Reappraisal of the connective-tissue catch hypothesis in echinoderms.

捕获器(CA)是一种胶原性韧带，环绕着海胆每根脊骨的关节。作为可变结缔组织的经典例子，它可以快速且可逆地改变其机械性能。这种反应的确切机制尚不清楚，但通常认为它涉及胶原纤维之间的基质物质。CA含有肌肉纤维，但它们对CA的力学性能的贡献一直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，该模型假定这些肌肉纤维在CA的行为中起主要作用。该模型的有效性存在争议，我们认为有必要重新研究CA的生理学，将注意力集中在肌肉纤维的作用上。我们发现，已知的肌球蛋白交叉桥的抑制剂2，3-丁二酮单肟(BDM)，在阻止脊椎肌肉收缩的浓度下，可逆地抑制‘Catch’并松弛粗刺花色藻僵硬的CA。在初步实验中，BDM对已知不含肌肉纤维的刚毛双毛虫脊椎中央韧带的机械性能没有影响。我们的结果表明，花色蛾CA中的“捕获物”取决于肌纤维中肌球蛋白的活性。我们讨论了CA中捕获机制的一个模型。

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.