Reappraisal of the connective-tissue catch hypothesis in echinoderms.

捕获器（CA）是一种胶原韧带，围绕着海胆每个脊柱底部的关节。作为可变结缔组织的一个典型例子，它可以快速可逆地改变其机械特性。这种反应的确切机制尚不清楚，但通常认为与胶原纤维之间的基质有关。CA含有肌纤维，但它们对CA的机械性能的贡献被认为是微不足道的，因为它们很少。然而，最近提出了一个模型，假设这些肌肉纤维在CA的行为中发挥重要作用。该模型的有效性是有争议的，我们认为有必要重新研究CA的生理学，将我们的注意力集中在肌肉纤维的作用上。我们发现，2，3-丁二酮单肟（BDM），一种已知的肌球蛋白跨桥抑制剂，可逆地抑制“捕捉”和放松的僵硬CA的Anthocidaris crassispina在浓度，阻止脊柱肌肉的收缩。在初步实验中，BDM对已知不含肌纤维的迪亚德马setosum脊柱中央韧带的机械性能没有影响。我们的研究结果表明，在CA的Anthocidaris的“捕获”取决于肌纤维中的肌球蛋白的活性。我们讨论了一个模型的捕获机制在CA。

The catch apparatus (CA) is a collagenous ligament that surrounds the joint at the base of each spine of the sea urchin. A classic example of mutable connective tissue, it can change its mechanical properties quickly and reversibly. The precise mechanism of the response is unknown, but it is generally thought to involve the ground substances between the collagen fibrils. The CA contains muscle fibres but their contribution to the mechanical properties of the CA has been thought insignificant because they were so few. Nevertheless, a model has recently been proposed that assumes a major role for these muscle fibres in the behavior of the CA.The validity of the model is controversial, and we thought it was necessary to re-investigate the physiology of the CA, focusing our attention on the role of the muscle fibres. We found that 2,3-butanedione monoxime (BDM), a known inhibitor of myosin crossbridges, reversibly inhibits 'catch' and relaxes a stiffened CA of Anthocidaris crassispina at concentrations that block contraction of the spine muscle. In preliminary experiments, BDM had no effect on the mechanical properties of the central ligament of the spine of Diadema setosum which has been known to contain no muscle fibres. Our results indicate that the 'catch' in the CA of Anthocidaris depends on the activity of myosin in the muscle fibres. We discuss a model for the catch mechanism in the CA.