Birenheide R, Motokawa T
Tokyo Institute of Technology, Faculty of Bioscience & Biotechnology, Japan.
Biol Bull. 1996 Aug;191(1):1-4. doi: 10.2307/1543055.
Active movements in animals are usually attributed to cellular protein engines, e.g., the actin-myosin system of muscle cells. Here we report the first evidence of an extracellular contractile connective tissue, which we have found in sea lilies and feather stars (Echinodermata, Crinoida). These marine animals have arm muscles that are antagonized, not by other muscles, but by ligaments consisting of extracellular fibrils interspersed with neuron-like cell processes. Contractile cells are lacking, yet these arm ligaments actively contracted upon stimulation. The ligaments stayed in a contracted condition even after the stimulus had stopped. The stresses generated were lower than those of typical skeletal muscles. Additional data from crinoid cirri, which lack muscles entirely, corroborate the hypothesis that the connective tissue of the ligaments is contractile.
动物的主动运动通常归因于细胞蛋白引擎，例如肌肉细胞的肌动蛋白-肌球蛋白系统。在此，我们报告了一种细胞外收缩性结缔组织的首个证据，这是我们在海百合和海羽星（棘皮动物门，海百合纲）中发现的。这些海洋动物的臂部肌肉的拮抗作用并非由其他肌肉完成，而是由韧带完成，这些韧带由散布着类神经元细胞突起的细胞外纤维构成。它们没有收缩细胞，但这些臂部韧带在受到刺激时会主动收缩。即使刺激停止后，韧带仍保持收缩状态。产生的应力低于典型骨骼肌的应力。来自完全没有肌肉的海百合触须的其他数据证实了韧带的结缔组织具有收缩性这一假说。
