Huang B, Pitelka D R
J Cell Biol. 1973 Jun;57(3):704-28. doi: 10.1083/jcb.57.3.704.
The structural basis for the function of microtubules and filaments in cell body contractility in the ciliate Stentor coeruleus was investigated. Cells in the extended state were obtained for ultrastructural analysis by treatment before fixation with a solution containing 10 mM EGTA, 50-80 mM Tris, 3 mM MgSO(4), 7.5 mM NH(4)Cl, 10 mM phosphate buffer (pH 7.1). The response of Stentor to changes in the divalent cation concentrations in this solution suggests that Ca(+2) and Mg(+2) are physiologically important in the regulation of ciliate contractility. The generation of motive force for changes in cell length in Stentor resides in two distinct longitudinal cortical fiber systems, the km fibers and myonemes. Cyclic changes in cell length are associated with (a) the relative sliding of parallel, overlapping microtubule ribbons in the km fibers, and (b) a distinct alteration in the structure of the contractile filaments constituting the myonemes. The microtubule and filament systems are distinguished functionally as antagonistic contractile elements. The development of motive force for cell extension is accomplished by active microtubule-to-microtubule sliding generated by specific intertubule bridges. Evidence is presented which suggests that active shortening of contractile filaments, reflected in a reversible structural transformation of dense 4-nm filaments to tubular 10-12-nm filaments, provides the basis for rapid cell contraction.
对纤毛虫蓝喇叭虫（Stentor coeruleus）细胞体收缩性中微管和细丝功能的结构基础进行了研究。通过在固定前用含有10 mM乙二醇双四乙酸（EGTA）、50 - 80 mM Tris、3 mM硫酸镁（MgSO₄）、7.5 mM氯化铵（NH₄Cl）、10 mM磷酸盐缓冲液（pH 7.1）的溶液处理，获得处于伸展状态的细胞用于超微结构分析。喇叭虫对该溶液中二价阳离子浓度变化的反应表明，钙离子（Ca²⁺）和镁离子（Mg²⁺）在纤毛虫收缩性调节中具有重要生理意义。喇叭虫细胞长度变化的驱动力产生于两个不同的纵向皮质纤维系统，即km纤维和肌原纤维。细胞长度的周期性变化与（a）km纤维中平行、重叠的微管带的相对滑动，以及（b）构成肌原纤维的收缩细丝结构的明显改变有关。微管和细丝系统在功能上被区分为拮抗收缩元件。细胞伸展驱动力的产生是通过特定微管间桥产生的微管与微管之间的主动滑动来实现的。有证据表明，收缩细丝的主动缩短反映在致密的4纳米细丝向管状的10 - 12纳米细丝的可逆结构转变中，为细胞快速收缩提供了基础。
