Transport Imaging of Living Cells

Abstract

Living cells are out of equilibrium biological systems in which active and passive transports are literally of vital importance. Intracellular motion of a few types of particles has been studied before, but how these motions fit into the broader context of all physiological transports of the cell is still unclear. We used an unselective method - phase contrast imaging - to detect virtually all intracellular movements. Fourier analysis of movies of living HEP2 cells shows that cellular motions lack a well defined characteristic time. Movements observed in the 0.5 s to 655 s range were very information rich, showing self-similar temporal behavior in all locations inside the cell. To grab this information, a transport image of the living cell was constructed by representing the locally observed Hurst coefficient of the motions as a stand alone image. The cytoplasm of the cells was found to be dominated by superdiffusion driven by active transport. Brownian diffusion and subdiffusion was also observed, mostly inside the nucleus. We believe that the abundance of subdiffusion reports in the literature arises from the fact that the observed test particles or molecules were not integral part of the intracellular physiology. We propose the use of unselective microscopy methods and Hurst coefficient transport imaging as an effective tool to visualize physiological transport processes of living cells.