Mukou Masao, Kishi Hirohiko, Shirakawa Ibuki, Kobayashi Takakazu, Tominaga Katsutoshi, Imanishi Haruka, Sugi Haruo
Department of Physiology, School of Medicine, Teikyo University, Itabashi-ku, Tokyo 173-8605, Japan.
J Exp Biol. 2004 Apr;207(Pt 10):1675-81. doi: 10.1242/jeb.00934.
The anterior byssal retractor muscle (ABRM) of the bivalve Mytilus edulis shows a prolonged tonic contraction, called the catch state. To investigate the catch mechanism, details of which still remain obscure, we studied the mechanical responses of ABRM fibres to quick increases in load applied during maximum active isometric force (P(0)) generation and during the catch state. The mechanical response consisted of three components: (1) initial extension of the series elastic component (SEC), (2) early isotonic fibre lengthening with decreasing velocity, and (3) late steady isotonic fibre lengthening. The ABRM fibres could bear extremely large loads up to 10-15P(0) for more than 30-60 s, while being lengthened extremely slowly. If, on the other hand, quick increases in load were applied during the early isometric force development, the ABRM fibres were lengthened rapidly ('give') under loads of 1.5-2P(0). These findings might possibly be explained by two independent systems acting in parallel with each other; one is the actomyosin system producing active shortening and active force generation, while the other is the load-bearing system responsible for the extremely marked load-bearing ability as well as the maintenance of the catch state.
双壳贝类紫贻贝的前足丝牵缩肌（ABRM）呈现出一种持续的强直性收缩，称为捕捉状态。为了研究捕捉机制（其细节仍不清楚），我们研究了ABRM纤维在最大主动等长力（P(0)）产生期间和捕捉状态下对快速增加的负荷的机械反应。机械反应由三个部分组成：（1）串联弹性成分（SEC）的初始伸展，（2）早期等张纤维以递减速度延长，以及（3）后期稳定的等张纤维延长。ABRM纤维能够承受高达10 - 15P(0)的极大负荷超过30 - 60秒，同时延长极其缓慢。另一方面，如果在早期等长力发展期间快速增加负荷，ABRM纤维在1.5 - 2P(0)的负荷下会迅速延长（“屈服”）。这些发现可能由两个相互平行作用的独立系统来解释；一个是产生主动缩短和主动力的肌动球蛋白系统，另一个是负责极其显著的承重能力以及维持捕捉状态的承重系统。
