Measurement of local viscoelasticity and forces in living cells by magnetic tweezers
Measurement of local viscoelasticity and forces in living cells by magnetic tweezers
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DOI：
10.1016/s0006-3495(99)77225-5
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发表时间：
1999-01-01
影响因子：
3.4
通讯作者：
Sackmann, E
中科院分区：
文献类型：
--
作者：
Bausch, AR;Möller, W;Sackmann, E
我们用新近研制的显微流变仪测量了J774巨噬细胞胞质的粘弹性。铁磁珠（直径1.3 μ m）用于确定局部粘弹性模量。将步进力脉冲施加到磁珠上，并通过单粒子跟踪观察位移。通过分析蠕变响应曲线的三相力学等效电路，我们测量的剪切弹性模量，有效粘度，和应变松弛时间。剪切模量的值在细胞群内变化超过一个数量级（范围，20-735 Pa;平均值，343 Pa），并且在单个细胞内变化2倍。细胞质的有效粘度表现出相对尖锐的分布，平均约为eta = 210 Pa s（+/-143 Pa s）。我们通过观察微珠的诱导运动来测量由局部力产生的位移场。即使在1 μ m的顺序的距离，没有诱导的运动被认为是，这表明细胞质是由密集的和交联的细丝分开的软区域的集群。在另一系列实验中，我们分析了在恒定磁力下铁磁珠的磁泳运动。测量平行于和垂直于所施加的力的珠速度显示珠上的局部主动力在50至900 pN之间变化。
We measured the viscoelastic properties of the cytoplasm of J774 macrophages with a recently developed microrheometer. Ferromagnetic beads (1.3 mu m in diameter) were used to determine the local viscoelastic moduli. Step-force pulses were applied to the magnetic beads and the displacement was observed by single particle tracking. By analyzing the creep response curves in terms of a triphasic mechanical equivalent circuit, we measured the shear elastic modulus, the effective viscosities, and the strain relaxation time. The values of the shear modulus vary by more than an order of magnitude within the cell population (range, 20-735 Pa; average, 343 Pa) and by a factor of 2 within single cells. The effective viscosity of the cytoplasm exhibits a relatively sharp distribution about an average of eta = 210 Pa s (+/- 143 Pa s). We measured the displacement field generated by the local forces by observing the induced motion of nonmagnetic beads. Even at distances of the order of 1 mu m, no induced motion was seen, suggesting that the cytoplasm is composed of clusters of densely packed and cross-linked filaments separated by soft regions. In another series of experiments we analyzed the magnetophoretic motion of the ferromagnetic beads at a constant magnetic force. Measuring the bead Velocity parallel and perpendicular to the applied force showed that local active forces on the beads varied from 50 to 900 pN.