocytes were dissociated at two, four, eight weeks after myocardial infarction (MI) and [Ca2 ]i was measured via fura-2 fluorescence. The response of cardiomyocytes to isoproterenol in presence or absence of betal-adrenergic antagonist atenolol, beta2-adrenergic antagonist ICI118, 551 or non-selectiveβ1, 2- adrenergic antagonists propranolol was examined. Results The followings were found that ICI118, 551 had no significant effects on the rise of [Ca2 ]i induced by isoproterenol in normal ventricular myocytes (P > 0.05 ), ICI118, 551 only significantly attenuated the rise of [Ca2 ]i induced by isoproterenol at four weeks and eight weeks after MI (24.5%±5.7% vs 57.8%±13.2%, P<0.01; 12.2%±7.9% vs 44.6%±11.3%, P< 0.01). Atenolol had suppressive effects only in the control group and the post-Mi group of two weeks (P< 0.05 ) , and propranolol had suppressive effects in the control and all the three post-Mi groups (P < 0.01). Conclusions Beta2-adrenergic antagonist ICI118, 551 may exert negative effects on Ca2 overload initiated by sympathetic stimulation after MI.     

运动诱导的大鼠心肌细胞HSP72 mRNA表达与超微结构改变

目的 :研究运动诱导的大鼠心肌细胞HSP72mRNA表达与大鼠心肌细胞超微结构改变的可能关系。方法 :将 36只SD大鼠随机分为安静对照组 (C)、1周运动组 (T1)、2周运动组 (T2 )和3周运动组 (T3)。安静对照组不运动 ,T1组、T2组和T3组以 75 %VO2 max强度进行跑台运动 ,分别运动 1周、2周、3周 ,每周运动 6天 ,每天 1小时。在末次运动结束后 2 4小时以RT -PCR法检测大鼠心肌细胞热休克蛋白 72mRNA的表达 ;以常规电镜检测观察大鼠心肌细胞超微结构的变化。结果 :①T1和T2组HSP72mRNA表达明显多于C组和T3组。②以C组心肌细胞电镜表现为正常 ,则各组大鼠电镜表现的心肌损伤程度为T1组 >T2组 >T3组。结果提示 :运动不同时期造成心肌损伤程度不同的原因可能与运动后心肌细胞HSP72mRNA表达量不同有关。HSP72mRNA表达可能为运动后心肌保护的分子机理。