Valberg P A, Albertini D F
J Cell Biol. 1985 Jul;101(1):130-40. doi: 10.1083/jcb.101.1.130.
The motions of magnetic particles contained within organelles of living cells were followed by measuring magnetic fields generated by the particles. The alignment of particles was sensed magnetometrically and was manipulated by external fields, allowing non-invasive detection of particle motion as well as examination of cytoplasmic viscoelasticity. Motility and rheology data are presented for pulmonary macrophages isolated from lungs of hamsters 1 d after the animals had breathed airborne gamma-Fe2O3 particles. The magnetic directions of particles within phagosomes and secondary lysosomes were aligned, and the weak magnetic field produced by the particles was recorded. For dead cells, this remanent field was constant, but for viable macrophages, the remanent field decreased rapidly so that only 42% of its initial magnitude remained 5 min after alignment. A twisting field was applied perpendicular to the direction of alignment and the rate at which particles reoriented to this new direction was followed. The same twisting was repeated for particles suspended in a series of viscosity standards. Based on this approach, the low-shear apparent intracellular viscosity was estimated to be 1.2-2.7 X 10(3) Pa.s (1.2-2.7 X 10(4) poise). Time-lapse video microscopy confirmed the alignment of ingested particles upon magnetization and showed persistent cellular motility during randomization of alignment. Cytochalasin D and low temperature both reduced cytoplasmic activity and remanent-field decay, but affected rheology differently. Magnetic particles were observed in association with the microtubule organizing center by immunofluorescence microscopy; magnetization did not affect microtubule distribution. However, both vimentin intermediate filaments and f-actin reorganized after magnetization. These data demonstrate that magnetometry of isolated phagocytic cells can probe organelle movements, rheology, and physical properties of the cytoskeleton in living cells.
通过测量活细胞细胞器内磁性颗粒产生的磁场，追踪其运动。颗粒的排列通过磁力测定法进行检测，并由外部磁场进行操控，从而实现对颗粒运动的非侵入性检测以及对细胞质粘弹性的检测。本文给出了从吸入空气传播的γ-Fe₂O₃颗粒1天后的仓鼠肺中分离出的肺巨噬细胞的运动性和流变学数据。吞噬体和次级溶酶体内颗粒的磁方向是对齐的，并记录了颗粒产生的弱磁场。对于死细胞，这种剩余磁场是恒定的，但对于活的巨噬细胞，剩余磁场迅速下降，以至于在排列后5分钟仅保留其初始大小的42%。施加一个垂直于排列方向的扭转场，并追踪颗粒重新定向到这个新方向的速率。对悬浮在一系列粘度标准液中的颗粒重复相同的扭转操作。基于这种方法，低剪切表观细胞内粘度估计为1.2 - 2.7×10³Pa·s（1.2 - 2.7×10⁴泊）。延时视频显微镜证实了摄入颗粒在磁化时的排列，并显示在排列随机化过程中细胞持续运动。细胞松弛素D和低温都降低了细胞质活性和剩余场衰减，但对流变学的影响不同。通过免疫荧光显微镜观察到磁性颗粒与微管组织中心相关联；磁化不影响微管分布。然而，波形蛋白中间丝和f-肌动蛋白在磁化后都发生了重组。这些数据表明，分离的吞噬细胞的磁力测定法可以探测活细胞中细胞器的运动、流变学和细胞骨架的物理性质。
