Berlin 2008 – wissenschaftliches Programm
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BP: Fachverband Biologische Physik
BP 7: Posters I
BP 7.16: Poster
Montag, 25. Februar 2008, 17:00–19:30, Poster A
Optical force based investigations of cell mechanical concepts during phagocytosis — •Felix Kohler1, Holger Kress2, and Alexander Rohrbach1 — 1University Freiburg, Freiburg, Germany — 2Yale University, New Haven, USA
Macrophages internalize bacteria during phagocytosis, which is a central mechanism in the immune system. Still, only little is known about the mechanical properties of phagocytosis, in particular when mediated by cellular tentacles, i.e. filopodia. We used optical tweezers-based microscopy to investigate different mechanical concepts of the cell to take up 1 micron beads, which serve as synthetic bacteria. The motion of an optically trapped bead was tracked interferometrically in 3D with nanometer precision at a microsecond timescale. On the one hand, the measurement of the thermal bead fluctuations during the binding to the cell membrane enabled the observation of individual receptor-ligand bond formation. On the other hand, the measurement of the mean bead displacements allowed determining retraction forces of filopodia at various retraction speeds. We measured F-actin dependent 36-nanometer steps inside living cells during filopodia retraction likely belonging to actin-based molecular motors[1]. Steps remained clearly visible even at force regimes clearly beyond the stall force of a single myosin motor. This seems to indicate a kind of inter-motor coupling, a phenomenon which we try to explain by a stochastic multi-state model.
[1] Kress, H., E.H.K. Stelzer, D. Holzer, F. Buss, G. Griffiths, and A. Rohrbach, PNAS, Vol.104, 2007, 11633 - 11638