Tension modulates cell surface motility: A scanning acoustic microscopy study

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Abstract
The subtraction of subsequent scanning acoustic microscope images (SubSAM) of living cells taken in distinct time intervals reveals subcellular motility domains that are dependent on metabolic energy and correspond to cell surface deformations like protrusions, ruffling, and microblebs. This motility can be quantitated by determining the changes of the grey levels vs. time. Tension has been postulated as a global parameter in the control of cell shape and cell surface motility [Albrecht‐Bühler 1987: Cell Motil. Cytoskeleton 7:54–67; Bereiter‐Hahn et al., 1995: Biochem. Cell Biol. 73:337–348; Sheetz and Dai, 1996: Trends Cell Biol. 6:85–89]. For direct evaluation, the activity of the motility domains was measured while applying external tension (stretching) or internal tension (contraction induced by nocodazole) and by relaxation due to desintegration of the actin‐cytoskeleton using low concentrations of cytochalasin D (0.5 μg/ml). Elevated tension, regardless of how it is generated, externally or internally, whether directed or isotropic, lowers cell surface motility. In contrast, the relaxation of the cell cortex by cytochalasin D increases cell surface motility. Thus, a direct relationship between tension at the cell surface and surface motility was established as has been suggested by Sheetz and Dai [1996: Trends Cell Biol. 6:85–89] Cell Motil Cytoskeleton 43:349–359, 1999.