Mechanical properties of alveolar epithelial cells in culture

With the use of magnetic twisting cytometry, we characterized the mechanica l properties of rat type II alveolar epithelial (ATII) cells in primary cul ture and examined whether the cells' state of differentiation and the appli cation of deforming stresses influence their resistance to shape change. Ce lls were harvested from rat lungs as previously described (Dobbs LG. Am J P hysiol Lung Cell Mol Physiol 258: L134-L147, 1990) and plated at a density of 1 x 10(6) cells/cm(2) in fibronectin-coated 96 Remova wells, and their m echanical properties were measured 2-9 days later. We show 1) that ATII cel ls form much stronger bonds with RGD-coated beads than they do with albumin - or acetylated low-density lipoprotein-coated beads, 2) that RGD-mediated bonds seemingly "mature" during the first 60 min of bead contact, 3) that t he apparent stiffness of ATII cells increases with days in culture, 4) that stiffness falls when the RGD-coated beads are intermittently oscillated at 0.3 Hz, and 5) that this fall cannot be attributed to exocytosis-related r emodeling of the subcortical cytoskeleton. Although the mechanisms of force transfer between basement membrane, cytoskeleton, and plasma membrane of A TII cells remain to be resolved, such analyses undoubtedly require definiti on of the cell's mechanical properties. To our knowledge, the results prese nted here provide the first data on this topic.