Joint Study on Evolution of Skeletal Muscle E-C Coupling

高等脊椎动物骨骼肌兴奋-收缩偶联（E-C偶联）的一个显著特征，即收缩不需要Ca^2+内流。这是因为膜去极化直接触发肌浆网（SR）释放Ca^2+。负责横管（T-管）膜中的这种信号转导的分子是二氢吡啶（DHP）受体，其被认为负责电压传感器（潜在的E-C偶联）和L-型Ca^2+通道的双重功能。在无脊椎动物肌纤维的E-C偶联中，外部Ca^<2+>内流是收缩所必需的，并且存在DHP -受体，但仅负责L型Ca^<2+>通道功能。因此，高等脊椎动物的E-C偶联机制与无脊椎动物的E-C偶联机制有质的不同。去极化诱导Ca^2+释放的新机制的获得一定经历了一个进化的过程。主被摄体 关于我们 本研究的目的是对代表动物进化不同阶段的物种进行研究，并比较E-C偶联的生物物理和形态特征，我们报道了文昌鱼（Branchiostoma lanceolatum）和七鳃鳗（Lampetra planeri）之间的进化步骤可能发生在较低的脊索动物中。对单个快肌纤维进行的全细胞电压钳实验表明，这种进化性变化伴随着膜内电荷运动成分的出现，这一成分可被硝苯地平（一种DHP衍生物）阻断，并伴随着Ca^2+通道激活动力学的显著减慢。在七鳃鳗、小鼠和角鲨的纤维中，细胞内Ca^2+释放（用Ca^2+敏感的荧光染料fluo 3测定）与膜去极化有关，对外部施加的Co^2+具有抵抗性，并被硝苯地平抑制。相比之下，在文昌鱼纤维中，Co^<2+>抑制Ca^<2 +>-释放。这些结果有力地支持了硝苯地平敏感的膜内电荷运动是脊椎动物骨骼肌E-C偶联的信号传导机制的假设，海洋无脊椎动物和低等脊椎动物代表了一个独特的基因库，为我们提供了有关DHP受体分子进化的年代学证据。少

A distinctive feature of the excitation-contraction coupling (E-C coupling) of skeletal muscle in higher vertebrates in that Ca^<2+> -influx is not necessary for contraction. This is because membrane depolarisation directly triggers Ca^<2+> release from the sarcoplasmic reticulum (SR). The molecule responsible for this signal transduction in the transverse tubular (T-tubular) membrane is a dihydropyridine (DHP) receptor, which is thought to be responsible for the dual function, of voltage sensor (underlying E-C coupling) and the L-type Ca^<2+> channel. In E-C coupling in invertebrate muscle fibers, influx of external Ca^<2+> is necessary for contraction, and a DHP -receptor is present, but responsible for only the L-type Ca^<2+> channel function. Therefore, the E-C coupling mechanism in higher vertebrates is qualitativele different from that in invertebrates. There must have been an evolutionary step to acquire the novel depolarisation-induced Ca^<2+> release mechanism. The main object … More ive of the present research project is to examine species representing different stages in animal evolution, and compare the biophysical and morphological properties of E-C coupling.We reported that the evolutionry step might have occurred in lower chordates between amphioxus (Branchiostoma lanceolatum) and lamprey (Lampetra planeri). Whole-cell voltage clamp experiments on single fast muscle fibers suggest that this evolutionary change is accompanied by the appearance of a component of intramembrane charge movement, which is blocked by nifedipine, a DHP derivative, and by a remarkable slowing-down of the activation kinetics of the Ca^<2+> channel. In the fibers of lamprey, mouse, and dogfish, intracellular Ca^<2+>-release (measured using the Ca^<2+> sensitive flurescence dye fluo3) is associated with membrane depolarisation, is resistant to externally applied Co^<2+>, and is suppressed by nifedipine. In contrast, in the amphioxus fiber, Ca^<2+>-release is suppressed by Co^<2+>. The results strongly support the hypothesis that nifedipine-sensitive intramembrane charge movement is the signal tansduction mechanism of vertebrate skeletal muscle E-C coupling.Marine invertebrates and lower vertebrates represent a unique 'gene-bank' of such diverse material and should provide us with chronological evidence about the molecular evolution of the DHP-receptor. Less