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

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Abstract
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 (G′) and loss modulus (G") from the applied torque and the resulting rotational motion of the beads as determined from their remanent magnetic field. Under baseline conditions, G′ increased weakly with frequency, whereas G" was independent of the frequency. The cell was predominantly elastic, with the ratio of G" to G′ (defined as η) being ∼0.35 at all frequencies. G′ and G" increased together after contractile activation and decreased together after deactivation, whereas η remained unaltered in each case. Thus elastic and dissipative stresses were coupled during changes in contractile activation. G′ and G" decreased with disruption of the actin fibers by cytochalasin D, but η 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.