Jünger Felix, Kohler Felix, Meinel Andreas, Meyer Tim, Nitschke Roland, Erhard Birgit, Rohrbach Alexander
Laboratory for Bio- and Nano-Photonics, Department of Microsystems Engineering, University of Freiburg, Germany.
Macromolecular Modelling Group, Institute of Chemistry and Biochemistry, Freie Universität Berlin, Berlin, Germany.
Biophys J. 2015 Sep 1;109(5):869-82. doi: 10.1016/j.bpj.2015.07.027.
The molecular processes of particle binding and endocytosis are influenced by the locally changing mobility of the particle nearby the plasma membrane of a living cell. However, it is unclear how the particle's hydrodynamic drag and momentum vary locally and how they are mechanically transferred to the cell. We have measured the thermal fluctuations of a 1 μm-sized polystyrene sphere, which was placed in defined distances to plasma membranes of various cell types by using an optical trap and fast three-dimensional (3D) interferometric particle tracking. From the particle position fluctuations on a 30 μs timescale, we determined the distance-dependent change of the viscous drag in directions perpendicular and parallel to the cell membrane. Measurements on macrophages, adenocarcinoma cells, and epithelial cells revealed a significantly longer hydrodynamic coupling length of the particle to the membrane than those measured at giant unilamellar vesicles (GUVs) or a plane glass interface. In contrast to GUVs, there is also a strong increase in friction and in mean first passage time normal to the cell membrane. This hydrodynamic coupling transfers a different amount of momentum to the interior of living cells and might serve as an ultra-soft stimulus triggering further reactions.
颗粒结合和内吞作用的分子过程受活细胞质膜附近颗粒局部变化的迁移率影响。然而，尚不清楚颗粒的流体动力学阻力和动量如何局部变化，以及它们如何机械地传递到细胞。我们测量了一个1μm大小的聚苯乙烯球体的热涨落，该球体通过使用光镊和快速三维（3D）干涉粒子跟踪技术放置在与各种细胞类型的质膜有特定距离处。从30μs时间尺度上的粒子位置涨落，我们确定了在垂直和平行于细胞膜方向上粘性阻力随距离的变化。对巨噬细胞、腺癌细胞和上皮细胞的测量显示，与在巨型单层囊泡（GUVs）或平面玻璃界面处测量的结果相比，颗粒与膜的流体动力学耦合长度显著更长。与GUVs不同的是，垂直于细胞膜方向的摩擦力和平均首次通过时间也有显著增加。这种流体动力学耦合将不同量的动量传递到活细胞内部，并可能作为一种超软刺激触发进一步反应。
