|Budget Amount *help
¥2,900,000 (Direct Cost : ¥2,900,000)
Fiscal Year 1999 : ¥1,300,000 (Direct Cost : ¥1,300,000)
Fiscal Year 1998 : ¥1,600,000 (Direct Cost : ¥1,600,000)
To investigate the mechanisms underlying pseudopod protrusion in locomoting neutrophils, we measured the intracellular stiffness and viscosity in the leading region (L), main body (B), and trailing region (T) from displacements of oscillating intracellular granules driven with an optical trap. Experiments were done in control conditions, and following treatment with cytochalasin D or nocodazole. We found (1) in B and T, 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 L was <5%. (2) In B and T, there was no difference in stiffness or viscosity, but both were sharply lower in L (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 B and T to <20% and <40% respectively. These observations suggest a discrete lattice structure in B and T, and that the developing pseudopod has a core that is more fluid-like, 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.