Study in calcium in muscle by intracellular organelles

我们研究了细胞内细胞器对肌肉收缩功能和松弛机制的作用。肌细胞中至少有许多控制收缩和松弛的细胞器，如肌浆网(SR)、横管结构(T系统)、钙泵、钠/钙交换机制、钙通道、兰尼定受体、DHP受体等。为了证明这些细胞器的作用，我们把重点放在幸运这些细胞器的动物身上。典型的例子是海洋浮游生物Doliolum，它与T系统和SR结合在一起，表明细胞外钙对其收缩是必不可少的，通过电压门控钙通道进入肌肉的钙只通过Na/Ca交换机制排出，而不是通过钙泵系统，这表明SR对肌肉收缩和细胞质钙隔离不是必需的。另一方面，由于受到频繁刺激，Doliolum停止运动一段时间，表明一旦胞内钙超过一定水平，就需要很长时间才能排出和降低细胞内钙。因此，SR可以起到持续降低细胞顶端钙水平和微调细胞内钙水平的作用，而具有‘T’和SR细胞器的动物降低细胞内钙水平的Na/Ca交换活性有限，强烈提示通过发育T‘和SR细胞器来实现钙调控机制的转变。

We have investigated the role of the intracelluar organelles to the function of the muscle contractility and the relaxation mechanism. At least there are many organelles which control the contraction and relaxation in muscle cell such as sarcoplasmic reticulum (SR), transvers tubular structure (T system), Ca pump, Na/Ca exchange mechanism, Ca channel, ryanodine receptor, DHP receptor and so on. To testify the role of such organe lles, we focused on the animals lucking these organelles. The typical example is the marine plankton Doliolum, which lucking the T system and SR together, shows the essential necessity of extracellular Ca for its contraction and the Ca get in the muscle through voltage gated Ca channel is extruded only by the Na/Ca exchange mechanism not by Ca pumpinging system, suggesting that the SR is not essential for muscle contraction and cytoplasmic Ca sequestering. On the other hard, by frequent stimulation Doliolum stop its movement for a while, indicating once the cytoplasmic Ca exceeded thecertain level it took a long time to extrude and lower intacellular Ca. Thus SR could play a role of continuous lowering the cytop)lasmic Ca level and fine tuning of the intracellular Ca level, ON the other hand the animal with 'T and SR organelles the activity of Na/Ca exchange for lowering intracellular Ca level is limited, strongly suggesting the transition of Ca control mechanism by developing the T' and SR organelles.