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1 Unitat de Biofisica i Bioenginyeria, Facultat de Medicina, Universitat de Barcelona-IDIBAPS, Barcelona, Barcelona, Spain
* To whom correspondence should be addressed. E-mail: dnavajas{at}ub.edu.
The mechanical properties of alveolar epithelial cells play a central role in maintaining the physical integrity of the alveolar epithelium. We studied the viscoelastic properties of alveolar epithelial cells (A549) in response to thrombin and histamine with optical magnetic twisting cytometry. Ferrimagnetic beads coated with RGD-peptide or acLDL were bound to cell surface receptors and subsequently twisted in an oscillatory magnetic field (0.1 Hz - 100 Hz). The cell storage (G') and loss (G") moduli were computed from twisting torque and bead displacement. In measurements with RGD-coated beads, thrombin (0.5 U/ml) induced a rapid and sustained 3-fold increase in G' and G" at ~100 s after challenge. Histamine (100 µM) induced a rapid but transient 2-fold increase in G' and G" with maximum values 60 s after challenge. Post-treatment with cytochalasin D abolished thrombin-induced cell stiffening. G' increased with frequency following a power law with exponent 0.214. G" increased proportionally to G' up to 10 Hz but showed a steeper rise at higher frequencies. Thrombin caused a fall in the power law exponent (0.164). In measurements with acLDL-coated beads, minor changes (<20%) were observed in G' and G" after the addition of thrombin and histamine. F-actin staining revealed that thrombin and histamine induced a profound reorganization of the actin cytoskeleton at the cell periphery and formation of actin bundles. In the mechanically dynamic environment of the lung, cell stiffening induced by thrombin and histamine increases centripetal tension, which could contribute to alveolar barrier dysfunction.
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