Intracellular elasticity and viscosity in the body, leading, and trailing regions of locomoting neutrophils

Intracellular elasticity and viscosity in the body, leading, and trailing r egions of locomoting neutrophils. Am. J. Physiol. 277 (Cell Physiol. 46): C 432-C440, 1999.-To investigate the mechanisms underlying pseudopod protrusi on in locomoting neutrophils, we measured the intracellular stiffness and v iscosity in the leading region, main body, and trailing region from displac ements of oscillating intracellular granules driven with an optical trap. E xperiments were done in control conditions and after treatment with cytocha lasin D or nocodazole. We found 1) in the body and trailing region, the gra nules divided into a "fixed" population (too stiff to measure) and a "free" population (easily oscillated; fixed fraction 65%, free fraction 35%). By contrast, the fixed fraction in the leading region was <5%. 2) In the body and trailing region, there was no difference in stiffness or viscosity, but both were sharply lower in the leading region (respectively, 20-fold and 5 -fold). 3) Neither cytochalasin D nor nocodazole caused a decrease in stiff ness, but both treatments markedly reduced the fixed fraction in the body a nd trailing region to <20% and <40%, respectively. These observations sugge st a discrete lattice structure in the body and trailing region and suggest that the developing pseudopod has a core that is more fluidlike, in the se nse of a much lower viscosity and an almost total loss of stiffness. This i s consistent with the contraction/solation hypothesis of pseudopodial forma tion.