Intracellular microrheology of motile Amoeba proteus.
The motility of Amoeba proteus was examined using the technique of passive particle tracking microrheology, with the aid of newly developed particle tracking software, a fast digital camera, and an optical microscope. We tracked large numbers of endogeneous particles in the amoebae, which displayed subdiffusive motion at short timescales, corresponding to thermal motion in a viscoelastic medium, and superdiffusive motion at long timescales due to the convection of the cytoplasm. Subdiffusive motion was characterized by a rheological scaling exponent of 3/4 in the cortex, indicative of the semiflexible dynamics of the actin fibers. We observed shear-thinning in the flowing endoplasm, where exponents increased with increasing flow rate; i.e., the endoplasm became more fluid-like. The rheology of the cortex is found to be isotropic, reflecting an isotropic actin gel. A clear difference was seen between cortical and endoplasmic layers in terms of both viscoelasticity and flow velocity, where the profile of the latter is close to a Poiseuille flow for a Newtonian fluid.
Rogers
Salman S
SS
Biological Physics Group, School of Physics and Astronomy, University of Manchester, Manchester M60 1QD, United Kingdom.
Waigh
Thomas A
TA
Lu
Jian R
JR
D000656:Amoeba / Q000502:physiology*; D000818:Animals; D002465:Cell Movement / Q000502:physiology*; D004548:Elasticity; D007424:Intracellular Fluid / Q000502:physiology*; D044085:Microfluidics / Q000379:methods*; D033081:Shear Strength; D014783:Viscosity