Schliwa M, Euteneuer U, Bulinski J C, Izant J G
Proc Natl Acad Sci U S A. 1981 Feb;78(2):1037-41. doi: 10.1073/pnas.78.2.1037.
Detergent-extracted BSC-1 monkey cells have been used as a model system to study the Ca(2+) sensitivity of in vivo polymerized microtubules under in vitro conditions. The effects of various experimental treatments were observed by immunofluorescence microscopy. Whereas microtubules are completely stable at Ca(2+) concentrations below 1 muM, Ca(2+) at greater than 1-4 muM induces microtubule disassembly that begins in the cell periphery and proceeds towards the cell center. At concentrations of up to 500 muM, both the pattern and time course of disassembly are not markedly altered, suggesting that, within this concentration range, Ca(2+) effects are catalytic rather than stoichiometric. Higher (millimolar) Ca(2+) concentration results in rapid destruction of microtubules. Of other divalent cations, only Sr(2+) has a slight depolymerizing effect, whereas millimolar Ba(2+), Mg(2+), or Mn(2+) is ineffective. Disassembly induced by micromolar Ca(2+) is inhibited by pharmacological agents known to bind to calmodulin and inhibit its function, suggesting that calmodulin mediates Ca(2+) effects. Both the addition of exogenous brain microtubule-associated proteins (MAPs) after lysis and the retention of endogenous cellular MAPs normally extracted during the lysis step stabilize microtubules against the depolymerizing effect of micromolar Ca(2+). The results indicate that, in this model system, microtubules are sensitive to physiological Ca(2+) concentrations and that this sensitivity may be conferred by calmodulin associated with the microtubules. MAPs appear to have a modulating effect on microtubular Ca(2+) sensitivity and thus may function as a discriminating factor in cellular functions performed by calmodulin. It is hypothesized that Ca(2+)-stimulated microtubule disassembly depends on the relative amount of MAPs.
去污剂提取的BSC - 1猴细胞已被用作模型系统，以研究体外条件下体内聚合微管的Ca(2+)敏感性。通过免疫荧光显微镜观察各种实验处理的效果。当Ca(2+)浓度低于1μM时，微管完全稳定，而大于1 - 4μM的Ca(2+)会诱导微管解聚，解聚从细胞周边开始并向细胞中心进行。在高达500μM的浓度下，解聚的模式和时间进程没有明显改变，这表明在该浓度范围内，Ca(2+)的作用是催化性的而非化学计量性的。更高（毫摩尔）的Ca(2+)浓度会导致微管迅速破坏。在其他二价阳离子中，只有Sr(2+)有轻微的解聚作用，而毫摩尔浓度的Ba(2+)、Mg(2+)或Mn(2+)则无效。微摩尔Ca(2+)诱导的解聚被已知能结合钙调蛋白并抑制其功能的药物所抑制，这表明钙调蛋白介导了Ca(2+)的作用。裂解后添加外源脑微管相关蛋白（MAPs）以及保留通常在裂解步骤中提取的内源性细胞MAPs，都能使微管稳定，抵抗微摩尔Ca(2+)的解聚作用。结果表明，在这个模型系统中，微管对生理Ca(2+)浓度敏感，这种敏感性可能由与微管相关的钙调蛋白赋予。MAPs似乎对微管的Ca(2+)敏感性有调节作用，因此可能在钙调蛋白执行的细胞功能中作为一个区分因素发挥作用。据推测，Ca(2+)刺激的微管解聚取决于MAPs的相对含量。
