Bausch A R, Möller W, Sackmann E
Physik Department E22 (Biophysics group), Technische Universität M unchen, D-85748 Garching,
Biophys J. 1999 Jan;76(1 Pt 1):573-9. doi: 10.1016/S0006-3495(99)77225-5.
We measured the viscoelastic properties of the cytoplasm of J774 macrophages with a recently developed microrheometer. Ferromagnetic beads (1.3 microm 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 microm, 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.
我们使用最近开发的微流变仪测量了J774巨噬细胞细胞质的粘弹性特性。使用铁磁珠（直径1.3微米）来确定局部粘弹性模量。向磁珠施加阶跃力脉冲，并通过单粒子跟踪观察位移。通过根据三相机械等效电路分析蠕变响应曲线，我们测量了剪切弹性模量、有效粘度和应变松弛时间。剪切模量的值在细胞群体中变化超过一个数量级（范围为20 - 735 Pa；平均值为343 Pa），在单个细胞内变化2倍。细胞质的有效粘度围绕平均值η = 210 Pa·s（±143 Pa·s）呈现出相对尖锐的分布。我们通过观察非磁性珠的诱导运动来测量局部力产生的位移场。即使在1微米左右的距离处，也未观察到诱导运动，这表明细胞质由被软区域隔开的密集堆积和交联细丝簇组成。在另一系列实验中，我们在恒定磁力下分析了铁磁珠的磁泳运动。测量平行和垂直于施加力的珠速度表明，作用在珠上的局部主动力在50到900 pN之间变化。
