Partitioning of cortical and deep cytoskeleton responses from transient magnetic bead twisting

We attempted to estimate in living adherent epithelial alveolar cells, the degree of structural and mechanical heterogeneity by considering two individualized cytoskeleton components, i.e., a submembranous cortical cytoskeleton and a deep cytoskeleton (CSK). F-actin structure characterizing each CSK component was visualized from spatial reconstructions at low and high density, respectively, especially in a 10-mum-cubic neighborhood including the bead. Specific mechanical properties (Young elastic and viscous modulus E and eta) were revealed after partitioning the magnetic twisting cytometry response using a double viscoelastic solid model with asymmetric plastic relaxation. Results show that the cortical CSK response is a faster (tau(1)less than or equal to0.7 s), softer (E-1: 63-109 Pa), moderately viscous (eta(1): 7-18 Pa s), slightly tensed, and easily damaged structure compared to the deep CSK structure which appears slower (tau(2)similar to 1/2 min), stiffer 2 (E-2: 95 - 204 Pa), highly viscous (eta(2): 760- 1967 Pa s), more tensed, and fully elastic, while exhibiting a larger stress hardening behavior. Adding drug depolymerizing actin filaments decreased predominantly the deep CSK stiffness. By contrast, an agent altering cell-matrix interactions affected essentially the cortical CSK stiffness. We concluded that partitioning the CSK within cortical and deep structures is largely consistent with their respective functional activities. (C) 2003 Biomedical Engineering Society.