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

Abstract

. Mechanical properties of cultured human airway smooth muscle cells from 0.05 to 0.4 Hz. J Appl Physiol 89: 1619-1632, 2000.-We investigated the rheological properties of living human airway smooth muscle cells in culture and monitored the changes in rheological properties induced by exogenous stimuli. We oscillated small magnetic microbeads bound specifically to integrin receptors and computed the storage modulus (GЈ) and loss modulus (GЉ) from the applied torque and the resulting rotational motion of the beads as determined from their remanent magnetic field. Under baseline conditions, GЈ increased weakly with frequency, whereas GЉ was independent of the frequency. The cell was predominantly elastic, with the ratio of GЉ to GЈ (defined as ) being ϳ0.35 at all frequencies. GЈ and GЉ increased together after contractile activation and decreased together after deactivation, whereas remained unaltered in each case. Thus elastic and dissipative stresses were coupled during changes in contractile activation. GЈ and GЉ decreased with disruption of the actin fibers by cytochalasin D, but increased. These results imply that the mechanisms for frictional energy loss and elastic energy storage in the living cell are coupled and reside within the cytoskeleton. cytoskeleton; storage modulus; viscoelasticity; contraction; structural damping; magnetic twisting cytometry PHYSICAL FORCES ACTING ON cells and the resulting cell deformations affect critical features of cell function, including proliferation, differentiation, wound healing, protein and DNA synthesis, apoptosis, cell shape, and cell motility (3,5,6,22). When deformed, a cell stores mechanical energy, and this stored energy permits subsequent recovery of shape. The cell also dissipates mechanical energy through mechanical friction. The structural origin for cell elasticity is widely believed to originate in the network of actin fibers within the cytoskeleton (50). However, the origin for energy dissipation is less clear but is often thought to arise from viscous mechanisms associated with shear of the cytoplasmic fluids (2,26,45,51).A common method to separate elastic from dissipative behavior for any material is to measure responses to oscillatory loads (21). 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. Focal adhesions are the mechanical connections linking the cytoskeleton of t...

Mechanical behavior in living cells consistent with the tensegrity model

“…Specifically, tensegrity predicts that at a given frequency, both the storage and loss moduli should increase with increasing prestress, whereas the hysteresivity coefficient (the fraction of the frictional energy loss relative to the elastic energy storage) should be independent of prestress. Importantly, this a priori prediction of the model is consistent with results of a recent experimental study in which the dynamic behavior of the same smooth muscle cells as used here were analyzed in response to a physiological range of frequencies (0.05 to 0.20 Hz) and forcing amplitude of Ϸ8 Pa, before and after addition of 10 M histamine (16). As predicted by the tensegrity model, both the storage and loss moduli increased (by roughly 70%), whereas the hysteresivity coefficient remained constant when contractility (prestress) was increased by histamine treatment.…”

“…4A) and the shear modulus (measured with oscillatory magnetic twisting cytometry; ref. 16; Fig. 4B) increased as the concentration of hista- mine, and thus the level of tension in the actin CSK, was raised.…”

“…Methods for coating microbeads (4.5 m diameter; Dynal, Great Neck, NY) with RGD-peptide (Peptite 2000; Integra, San Diego) and acetylated low-density lipoprotein (AcLDL; Biomedical Technology, Stoughton, MA) (12, 13), micromanipulation (13), immunofluorescence staining (14), cell culture (12)(13)(14)(15), and oscillatory magnetic twisting cytometry (16) have been published. A traction force microscopy technique (17) was adapted to create thin (50-70 m), flexible (Young's modulus Ϸ1,300 Pa; Poisson's ratio ϭ 0.48) sheets of polyacrylamide gel (2% acrylamide͞0.25% bis-acrylamide) containing 0.2 m fluorescent beads (FluoSpheres; Molecular Probes) and coated with type I collagen (0.2 mg͞ml; Collagen Biomedical Products, Bedford, MA).…”

Tensegrity-based mechanosensing from macro to micro

“…), we developed mathematical models of the cell based on tensegrity starting from first mechanistic principles that provide even more powerful a priori predictions relating to both cell static and dynamic mechanical behavior, which have now been confirmed experimentally in various cell types (Stamenovic et al, 1996;Coughlin and Stamenovic, 1998;Stamenovic and Coughlin, 1999;Stamenovic and Coughlin, 2000;Wang and Stamenovic, 2000;Stamenovic, 2005). Behaviors exhibited by living cells that can be predicted by the tensegrity model include: 1) linear relation between stiffness and applied stress (Wang et al, 1993;Wang and Ingber, 1994), 2) cell mechanics depends on prestress (Lee et al, 1998;Wang and Ingber, 1994), 3) linear relation between stiffness and prestress (Wang et al, 2001;Wang et al, 2002), 4) hysteresivity is independent of prestress (Maksym et al, 2000;Wang et al, 2001); 5) quantitative predictions of cellular elasticity (Stamenovic and Coughlin, 2000), 6) predictions of dynamic mechanical behavior (Sultan et al, 2004), and 7) mechanical contribution of intermediate filaments to cell mechanics.…”

Oscillatory magnetic tweezers based on ferromagnetic beads and simple coaxial coils

“…These beads can be subjected to a secondary magnetization in a weak magnetic field without rotation of magnetic domains, i.e., with no change in their magnetic moment. 23 This property of ferromagnetic ͑and ferrimagnetic͒ materials allowed the measurement of the mechanical properties of viscous solutions, 37 intracellular organelles, 38 and cytoskeleton 6,28,39 by twisting beads through a weak magnetic field in a direction different from that of the bead magnetic moment. Instead of applying a twisting torque, we used permanently magnetized beads to produce controlled translational forces.…”