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First published online 8 January 2003
doi: 10.1242/jcs.00230

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Local force induced conical protrusions of phagocytic cells

Laurent Vonna^1,*, Agnès Wiedemann², Martin Aepfelbacher² and Erich Sackmann^1,

¹ Physik Depatment E22 (biophysics group), Technische Universität München, D-85748 Garching, Germany
² Max von Pettenkofer Institut für Medizinische Mikrobiologie, Pettenkoferstrasse 9, Ludwig Maximilian Universität, D-80336 München, Germany
Present address: Institute of Theoretical Physics, UCSB, Santa Barbara, USA

View larger version (50K): [in a new window]   Fig. 1. Time evolution of formation of protrusion of macrophage induced by application of an external force pulse with an amplitude of 2 nN and 90 seconds duration. The phase contrast images (A,B) correspond to the beginning and the end of the pulse. The position of the magnetic tweezers in the direction of the force is plotted as a function of time. The inset shows the initial state of the deformation at higher time resolution to expose the initial elastic response more clearly.

View larger version (16K): [in a new window]   Fig. 2. Measurement of average velocity of beads pulled by the external force as a function of force amplitude. The enforced formation of protrusions was repeated several times for each cell. Examples are given for three different cells. On each image we have indicated the sequence number of the applied pulses in the whole series to demonstrate that the force does not depend on the prehistory of the sequence of the force application.

View larger version (37K): [in a new window]   Fig. 3. Time evolution of deflection of the bead after stepwise reduction of the force amplitude from f0=2.55 nN to 1.70 nN at position (a), to 0.85 nN at position (b) and to 0 nN at position (c). The arrows indicate the initial elastic relaxation after the reduction of the pulse. The double arrows at the end of the force pulse indicate the elastic regime of retraction.

View larger version (41K): [in a new window]   Fig. 4. Demonstration of active retraction of a protrusion against an external force of 3.55 nN.

View larger version (58K): [in a new window]   Fig. 5. Time evolution of protrusion of a macrophage after incubation with 10 µM Latrunculin A for 4 minutes. Phase contrast images at the beginning of the pulse (A), at the end of the viscoelastic response (B), at the end of the force pulse (C) and after relaxation (D) are shown. Note that the flow velocity in the viscoelastic regime (v1.6 µm second-1) is much higher then in the case of control cells.

View larger version (65K): [in a new window]   Fig. 6. Contour of trumpet-like protrusion of a cell enforced by nearly point-like force applied to the tip of the protrusion. R is the radius of the disk and a the radius of the bead.