Kubalova Zuzana, Györke Inna, Terentyeva Radmila, Viatchenko-Karpinski Serge, Terentyev Dmitry, Williams Simon C, Györke Sandor
Texas Tech University HSC, Lubbock, USA.
J Physiol. 2004 Dec 1;561(Pt 2):515-24. doi: 10.1113/jphysiol.2004.073940. Epub 2004 Oct 14.
Waves of Ca2+-induced Ca2+ release occur in various cell types and are involved in the pathology of certain forms of cardiac arrhythmia. These arrhythmias include catecholaminergic polymorphic ventricular tachycardia (CPVT), certain cases of which are associated with mutations in the cardiac calsequestrin gene (CASQ2). To explore the mechanisms of Ca2+ wave generation and unravel the underlying causes of CPVT, we investigated the effects of adenoviral-mediated changes in CASQ2 protein levels on the properties of cytosolic and sarcoplasmic reticulum (SR) Ca2+ waves in permeabilized rat ventricular myocytes. The free [Ca2+] inside the sarcoplasmic reticulum ([Ca2+]SR) was monitored by fluo-5N entrapped into the SR, and cytosolic Ca2+ was imaged using fluo-3. Overexpression of CASQ2 resulted in significant increases in the amplitude of Ca2+ waves and interwave intervals, whereas reduced CASQ2 levels caused drastic reductions in the amplitude and period of Ca2+ waves. CASQ2 abundance had no impact on resting diastolic [Ca2+]SR or on the amplitude of the [Ca2+]SR depletion signal during the Ca2+ wave. However, the recovery dynamics of [Ca2+]SR following Ca2+ release were dramatically altered as the rate of [Ca2+]SR recovery increased approximately 3-fold in CASQ2-overexpressing myocytes and decreased to 30% of control in CASQ2-underexpressing myocytes. There was a direct linear relationship between Ca2+ wave period and the half-time of basal [Ca2+]SR recovery following Ca2+ release. Loading the SR with the low affinity exogenous Ca2+ buffer citrate exerted effects quantitatively similar to those observed on overexpressing CASQ2. We conclude that free intra-SR [Ca2+] is a critical determinant of cardiac Ca2+ wave generation. Our data indicate that reduced intra-SR Ca2+ binding activity promotes the generation of Ca2+ waves by accelerating the dynamics of attaining a threshold free [Ca2+]SR required for Ca2+ wave initiation, potentially accounting for arrhythmogenesis in CPVT linked to mutations in CASQ2.
钙离子诱导的钙离子释放波出现在多种细胞类型中，并参与某些形式的心律失常的病理过程。这些心律失常包括儿茶酚胺能多形性室性心动过速（CPVT），其中某些病例与心脏隐钙素基因（CASQ2）的突变有关。为了探究钙离子波产生的机制并揭示CPVT的潜在病因，我们研究了腺病毒介导的CASQ2蛋白水平变化对通透化大鼠心室肌细胞中胞质和肌浆网（SR）钙离子波特性的影响。通过包埋在肌浆网中的fluo-5N监测肌浆网内的游离钙离子浓度（[Ca2+]SR），并使用fluo-3对胞质钙离子进行成像。CASQ2的过表达导致钙离子波的幅度和波间间隔显著增加，而CASQ2水平降低则导致钙离子波的幅度和周期急剧减小。CASQ2的丰度对静息舒张期的[Ca2+]SR或钙离子波期间[Ca2+]SR耗竭信号的幅度没有影响。然而，钙离子释放后[Ca2+]SR的恢复动力学发生了显著改变，因为在过表达CASQ2的肌细胞中[Ca2+]SR的恢复速率增加了约3倍，而在低表达CASQ2的肌细胞中则降至对照的30%。钙离子波周期与钙离子释放后基础[Ca2+]SR恢复的半衰期之间存在直接的线性关系。用低亲和力的外源钙离子缓冲剂柠檬酸盐加载肌浆网所产生的效应在数量上与过表达CASQ2时观察到的效应相似。我们得出结论，肌浆网内的游离钙离子是心脏钙离子波产生的关键决定因素。我们的数据表明，肌浆网内钙离子结合活性的降低通过加速达到钙离子波起始所需的阈值游离[Ca2+]SR的动力学来促进钙离子波的产生，这可能是与CASQ2突变相关的CPVT心律失常发生的原因。
