Novel rheology of the human airway smooth muscle cell

We have developed a method for determining the mechanical impedance of the cytoskeleton (CSK) based on magnetic twisting cytometry. Ligand coated ferromagnetic beads were bound to the integrin receptors of human airway smooth muscle cells, and oscillatory torques applied with a magnetic field. Bead rotation was determined by measuring the oscillating magnetic field produced by the beads. The time course of stiffening in response to pharmacological agonists was also measured with a resolution of 10s. Apparent elastance (E) and viscosity (R) of the CSK were calculated from the complex ratio of specific magnetic torque to bead rotation. E increased weakly with oscillation frequency while R decreased inversely with frequency. Although the magnitudes of E and R were altered during changes in muscle activation, the frequency dependence was unchanged. This frequency dependence is known as structural damping, and is a novel finding for the mechanics of the CSK