Abstract
We have investigated changes in cellular deformability during promyelocytic leukemic HL-60 cell maturation. HL-60 cells were induced to mature with 1.25% dimethyl sulfoxide. Cellular deformability was evaluated by single-cell micropipette aspiration at one day, four days and seven days after induction. HL-60 cells were found to decrease in size and increase in deformability with maturation. When tested under the same aspiration pressures (0.5–1.3 kPa), cytoplasmic viscosity was found to vary from 210 to 85 Pa·s for cells prior to induction; it varied from 85 to 40 Pa·s for cells seven days after induction. Further, cytoplasmic viscosity exhibits power-law dependence on shear rate, μ = μ c (γ m/γ c) −b, where μ is cytoplasmic viscosity, γ m is mean shear rate during cell entry, μ c is the characteristic viscosity at the characteristic shear rate, γ c, and b is a material coefficient. Cells of all maturities showed similar dependence on shear rate (b0.5), but the characteristic viscosity decreased with maturation except for Day 1. When γ c was set to 1 s −1, μ c = 236 ± 5 Pa·s for cells prior to induction, μ c= 239 ± 7, 209 ± 7 and 175 ± 14 Pa·s for cells on Days 1, 4 and 7 of induction, respectively.
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