The Journal of Cell Biology, Vol 109, 2233-2243, Copyright © 1989 by The Rockefeller University Press

ARTICLES

Viscoelasticity of F-actin measured with magnetic microparticles

KS Zaner and PA Valberg
Hematology-Oncology Section, Boston City Hospital, Massachusetts.

Dispersed submicroscopic magnetic particles were used to probe viscoelasticity for cytoplasm and purified components of cytoplasm. An externally applied magnetic field exerted force on particles in cells, in filamentous actin (F-actin) solutions, or in F-actin gels formed by the addition of the actin gelation factor, actin-binding protein (ABP). The particle response to magnetic torque can be related to the viscoelastic properties of the fluids. We compared data obtained on F- actin by the magnetic particle method with data obtained on F-actin by means of a sliding plane viscoelastometer. F-actin solutions had a significant elasticity, which increased by 20-fold when gels were formed by ABP addition. Both methods gave consistent results, but the dispersed magnetic particles indicated quantitatively greater rigidity than the viscoelastometer (two and six times greater for F-actin solutions and for F-actin plus ABP gels, respectively). These differences may be due to the fact that, compared with traditional microrheometers, dispersed particle measurements are less affected by long-range heterogeneity or domain-like structure. The magnetometric method was used to examine the mechanical properties of cytoplasm within intact macrophages; the application of the same magnetometric technique to both cells and well-defined, purified protein systems is a first step toward interpreting the results obtained for living cells in molecular terms. The magnetic particle probe system is an effective nonoptical technique for determining the motile and mechanical properties of cells in vitro and in vivo.
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This article has been cited by other articles:

• Beysens, D. A., Forgacs, G., Glazier, J. A. (2000). Cell sorting is analogous to phase ordering in fluids. Proc. Natl. Acad. Sci. USA 97: 9467-9471 [Abstract] [Full Text]  
• Wang, N, Butler, J., Ingber, D. (1993). Mechanotransduction across the cell surface and through the cytoskeleton. Science 260: 1124-1127 [Abstract]  

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