Cohen I
Methods Achiev Exp Pathol. 1979;9:40-86.
The various manifestations of platelet activation are derived from a reorganization of components of the contractile and microtubular systems. The controversial initial stages of excitation-contraction coupling in platelets lead to the release of calcium from the dense tubular system, the morphological counterpart of the muscle sarcotubular closed vesicles. Calcium triggers the actin-myosin interaction and the developing force, possibly together with a local increase of the cation concentration, may cause the collapse of the microtubular ring and its reappearance in the forming long pseudopodia. Actin-myosin interaction is modulated by several factors among which tropomyosin-troponin, responsible for the calcium-sensitivity of contractile processes, and phosphorylation of one of the myosin light chains. Platelet actin is anchored to the membrane and its sliding towards the short myosin filaments may form the basis for platelet shape change. Platelet alpha-actinin and actin-binding protein are able to aggregate actin into an impressive gel. Therefore, the contractile proteins seem to have a double role in controlling the consistency of the cytoplasmic gel on the one hand, and the contractile manifestations related to motility on the other hand. One of the most important features of the 'contracted' platelet is the rigidity of the pseudopodia brought about by the 'gelification' of actin filaments and the presence of microtubules. A new model for clot contraction is proposed, based on the rigidity of the long spiky pseudopodia and on the motile properties of platelets. While migrating towards each other, the interlocking pseudopodia from different platelets adhere to the polymerizing fibrin, compressing the fibrin nets in their pathway. Since the anchoring of contractile fibers to membranes is crucial for the platelet contractile manifestations, the integrity of the membrane structure should be considered in the study of pathological aspects of platelet function.
血小板激活的各种表现源于收缩系统和微管系统成分的重新组织。血小板兴奋 - 收缩偶联存在争议的初始阶段会导致钙离子从致密管状系统释放，致密管状系统是肌肉肌管闭合囊泡在形态学上的对应物。钙离子触发肌动蛋白 - 肌球蛋白相互作用，产生的力量，可能与阳离子浓度的局部增加一起，可能导致微管环的塌陷以及其在形成的长伪足中重新出现。肌动蛋白 - 肌球蛋白相互作用受多种因素调节，其中原肌球蛋白 - 肌钙蛋白负责收缩过程的钙敏感性，以及肌球蛋白轻链之一的磷酸化。血小板肌动蛋白锚定在膜上，其向短肌球蛋白丝的滑动可能构成血小板形状改变的基础。血小板α - 辅肌动蛋白和肌动蛋白结合蛋白能够将肌动蛋白聚合成令人印象深刻的凝胶。因此，收缩蛋白似乎一方面在控制细胞质凝胶的稠度方面，另一方面在与运动性相关的收缩表现方面具有双重作用。“收缩”血小板最重要的特征之一是由肌动蛋白丝的“凝胶化”和微管的存在导致的伪足的刚性。基于长而尖的伪足的刚性和血小板的运动特性，提出了一种新的凝块收缩模型。在彼此靠近迁移时，来自不同血小板的相互交错的伪足附着在聚合的纤维蛋白上，压缩它们路径中的纤维蛋白网。由于收缩纤维与膜的锚定对于血小板收缩表现至关重要，在研究血小板功能的病理方面时应考虑膜结构的完整性。
