Age-associated changes in beta-adrenergic modulation on rat cardiac excitation-contraction coupling.

Previous studies have demonstrated that the ability of beta-adrenergic receptor (beta AR) stimulation to increase cardiac contractility declines with aging. In the present study, the control mechanisms of excitation-contraction (EC) coupling, including calcium current (ICa), cytosolic Ca2+ (Cai2+) transient and contraction in response to beta AR stimulation were investigated in ventricular myocytes isolated from rat hearts of a broad age range (2, 6-8, and 24 mo). While the baseline contractile performance and the Cai2+ transient did not differ markedly among cells from hearts of all age groups, the responses of the Cai2+ transient and contraction to beta-adrenergic stimulation by norepinephrine (NE) diminished with aging: the threshold concentration and the ED50 increased in rank order with aging; the maximum responses of contraction and Cai2+ transient decreased with aging. Furthermore, the efficacy of beta AR stimulation to increase ICa was significantly reduced with aging, and the diminished responses of the contraction and Cai2+ transient amplitudes to NE were proportional to the reductions in the ICa response. These findings suggest that the observed age-associated reduction in beta AR modulation of the cardiac contraction is, in part at least, due to a deficit in modulation of Cai2+, particularly the activity of L-type calcium channels.     

衰老骨骼肌中的兴奋—收缩偶联与MG29蛋白

背景:"兴奋-收缩偶联"是神经-肌肉功能的基本功能特点,在衰老过程中肌肉功能的衰退与肌细胞中的兴奋-收缩解偶联存在密切关系.近年来针对衰老肌细胞功能退化的研究有了许多新进展.目的:综述有关衰老肌细胞钙离子变化的机制以及MG29蛋白在钙离子及与兴奋-收缩偶联过程中的作用的有关文献,为进一步了解衰老骨骼肌功能退化的机制提供理论参考.方法:应用计算机检索CNKI期刊全文数据库(2000-01/2009-11)和PubMed数据库(2009-01/2009-12)与衰老肌细胞钙离子变化的机制以及MG29蛋白及兴奋-收缩偶联相关的文献,检索词分别为"兴奋-收缩偶联:肌组织;肌细胞;衰老;抗阻训练;MG29"和"excitation-contraction;muscle;muscle cell;senescence;resistance traininq;MG29".纳入和衰老肌细胞钙离子、兴奋-收缩偶联及MG29蛋白相关的研究,排除陈旧的、重复的以及缺乏可信度的文献.结果与结论:初步检索到中英文文献共43篇,根据本研究的纳入排除标准,排除9篇不符合标准的文献,最终纳入34篇文献进行分析.结果发现,许多研究已经证明MG29蛋白在肌细胞兴奋-收缩偶联中起着重要的作用,而随增龄MG29会出现明显减少的规律,推断其在肌组织衰老中可能扮演重要角色.更为重要的是,新近有研究者发现适宜的抗阻训练可以使肌组织中MG29表达量增加.     

Effects of mitoxantrone on excitation-contraction coupling in guinea pig ventricular myocytes

The mechanisms of the inotropic effect of mitoxantrone (MTO), a synthetic dihydroxyanthracenedione derivative with antineoplastic activity, was investigated in guinea pig ventricular myocytes using whole-cell patch-clamp methods combined with fura-2 fluorescence and cell-edge tracking techniques. In right ventricular papillary muscles, 30 microM MTO increased isometric force of contraction as well as action potential duration (APD) in a time-dependent manner. The force of contraction was increased approximately 3-fold within 4 h. This positive inotropic effect was accompanied by a prolongation of time to peak force and relaxation time. In current-clamped single myocytes treated with 30 microM MTO for 30 min, an increase of cell shortening by 77% and a prolongation of APD by 19% was observed. Peak amplitude of the intracellular Ca(2+) transients was also increased by 10%. The contribution of APD prolongation to the enhancement of cell shortening induced by MTO was assessed by clamping control myocytes with action potentials of various duration. Prolongation of APD(90) (ADP measured at 90% of repolarization) by 24% led to an increase of cell shortening by 13%. When the cells were clamped by an action potential with constant APD, MTO still caused an increase of cell shortening by 59% within 30 min. No increase of the peak intracellular Ca(2+) transients, however, was observed under this condition. We conclude that both the APD prolongation and a direct interaction with the contractile proteins contributed to the positive inotropic effect of MTO.     

Altered cardiac excitation-contraction coupling in mutant mice with familial hypertrophic cardiomyopathy

Excitation-contraction coupling in cardiac muscle of familial hypertrophic cardiomyopathy (FHC) remains poorly understood, despite the fact that the genetic alterations are well defined. We characterized calcium cycling and contractile activation in trabeculae from a mutant mouse model of FHC (Arg403Gln knockin, alpha-myosin heavy chain). Wild-type mice of the same strain and age ( approximately 20 weeks old) served as controls. During twitch contractions, peak intracellular Ca2+ ([Ca2+]i) was higher in mutant muscles than in the wild-type (P < 0.05), but force development was equivalent in the two groups. Ca2+ transient amplitude increased dramatically in both groups as stimulation rate increased from 0.2 to 4 Hz. Nevertheless, developed force fell at the higher stimulation rates in the mutants but not in controls (P < 0.05). The steady-state force-[Ca2+]i relationship was less steep in mutants (Hill coefficient, 2.94 +/- 0.27 vs. 5.28 +/- 0.64; P > 0.003), with no changes in the [Ca2+]i required for 50% activation or maximal Ca2+-activated force. Thus, calcium cycling and myofilament properties are both altered in FHC mutant mice: more Ca2+ is mobilized to generate force, but this does not suffice to maintain contractility at high stimulation rates.     

Effects of cocaine on excitation-contraction coupling of aortic smooth muscle from the ferret.

The mechanism by which cocaine alters vascular tone is not fully understood. We determined the effects of cocaine on excitation-contraction coupling of isolated ferret aorta. Cocaine in concentrations less than or equal to 10(-4) M caused a contractile response in a dose-dependent manner. The response of control muscle was significantly larger than that in muscle from ferrets pretreated with reserpine. Cocaine-induced contraction was not affected by endothelial factors, but was significantly inhibited by prazosin 10(-7) M pretreatment. The intracellular calcium [( Ca++]i), as measured with aequorin, rose in conjunction with cocaine-induced contraction. The degree of contraction generated by 10(-4) M cocaine decreased after higher concentrations of cocaine greater than or equal to 10(-3) M, while aequorin luminescence remained elevated above the levels before 10(-6) M cocaine. The dose-response relationships of norepinephrine and sympathetic nerve stimulation were enhanced by 10(-6) M cocaine in control muscles; this did not occur in muscles from reserpine pretreated ferrets. In conclusion, (a) cocaine in concentrations less than or equal to 10(-4) M caused vascular contraction presumably by its presynaptic action with consequent alpha-1 adrenoceptor activation and consequent [Ca++]i rise; (b) high concentrations of cocaine greater than or equal to 10(-3) M reduced muscle tone by decreasing the Ca++ sensitivity of the contractile proteins; and (c) supersensitivity to norepinephrine was mediated by cocaine's action on adrenergic nerve endings.     

Effects of lysophosphatidylcholine on electrophysiological properties and excitation-contraction coupling in isolated guinea pig ventricular myocytes.

Lysophosphoglyceride accumulation in ischemic myocardium has been implicated as a cause of arrhythmias. We examined the effects of lysophosphatidylcholine (LPC) in isolated guinea pig ventricular myocytes. In paced myocytes loaded with the Ca2+ indicator Indo-1-AM and studied at room temperature, 20 microM LPC caused an initial positive inotropic effect followed by spontaneous automaticity, a decline in active cell shortening, and progressive diastolic shortening (contracture) leading to cell death. These changes were accompanied by a progressive increase in cytosolic [Ca2+]i. In patch-clamped myocytes dialyzed internally with high EGTA concentrations, LPC caused membrane depolarization, shortening of the action potential duration, and abnormal automaticity as seen in multicellular preparations. Voltage clamp experiments revealed the appearance of a nonselective leak conductance without significant changes in the delayed rectifier K+ current, inward rectifier K+ current, L-type Ca2+ current, and T-type Ca2+ current. Pretreatment with 20 mM caffeine and [Ca2+]o-free solution did not prevent the leak current. In patch clamped myocytes loaded with 0.1 mM Fura-2 salt, the [Ca2+]i transient induced by either voltage clamps or brief caffeine exposure remained normal until the nonselective leak current developed. The Na(+)-Ca2+ exchange current elicited during caffeine-induced [Ca2+]i transients also did not appear to be altered by LPC. Qualitatively similar results were obtained in myocytes studied at 35 degrees C. The membrane detergent saponin (0.005% wt/wt) mimicked all of the effects of LPC. We conclude that under these experimental conditions the effects of LPC are most compatible with a detergent action causing membrane leakiness with resultant depolarization, [Ca2+]i overload, and contracture.     

Action of diltiazem on excitation-contraction coupling in bullfrog skeletal muscle fibers

In this study the calcium antagonist drug diltiazem was found to produce twitch potentiation, lower the mechanical threshold potential and block inward calcium currents in bullfrog skeletal muscle fibers. Under tonic conditions (stimulation either every 1 or 2 min) high concentrations of diltiazem were required to enhance twitch tension (ED50 = 249 microM) and block calcium currents (IC50 = 190 microM). In addition, 100 microM diltiazem lowered the mechanical threshold rheobase potential from -49.3 to -57.0 mV. At higher rates of stimulation, concentrations of diltiazem as low as 1 and 10 microM, which had no tonic action, were found to produce twitch potentiation and calcium channel block, respectively. Onset and washout of tonic and frequency-dependent actions of diltiazem on twitch and current amplitude occurred over a similar time course. It is proposed that the mechanical potentiation, as well as the calcium channel block produced by diltiazem, result from the interaction of diltiazem with the same or similar receptor site(s).     

骨骼肌三联管膜蛋白与兴奋收缩偶联

背景:骨骼肌的兴奋收缩偶联机制及快速、有效的兴奋收缩偶联直接决定了运动能力.三联管是骨骼肌中特有的结构,是兴奋收缩偶联的结构基础.位于三联管上的膜蛋白在三联管结构的发育、正常形态的维持和功能的发挥中均起着关键作用.目的:介绍三联管膜蛋白的研究进展,对双氢吡啶受体蛋白,兰诺定受体蛋白,MG29 蛋白,JP 蛋白,Calumin 与STIM1蛋白,隐钙素和TRIC 通道蛋白等的结构和功能进行了归纳总结.方法:电子检索中国学术期刊数据库CNKI、读秀学术搜索等中文数据库和Elsevier SD,Springer Link 等英文数据库,检索时间1980/2010,均为骨骼肌衰老与力量-速度关系的相关综述和实验研究.并分析骨骼肌力量-速度关系随年龄变化的规律,以及该变化对老龄肌肉产生的影响.结果与结论:共纳入骨骼肌兴奋收缩偶联机制和三联管膜蛋白的相关文献28 篇.归纳文献结论证明,位于骨骼肌三联管的双氢吡啶受体蛋白,兰诺定受体蛋白,MG29 蛋白,JP 蛋白,Calumin 与STIM1 蛋白,隐钙素和TRIC 通道蛋白在骨骼肌的兴奋收缩偶联过程中各司其职,对骨骼肌正常的功能的发挥起着不可或缺的作用.但目前对这些蛋白的认识明显不足,尚需深入研究.     

骨骼肌三联管膜蛋白与兴奋收缩偶联

背景：骨骼肌的兴奋收缩偶联机制及快速、有效的兴奋收缩偶联直接决定了运动能力。三联管是骨骼肌中特有的结构,是兴奋收缩偶联的结构基础。位于三联管上的膜蛋白在三联管结构的发育、正常形态的维持和功能的发挥中均起着关键作用。目的：介绍三联管膜蛋白的研究进展,对双氢吡啶受体蛋白,兰诺定受体蛋白,MG29蛋白,JP蛋白,Calumin与STIM1蛋白,隐钙素和TRIC通道蛋白等的结构和功能进行了归纳总结。方法：电子检索中国学术期刊数据库CNKI、读秀学术搜索等中文数据库和Elsevier SD,Springer Link等英文数据库,检索时间1980/2010,均为骨骼肌衰老与力量—速度关系的相关综述和实验研究。并分析骨骼肌力量—速度关系随年龄变化的规律,以及该变化对老龄肌肉产生的影响。结果与结论：共纳入骨骼肌兴奋收缩偶联机制和三联管膜蛋白的相关文献28篇。归纳文献结论证明,位于骨骼肌三联管的双氢吡啶受体蛋白,兰诺定受体蛋白,MG29蛋白,JP蛋白,Calumin与STIM1蛋白,隐钙素和TRIC通道蛋白在骨骼肌的兴奋收缩偶联过程中各司其职,对骨骼肌正常的功能的发挥起着不可或缺的作用。但目前对这些蛋白的认识明显不足,尚需深入研究。     

Effects of the administration of 2,3-butanedione monoxime during conventional cardiopulmonary resuscitation on ischaemic contracture and resuscitability in a pig model of out-of-hospital cardiac arrest

Aim of the studyIschaemic contracture compromises the haemodynamic effectiveness of cardiopulmonary resuscitation and resuscitability. 2,3-Butanedione monoxime (BDM) reduced ischaemic contracture by inhibiting actin-myosin crossbridge formation in an isolated heart model. We investigated the effects of BDM on ischaemic contracture and resuscitation outcomes in a pig model of out-of-hospital cardiac arrest (OHCA).MethodsAfter 15 min of untreated ventricular fibrillation, followed by 8 min of basic life support, 16 pigs were randomised to receive either 2 ml kg⁻¹ of BDM solution (25 g l⁻¹) or 2 ml kg⁻¹ of saline during advanced cardiac life support (ACLS).ResultsDuring the ACLS, the control group showed an increase in left ventricular (LV) wall thickness from 10.0 mm (10.0–10.8) to 13.0 mm (13.0–13.0) and a decrease in LV chamber area from 8.13 cm² (7.59–9.29) to 7.47 cm² (5.84–8.43). In contrast, the BDM group showed a decrease in the LV wall thickness from 10 mm (9.0–10.8) to 8.5 mm (7.0–9.8) and an increase in the LV chamber area from 9.86 cm² (7.22–12.39) to 12.15 cm² (8.02–14.40). Mixed model analyses of the LV wall thickness and LV chamber area revealed significant group effects and group-time interactions. Spontaneous circulation was restored in four (50%) animals in the control group and in eight (100%) animals in the BDM group (p = 0.077). All the resuscitated animals survived during an intensive care period of 4 h.ConclusionBDM administered during cardiopulmonary resuscitation reversed ischaemic contracture in a pig model of OHCA.     

Cellular mechanism underlying burn serum-generated bidirectional regulation of excitation-contraction coupling in isolated rat cardiomyocytes

Myocardial depressant factors have long been recognized to be present in burn serum (BS) and contribute to burn-generated cardiac contractile dysfunction. However, much of the cellular and molecular mechanism for its role in the development of the cardiac deficiency remains unknown. In this study, we investigated the effect of BS on myocardial contractility and Ca handling in single rat cardiomyocytes. The results revealed that BS (5% by volume) bidirectionally regulated cardiac excitation-contraction (EC) coupling. The action potential-elicited Ca transient and cell shortening were increased by 28.0% ± 9.7% and 34.7% ± 12.5% within 20 min after BS stimulation (the upregulation phase), but decreased by 20.5% ± 6.8% and 32.3% ± 5.1% at 60 min after BS stimulation (the downregulation phase). There was a 32.0% ± 5.8% reduction in sarcoplasmic reticulum (SR) Ca content at the downregulation phase, whereas no alteration was detected at the upregulation phase. The incidences of spontaneous Ca sparks and Ca waves were significantly increased after BS stimulation, no matter at the upregulation or downregulation phase. The hyperactive Ca sparks and Ca waves could be completely abolished by antioxidative treatment (vitamin A, 0.2 mM; and vitamin E, 1 mM) and partially reversed by NOS inhibitor L-NAME (100 μM), but not by blocking Ca influx with nifedipine (1 μM). With the normalization of Ca sparks, BS-induced alterations of action potential-elicited Ca transient and contractility were prevented by antioxidative therapy. Taken together, we propose that BS-associated bidirectional regulation of EC coupling is attributed largely to oxidative stress-induced hyperactivity of ryanodine receptors, increasing EC coupling through enhancing intracellular Ca release initially, but subsequently decreasing EC coupling by partially depleting SR Ca content through enhancement of Ca spark-mediated SR leak.     

Role of intracellular sodium in the regulation of intracellular calcium and contractility. Effects of DPI 201-106 on excitation-contraction coupling in human ventricular myocardium.

Experiments were performed to investigate the mechanism of action of DPI 201-106 on human heart muscle. In both control and myopathic muscles, DPI produced concentration-dependent increases in action potential duration, resting muscle tension, peak isometric tension, and duration of isometric tension. These changes were associated with increases in resting intracellular calcium and peak calcium transients as measured by aequorin. At higher concentrations of DPI, a second delayed Ca2+ transient (L') appeared. L' was inhibited by tetrodotoxin and ryanodine, suggesting that DPI acts at both the sarcolemma and the sarcoplasmic reticulum. DPI toxicity was manifested by after-glimmers and after-contractions reflecting a Ca2+-overload state: DPI effects were mimicked by veratridine, a Na+ channel agonist, and reversed by tetrodotoxin, yohimbine, and cadmium, Na+ channel antagonists. These results suggest that DPI acts primarily as a Na+ channel agonist. DPI may produce an increase in intracellular Ca2+ by increasing intracellular Na+ and altering Na+-Ca2+ exchange across the sarcolemma. DPI may also increase intracellular Ca2+ by directly altering sarcoplasmic reticulum Ca2+ handling.     

Transgenic expression of replication-restricted enteroviral genomes in heart muscle induces defective excitation-contraction coupling and dilated cardiomyopathy.

Numerous studies have implicated Coxsackievirus in acute and chronic heart failure. Although enteroviral nucleic acids have been detected in selected patients with dilated cardiomyopathy, the significance of such persistent nucleic acids is unknown. To investigate the mechanisms by which restricted viral replication with low level expression of Coxsackieviral proteins may be able to induce cardiomyopathy, we generated transgenic mice which express a replication-restricted full-length Coxsackievirus B3 (CVB3) cDNA mutant (CVB3DeltaVP0) in the heart driven by the cardiac myocyte-specific myosin light chain-2v (MLC-2v) promoter. CVB3DeltaVP0 was generated by mutating infectious CVB3 cDNA at the VP4/VP2 autocatalytic cleavage site from Asn-Ser to Lys-Ala. Cardiac-specific expression of this cDNA leads to synthesis of positive- and negative-strand viral RNA in the heart without formation of infectious viral progeny. Histopathologic analysis of transgenic hearts revealed typical morphologic features of myocardial interstitial fibrosis and in some cases degeneration of myocytes, thus resembling dilated cardiomyopathy in humans. There was also an increase in ventricular atrial natriuretic factor mRNA levels, demonstrating activation of the embryonic program of gene expression typical of ventricular hypertrophy and failure. Echocardiographic analysis demonstrated the presence of left ventricular dilation and decreased systolic function in the transgenic mice compared with wild-type littermates, evidenced by increased ventricular end-diastolic and end-systolic dimensions and decreased fractional shortening. Analysis of isolated myocytes from transgenic mice demonstrate that there is defective excitation-contraction coupling and a decrease in the magnitude of isolated cell shortening. These data demonstrate that restricted replication of enteroviral genomes in the heart can induce dilated cardiomyopathy with excitation-contraction coupling abnormalities similar to pressure overload models of dilated cardiomyopathy.