Berlin 2005 – scientific programme

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DY: Dynamik und Statistische Physik

DY 43: Einstein Symposium Brownian Motion, Diffusion and Beyond (SYBM) – Contributed Talks I

DY 43.4: Talk

Tuesday, March 8, 2005, 15:15–15:30, TU H2032

Intracellular Transport: A Levy Flight Process with a Log-Normal Velocity Distribution — •Erich Sackmann and Doris Heinrich — E22, Biophysik, Technische Universität München, Garching, Germany

The micro-viscoelastic behavior and intracellular transport in Dictyostelia cells has been evaluated by analysing the active and passive motion of magnetic and non-magnetic force probes, exploring a large region within the cell cytoplasm. A detailed analysis of the bead velocities showed that the motion can be described by Levy like quasi random walks, which can be represented by a log-normal distributions with velocities ranging from 0,25 -15 microns/s. The log-normal distribution is determined by the superposition of several distinct, statistically independent motions comprising the flagella like motion of the microtubules, the active motion of the bead along microtubules driven by kinesin and dynein motor molecules, the internal hydrodynamic flow, and the locomotion of the cell. The active forces measured in Dictyostelia cells (embedded in agarose) vary between 9 and 30 pN while larger forces (up to 100 pN) were found in free Dictyostelia. The large forces are attributed to actin-myosin mycromuscles. The cytoplasm behaves as a viscoplastic body. The force induced intracellular bead transport is described as a diffusive walk of a particle in a quasi-periodic potential and the mobility is determined by the fracture of intracellular networks. The direction is given by the constraints imposed by the microtubules and the intracellular compartment and the mobility has to be considered as a tensor.