心肌细胞钙稳态失调在心力衰竭中作用的研究进展

心肌细胞的钙稳态依赖于质膜、肌/内质网(SR)、线粒体等对钙(Ca2+)转运的调节.胞质钙超载、SR钙渗漏等在内的钙稳态失调,使心肌细胞钙瞬变减低,收缩力下降是心力衰竭的主要特征之一.     

Ryanodine受体2基因沉默对大鼠心肌细胞缺血再灌注损伤的影响

目的 观察应用RNA干扰阻断Ryanodine受体2(RyR2)合成是否对心肌缺血再灌注(I/R)损伤有保护作用.方法 分离培养大鼠原代心肌细胞并建立I/R模型.应用RNA干扰技术阻断RyR2表达,分别检测对照组、RNA干扰组、I/R模型组、RNA干扰+IYR模型组细胞凋亡率、RyR2 mRNA、细胞内钙离子浓度、培养上清中乳酸脱氢酶(LDH)水平和线粒体膜电位变化.结果 与对照组相比.I/R组细胞发生明显凋亡和损伤(60.1%比5.5%.P<0.05),细胞内钙离子浓度显著上升(平均荧光强度21.2比7.6,P<0.05),RyR2表达变化不明显(20.1比22.7,P>0.05),线粒体膜电位显著下降(平均荧光强度37.2比85.1,P<0.05).相对于I/R组,siRNA干预组细胞RyR2表达显著下降(6.8比20.1,P<0.05),LDH水平、凋亡率、细胞内钙离子浓度均有明显下降(上清LDH为48 IU/L比125 IU/L,Annexin V阳性细胞31.2%比60.1%,钙离子浓度为平均荧光强度8.6比21.2,均P<0.05),线粒体膜电位显著升高(55.8比37.2,P<0.05).结论 在大鼠原代心肌细胞中RyR2基因沉默对心肌I/R损伤有一定保护作用.     

钙诱导钙释放机制与慢性心力衰竭的关系

目的:探讨钙诱导的钙释放(CICR)过程与慢性心力衰竭之间的关系.方法:采用冠状动脉左前降支结扎手术制作大鼠慢性心衰模型,酶解法分离成年大鼠心室肌细胞,然后使用NiCl2(5mmol/L)和毒胡萝卜素(TG, 100nmol/L)分别阻断钠钙交换体和钙泵,采用膜片钳和激光扫描共聚焦显微镜同步实时系统记录心肌细胞的L-型钙电流(ICa.L)以及CICR过程中的钙瞬变.结果:心衰大鼠心肌细胞的ICa.L低于正常大鼠心肌细胞的ICa.L;心衰组心肌细胞内CICR过程中的钙火花发生率低于正常对照组.结论:心肌细胞CICR功能的异常与心力衰竭的发生机制有着十分密切的关系,可能为导致心力衰竭发生的重要原因之一.     

钙敏感受体在缺氧-复氧诱导的大鼠心肌细胞凋亡中的作用

目的： 观察大鼠心肌钙敏感受体(CaSR) 在心肌缺氧/再灌注损伤时的表达情况及其介导的细胞内钙变化，以及其参与细胞凋亡的相关信号转导途径。方法： Lagendorff离体灌流方法复制心脏缺氧-复氧（anoxia-reoxygenation，A/R）模型；观察缺氧/再灌注及加入CaSR激动剂时CaSR的表达；应用激光扫描共聚焦显微镜（LSCM）观察大鼠心肌细胞正常、缺氧、缺氧/再灌注时［Ca2+］i变化；HE染色观察细胞形态学改变；TUNEL染色观察细胞凋亡； Western blotting检测心肌组织胞浆中caspase 3、caspase 9 的表达。结果： 心肌A/R组及加入CaSR激动剂时CaSR的表达明显增高，细胞内钙明显升高。HE染色发现A/R组和激动剂组损伤明显，TUNEL显示2组凋亡细胞大量存在。同时，A/R组和激动剂组胞浆中caspase 3和caspase 9的表达增加。结论： CaSR参与大鼠心肌A/R损伤时细胞内钙超载的形成，并促进A/R损伤时心肌细胞凋亡。     

Ryanodine受体2增快胚胎发育期心肌细胞胞浆内钙瞬变

目的 :在成年心肌细胞中 ,细胞内钙瞬变是由外钙内流激发肌浆网储存钙的释放而引起的 ,位于肌浆网的钙离子释放通道ryanodine受体 2 (RyR2 )在其中起着关键的调控作用。但RyR2在发育早期心肌细胞钙瞬变形成中的作用和地位仍不清楚。本课题利用RyR2基因剔除 (RyR2 -/-)胚胎干细胞 (embryonicstemcell,ESC)体外分化的心肌细胞 ,探讨了RyR2在心肌发育过程中对钙瞬变的调控作用。方法 :在体外诱导正常R1系ESC (RyR2 + /+ )和RyR2 -/-ESC分化为心肌细胞 ,并分离出能自主收缩的心肌细胞 ,以钙离子荧光指示剂Indo - 1为探针 ,应用光谱荧…     

参仙升脉口服液通过兰尼碱受体2(RyR2)调控病态窦房结综合征小鼠钙转运

目的 探索参仙升脉口服液对窦房结功能障碍小鼠钙离子转运的影响及可能机制.方法 C57B6小鼠随机分为假手术组(Sham组)、窦房结综合征组(SSS组)和参仙升脉口服液治疗组(SXSM组);通过Alzet渗透压泵泵入ANGII的方法建立SSS小鼠模型.各组小鼠进行心率检测;IF方法检测钙离子浓度;Western blot...     

三磷酸肌醇影响钙释放的两个作用

此模型主要说明激动剂诱发的Ca2+振荡实验中影响Ca2+释放的两个因素(a)三磷酸肌醇(IP3)抑制Ca2+从内质网ER中释放.(b)IP3通过Gq作用磷酸酶C促使Ca2+从ER释放.模型假设ER上IP3受体是相互独立的亚基组成的四聚物,每个亚基可以结合Ca2+和IP3.IP3受体/Ca2+通道的缓慢恢复到稳定状态是钙对自身释放抑制的原因.钙振荡的关键是最大Ca2+依赖性IP3的进入速率(v6)和IP3的衰减时间常数(v7)的比值Ⅰ当v6/v7<0.28,不振荡;II当0.28<v6/v7<0.572振荡;III当v6/v7>0.572由振荡状态快速恢复到稳定状态.     

心肌细胞收缩期钙瞬变的调节机制的研究进展

心肌细胞收缩是由细胞内游离钙浓度([Ca^2 ]i)收缩期增高引起的。[Ca^2 ]i增高的多少是心肌收缩力量和心输出量的主要调节机制。而胞浆收缩Ca^2 主要来自于胞外钙内流和肌浆网(sacroplasmic reticulum，SR)的钙释放。本介绍心肌细胞收缩胞浆Ca^2 浓度升高的机制与部分调节因素的分子研究进展。     

钙／钙调素依赖的蛋白激酶Ⅱ对心肌细胞钙循环的影响

在心衰、心肌肥厚和心肌缺血等情况下,心肌细胞钙离子循环常出现障碍,导致心脏电-机械活动异常,临床发现心律失常和心源性猝死常和钙循环异常有关.钙调素和钙/钙调素依赖的蛋白激酶Ⅱ(CaMKII)通过调节钙循环的各个环节来影响心肌细胞信号传导和兴奋-收缩偶联,在心衰或心肌肥厚等病理条件下细胞内表达升高.对其深入研究有利于了解这些病理情况下心律失常发生的机制.     

钙/钙调素依赖的蛋白激酶II对心肌细胞钙循环的影响

在心衰、心肌肥厚和心肌缺血等情况下 ,心肌细胞钙离子循环常出现障碍 ,导致心脏电 机械活动异常 ,临床发现心律失常和心源性猝死常和钙循环异常有关。钙调素和钙 /钙调素依赖的蛋白激酶II(CaMKII)通过调节钙循环的各个环节来影响心肌细胞信号传导和兴奋 收缩偶联 ,在心衰或心肌肥厚等病理条件下细胞内表达升高。对其深入研究有利于了解这些病理情况下心律失常发生的机制。     

Involvement of Ca2+-induced Ca2+ release in the biphasic Ca2+ response evoked by readdition of Ca2+ to the medium after UTP-induced store depletion in A431 cells

 We have recently shown that the Ca²⁺ response in endothelial cells evoked by readdition of Ca²⁺ to the medium after store depletion caused by a submaximal concentration of agonist can involve Ca²⁺ release from Ca²⁺ stores sensitive to both inositol 1,4,5-trisphosphate and ryanodine. The present experiments were performed to determine whether this mechanism might also exist in other types of cell. For this purpose, we used the human carcinoma cell line A431, which has a varied resting [Ca²⁺]_i. We found that the amplitude of the Ca²⁺ response evoked by Ca²⁺ readdition did not correlate with the amplitude of the preceding UTP-evoked Ca²⁺ release, but did positively correlate with the initial [Ca²⁺]_i. An inspection of the two patterns of response seen in this study (the large biphasic and small plateau-shaped Ca²⁺ responses) revealed that there is an accelerating rise in [Ca²⁺]_i during the biphasic response. Application of ryanodine during the plateau-shaped Ca²⁺ response reversibly transformed it into the biphasic type. Unlike ryanodine, caffeine did not itself evoke Ca²⁺ release, but it caused a further [Ca²⁺]_i rise when [Ca²⁺]_i had already been elevated by thapsigargin. These data suggest that in A431 cells, as in endothelial cells, the readdition of Ca²⁺ after agonist-evoked store depletion can evoke Ca²⁺-induced Ca²⁺ release. This indicates that Ca²⁺ entry may be overestimated by this widely used protocol. Received: 28 July 1997 / Received after revision: 25 November 1997 / Accepted: 26 November 1997     

Effect of chloride on Ca2+ release from the sarcoplasmic reticulum of mechanically skinned skeletal muscle fibres

 The effect of intracellular Cl^– on Ca²⁺ release in mechanically skinned fibres of rat extensor digitorum longus (EDL) and toad iliofibularis muscles was examined under physiological conditions of myoplasmic [Mg²⁺] and [ATP] and sarcoplasmic reticulum (SR) Ca²⁺ loading. Both in rat and toad fibres, the presence of 20 mM Cl^–in the myoplasm increased Ca²⁺ leakage from the SR at pCa (i.e. –log₁₀ [Ca²⁺]) 6.7, but not at pCa 8. Ca²⁺ uptake was not significantly affected by the presence of Cl^–. This Ca²⁺-dependent effect of Cl^– on Ca²⁺ leakage was most likely due to a direct action on the ryanodine receptor/Ca²⁺ release channel, and could influence channel sensitivity and the resting [Ca²⁺] in muscle fibres in vivo. In contrast to this effect, acute addition of 20 mM Cl^– to the myoplasm caused a 40–50% reduction in Ca²⁺ release in response to a low caffeine concentration both in toad and rat fibres. One possible explanation for this latter effect is that the addition of Cl^– induces a potential across the SR (lumen negative) which might reduce Ca²⁺ release via several different mechanisms. Received: 20 October 1997 / Received after revision: 1 December 1997 / Accepted: 2 December 1997     

Effect of calmodulin on Ca2+-induced Ca2+ release of skeletal muscle from mutant mice expressing either ryanodine receptor type 1 or type 3

 We analyzed the effects of calmodulin (CaM) on Ca²⁺-induced Ca²⁺ release (CICR) in mouse skeletal muscle cells expressing only ryanodine receptor type 1 (RyR-1) or type 3 (RyR-3) following targeted disruption of one of the RyR genes. Under Mg²⁺-free conditions, CaM potentiated CICR via RyR-3 at low Ca²⁺ concentrations (pCa≥6) but inhibited CICR at high Ca²⁺ concentrations (pCa≤5). On the other hand, CaM potentiated CICR via RyR-1 between pCa 7 and pCa 5. Greater concentrations of CaM were required for potentiation of CICR at pCa 6 than for the inhibition at pCa 5 in the RyR-3-expressing cells. Similarly, higher concentrations of CaM were required for the potentiation of CICR via RyR-1 at pCa 6 than potentiation at pCa 5. In the presence of Mg²⁺ and β,γ-methyleneadenosine 5′-trisphosphate (AMPOPCP), the same differential effects of CaM on the CICR via the different subtypes of RyR were observed. These data suggest that multiple CaM-binding sites are involved in the differential effects on RyR-1 and RyR-3. These effects of CaM are important for the evaluation of the physiological roles of RyRs. Received: 5 May 1998 / Received after revision: 14 August 1998 / Accepted: 3 September 1998     

Inhibitory action of Ca2+ on spontaneous transmitter release at motor nerve terminals in a high K+ solution

The inhibitory effect of a high external Ca²⁺ ([Ca²⁺]_o) on spontaneous transmitter release in a high K⁺ solution (Gage and Quastel 1966; Birks et al. 1968) was studied at the frog neuromuscular junction, based on the hypothesis that an increased intracellular free Ca²⁺ ([Ca²⁺]_i) in the nerve terminal plays a key role in the depression. Three procedures were employed to increase [Ca²⁺]_i; increasing [Ca²⁺]_o, application of caffeine and tetanic nerve stimulation. All of these procedures increased m.e.p.p. frequency in normal Ringer. However, as the basic m.e.p.p. frequency was increased by raising the external K⁺ concentration (7–15 mM), their facilitatory effects on m.e.p.p. frequency decreased, disappeared and eventually reversed to depressant actions. Since a rise in the external K⁺ concentration would increase the steady state level of [Ca²⁺]_i, it is suggested that when the [Ca²⁺]_i is preset at a high level, manipulations so as to further increase [Ca²⁺]_i depress spontaneous release of transmitter. Possible mechanisms for this inhibition was discussed in relation to a question whether or not the rate of spontaneous transmitter release is a monotonic function of [Ca²⁺]_i.     

卡维地洛对RyR2介导的自发性钙振荡的抑制作用

 目的：探讨并比较卡维地洛和其它β受体阻滞剂对兰尼定受体2（RyR2）介导的自发性钙振荡的抑制作用。方法：采用Flp-In T-REx Core Kit构建可以稳定诱导表达RyR2的HEK293细胞株,采用酶解方法分离大鼠单个心肌细胞。逐步提高细胞外钙离子浓度,诱发细胞自发性钙振荡。单细胞钙影像技术记录并检测卡维地洛等β受体阻滞剂对HEK293细胞株及心肌细胞自发性钙振荡的作用。结果：卡维地洛30 μmol/L可明显抑制心肌细胞和表达RyR2的HEK293细胞株的自发性钙振荡,其抑制率分别为(6530±230)%和(6908±530)%;而美托洛尔、索他洛尔、阿替洛尔等常用的14种β受体阻滞剂对心肌细胞及HEK293细胞株的自发性钙振荡均无明显作用。结论：卡维地洛是唯一可以抑制RyR2介导的自发性钙释放的β受体阻滞剂,这可能是卡维地洛在降低心衰死亡率上优于其它β受体阻滞剂的机制之一。     

[Ca2+]i elevation evoked by Ca2+ readdition to the medium after agonist-induced Ca2+ release can involve both IP 3-, and ryanodine-sensitive Ca2+ release

 Sustained Ca²⁺ elevation (”Ca²⁺ response”), caused by subsequent readdition of Ca²⁺ to the medium after application of adenosine 5’-triphosphate (ATP, 15 μM) in a Ca²⁺-free medium, was studied using single bovine aortic endothelial (BAE) cells. In cells in which the resting intracellular Ca²⁺ concentration ([Ca²⁺]_i) was between about 50 and 110 nM, a massive Ca²⁺ response occurred and consisted of phasic and sustained components, whereas cells with a resting [Ca²⁺]_i of over 110 nM displayed small plateau-like Ca²⁺ responses. An increase of internal store depletion resulted in loss of the phasic component. When the store was partly depleted, the dependence of the Ca²⁺ response amplitude on resting [Ca²⁺]_i was biphasic over the range of 50 to 110 nM. The greatest degree of store depletion was associated with small monophasic Ca²⁺ responses, the amplitudes of which were almost constant and in the same range as resting [Ca²⁺]_i. Ni²⁺, known to partly block Ca²⁺ entry, caused no change in the half-decay time of [Ca²⁺]_i down to the level of the sustained phase [57 ± 4 s in control and 54 ± 3 s (n = 13) in the presence of 10 mM Ni²⁺] when added at the peak of the phasic component of the Ca²⁺ response. However, it lowered the sustained phase of the Ca²⁺ response by 42%. When applied at the start of the readdition of Ca²⁺, Ni²⁺ blocked the phasic component of the Ca²⁺ response, there being a threefold decrease in the initial rate of [Ca²⁺]_i rise. In cells with a resting [Ca²⁺]_i of 75–80 nM, pre-treatment with ryanodine (10 μM) did not affect the peak amplitude of the Ca²⁺ response, but it did increase the level of the sustained component. In some cells, ryanodine caused an oscillatory Ca²⁺ response. In conclusion, partial depletion of the inositol 1,4,5-trisphosphate-(IP ₃-) sensitive store by a submaximal concentration of agonist (in Ca²⁺-free medium) was followed, on readdition of Ca²⁺, by Ca²⁺ entry, which appeared to trigger IP ₃-sensitive Ca²⁺ release (IICR) which, in turn, initiated Ca²⁺-sensitive Ca²⁺ release (CICR), thus resulting in a massive elevation of [Ca²⁺]_i. Received: 3 July 1996 / Received after revision and accepted: 9 September 1996     

Novel regulators of RyR Ca2+ release channels: insight into molecular changes in genetically-linked myopathies

There are many mutations in the ryanodine receptor (RyR) Ca²⁺ release channel that are implicated in skeletal muscle disorders and cardiac arrhythmias. More than 80 mutations in the skeletal RyR1 have been identified and linked to malignant hyperthermia, central core disease or multi-minicore disease, while more than 40 mutations in the cardiac RyR2 lead to ventricular arrhythmias and sudden cardiac death in patients with structurally normal hearts. These RyR mutations cause diverse changes in RyR activity which either excessively activate or block the channel in a manner that disrupts Ca²⁺ signalling in the muscle fibres. In a different myopathy, myotonic dystrophy (DM), a juvenile isoform of the skeletal RyR is preferentially expressed in adults. There are two regions of RyR1 that are variably spiced and developmentally regulated (ASI and ASII). The juvenile isoform (ASI (−)) is less active than the adult isoform (ASI(+)) and its over-expression in adults with DM may contribute to functional changes. Finally, mutations in an important regulator of the RyR, the Ca²⁺ binding protein calsequestrin (CSQ), have been linked to a disruption of Ca²⁺ homeostasis in cardiac myocytes that results in arrhythmias. We discuss evidence supporting the hypothesis that mutations in each of these situations alter protein/protein interactions within the RyR complex or between the RyR and its associated proteins. The disruption of these protein–protein interactions can lead either to excess Ca²⁺ release or reduced Ca²⁺ release and thus to abnormal Ca²⁺ homeostasis. Much of the evidence for disruption of protein–protein interactions has been provided by the actions of a group of novel RyR regulators, domain peptides with sequences that correspond to sequences within the RyR and which compete with the endogenous residues for their interaction sites.     

Differential sensitivity to perchlorate and caffeine of tetracaine-resistant Ca2+ release in frog skeletal muscle

In voltage clamped frog skeletal muscle fibres 0.2 mM tetracaine strongly suppresses Ca²⁺ release. After this treatment Ca²⁺ release flux lacks its characteristic initial peak and the remaining steady component is strongly reduced when compared with the control condition. We studied the effect of two agonists of Ca²⁺ release on these tetracaine treated fibres. 8 mM ClO ₄ ⁻ added after tetracaine potentiated release flux from 0.11 ± 0.03 mM s⁻¹ to 0.34 ± 0.07 mM s⁻¹ (n = 6) although without recovery of the peak at any test voltage. The voltage dependence of the increased release was shifted towards more negative potentials (approximately −10 mV). The effects of ClO ₄ ⁻ on charge movement under these conditions showed the previously described characteristic changes consisting in a left shift of its voltage dependence (approximately −9 mV) together with a slower kinetics, both at the ON and OFF transients. Caffeine at 0.5 mM in the presence of the same concentration of tetracaine failed to potentiate release flux independently of the test voltage applied. When the cut ends of the fibre were exposed to a 10 mM BAPTA intracellular solution, in the absence of tetracaine, the peak was progressively abolished. Under these conditions caffeine potentiated release restoring the peak (from 0.63 ± 0.12 mM s⁻¹ to 1.82 ± 0.23 mM s⁻¹) with no effect on charge movement. Taken together the present results suggest that tetracaine is blocking a Ca²⁺ sensitive component of release flux. It is speculated that the suppressed release includes a component that is dependent on Ca²⁺ and mainly mediated by the activation of the β ryanodine receptors (the RyR3 equivalent isoform). These receptors are located parajunctionally in the frog and are not interacting with the dihydropyridine receptor.     

Functional characterization of the Ca2+-gated Ca2+ release channel of vascular smooth muscle sarcoplasmic reticulum

The Ca²⁺-gated Ca²⁺ release channel of aortic sarcoplasmic reticulum (SR) was partially purified and reconstituted into planar lipid bilayers. Canine and porcine aorta microsomal protein fractions were solubilized in the detergent 3-[(3-cholamidopropyl)dimethylammonio]-1-propane sulphonate (CHAPS) in the presence and absence of ³[H]-ryanodine and centrifuged through linear sucrose gradients. A single ³[H]-ryanodine receptor peak with an apparent sedimentation coefficient of 30 s was obtained. Upon reconstitution into planar lipid bilayers, the unlabelled 30 s protein fraction induced the formation of a Ca²⁺- and monovalent-ion-conducting channel (110 pS in 100 mM Ca²⁺, 360 pS in 250 mM K⁺). The channel was activated by micromolar Ca²⁺, modulated by millimolar adenosine triphosphate, Mg²⁺ and the Ca²⁺-releasing drug caffeine, and inhibited by micromolar ruthenium red. Micro- to millimolar concentrations of the plant alkaloid ryanodine induced a permanently closed state of the channel. Our results suggest that smooth muscle SR contains a Ca²⁺-gated Ca²⁺ release pathway, with properties similar to those observed for the skeletal and cardiac ryanodine receptor/Ca²⁺ release channel complexes.     

Mechanisms responsible for quantal Ca2+ release from inositol trisphosphate-sensitive calcium stores

Activation of cells by hormones, growth factors or neurotransmitters leads to an increased production of inositol trisphosphate (InsP₃) and, after activation of the InsP₃ receptor (InsP₃R), to Ca²⁺ release from intracellular Ca²⁺ stores. The release of intracellular Ca²⁺ is characterised by a graded response when submaximal doses of agonists are used. The basic phenomenon, called “quantal Ca²⁺ release”, is that even the maintained presence of a submaximal dose of agonist or of InsP₃ for long time periods (up to 20 min) provokes only a partial release of Ca²⁺. This partial, or quantal, release phenomenon is due to the fact that the initially very rapid InsP₃-induced Ca²⁺ release eventually develops into a much slower release phase. Physiologically, quantal release allows the Ca²⁺ stores to function as increment detectors and to induce local Ca²⁺ responses. The basic mechanism for quantal release of Ca²⁺ is presently not known. Possible mechanisms to explain the quantal behaviour of InsP₃- induced Ca²⁺ release include the presence of InsP₃Rs with varying sensitivities for InsP₃, heterogeneous InsP₃R distribution, intrinsic inactivation of the InsP₃Rs, and regulation of the InsP₃Rs by Ca²⁺ store content. This article reviews critically the evidence for the various mechanisms and evaluates their functional importance. A Ca²⁺-mediated conformational change of the InsP₃R is most likely the key feature of the mechanism for quantal Ca²⁺ release, but the exact mode of operation remains unclear. It should also be pointed out that in intact cells more than one mechanism can be involved.