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

Abstract

To investigate the mechanisms underlying pseudopod protrusion in locomoting neutrophils, we measured the intracellular stiffness and viscosity in the leading region, main body, and trailing region from displacements of oscillating intracellular granules driven with an optical trap. Experiments were done in control conditions and after treatment with cytochalasin D or nocodazole. We found 1) in the body and trailing region, the granules 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 stiffness, but both treatments markedly reduced the fixed fraction in the body and trailing region to <20% and <40%, respectively. These observations suggest 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 sense of a much lower viscosity and an almost total loss of stiffness. This is consistent with the contraction/solation hypothesis of pseudopodial formation.

Human neutrophil surface protrusion under a point load: location independence and viscoelasticity

“…Coincidentally, the protrusional stiffness of passive neutrophils measured here is very close in magnitude to the intracellular uniaxial stiffness of crawling neutrophils measured by Yanai et al (47). Furthermore, the characteristic relaxation time shown in Fig.…”

Vacuolar-type H+-ATPases at the plasma membrane regulate pH and cell migration in microvascular endothelial cells

“…The variation in the steady-state deprotonated-to-protonated SNARF-1 ratio may be due to actual pH cyt differences, variations in regional cytoplasmic microviscosity (28, 43,55,66), or even a different proportion of dye bound to cytoplasmic proteins (4). To properly interpret the differences in SNARF-1 protonated-to-deprotonated ratios, we have taken into account the behavior of the pH fluoroprobe in the cytoplasm, because it is heterogeneous in terms of composition and organization.…”

Mechanical properties of cultured human airway smooth muscle cells from 0.05 to 0.4 Hz

“…Although the oscillatory mechanics of reconstituted gels of the cytoskeletal filaments have been well studied (24,32,36), there have been relatively few investigations of the oscillatory mechanics of the intact living cell. In studies of the oscillatory mechanics, the cell was probed with the use of a variety of techniques: through the cell surface by atomic force microscopy (46), from the interior by oscillating intracellular granuoles using laser tracking (60), along the cell longitudinal axis using glass manipulators (47), or in a cell pellet using oscillating disk rheometry (12,23). However, no study has yet reported the oscillatory mechanics of the cell by accessing the cytoskeleton through direct attachments to focal adhesions.…”