Department of Physiology, Teikyo University School of Medicine, Tokyo 173-8605, Japan.
Department of Sports Medicine, Teikyo Heisei University, Chibaken 290-0193, Japan.
Int J Mol Sci. 2020 Oct 14;21(20):7576. doi: 10.3390/ijms21207576.
Molluscan smooth muscles exhibit the catch state, in which both tension and resistance to stretch are maintained with very low rates of energy consumption. The catch state is studied mainly on the anterior byssus retractor muscle (ABRM) of a bivalve molluscan animal, which can easily be split into small bundles consisting of parallel fibers. The ABRM contracts actively with an increase in the intracellular free Ca ion concentration, [Ca]i, as with all other types of muscle. Meanwhile, the catch state is established after the reduction of [Ca]i to the resting level. Despite extensive studies, the mechanism underlying the catch state is not yet fully understood. This article briefly deals with (1) anatomical and ultrastructural aspects of the ABRM, (2) mechanical studies on the transition from the active to the catch state in the isotonic condition, (3) electron microscopic and histochemical studies on the intracellular translocation of Ca ions during the transition from the active to the catch state, and (4) biochemical studies on the catch state, with special reference to a high molecular mass protein, twitchin, which is known to occur in molluscan catch muscles.
软体动物平滑肌表现出“捕获状态”，此时张力和抗拉伸阻力都能以非常低的能量消耗率维持。捕获状态主要在双壳类软体动物的前闭壳肌（ABRM）上进行研究，该肌肉很容易分裂成由平行纤维组成的小束。与所有其他类型的肌肉一样，ABRM 在细胞内游离 Ca 离子浓度 [Ca]i 增加时会主动收缩。同时，在 [Ca]i 降低到静息水平后，捕获状态会建立。尽管进行了广泛的研究，但捕获状态的机制尚未完全理解。本文简要涉及：（1）ABRM 的解剖学和超微结构方面；（2）在等张条件下从主动状态向捕获状态过渡的力学研究；（3）在从主动状态向捕获状态过渡过程中细胞内 Ca 离子转移的电子显微镜和组织化学研究；（4）捕获状态的生化研究，特别提到了一种已知存在于软体动物捕获肌肉中的高分子质量蛋白，即 twitchin。
