Measuring Local Viscosities near Plasma Membranes of Living Cells with Photonic Force Microscopy.
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.
Laboratory for Bio- and Nano-Photonics, Department of Microsystems Engineering, University of Freiburg, Germany.
Felix
F
Jünger
Laboratory for Bio- and Nano-Photonics, Department of Microsystems Engineering, University of Freiburg, Germany.
Felix
F
Kohler
Laboratory for Bio- and Nano-Photonics, Department of Microsystems Engineering, University of Freiburg, Germany.
Andreas
A
Meinel
Macromolecular Modelling Group, Institute of Chemistry and Biochemistry, Freie Universität Berlin, Berlin, Germany.
Tim
T
Meyer
Life Imaging Center (LIC) and Center for Biological Systems Analysis (ZBSA), University of Freiburg, Freiburg, Germany.
Roland
R
Nitschke
Laboratory for Bio- and Nano-Photonics, Department of Microsystems Engineering, University of Freiburg, Germany.
Birgit
B
Erhard
Laboratory for Bio- and Nano-Photonics, Department of Microsystems Engineering, University of Freiburg, Germany; BIOSS Centre for Biological Signalling Studies, University of Freiburg, Freiburg, Germany. Electronic address: rohrbach@imtek.de.
Alexander
A
Rohrbach
D000818:Animals; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism*; D002470:Cell Survival; D004285:Dogs; D006801:Humans; D057446:Hydrodynamics; D021621:Imaging, Three-Dimensional; D007368:Interferometry; D051379:Mice; D008853:Microscopy; D052898:Optical Tweezers; D017785:Photons; D011554:Pseudopodia / Q000378:metabolism; D053835:Unilamellar Liposomes / Q000378:metabolism; D014783:Viscosity
D053835:Unilamellar Liposomes