Dynamic study of cell mechanical and structural responses to rapid changesof calcium level

Cell shape control is complex since it may involve multiple cytoskeletal co mponents and metabolic pathways. Here we present a kinetic study of the mec hanical and structural responses of cells from the monocytic THP-1 line to a rapid increase of cytosolic calcium level. Cells were exposed to ionomyci n in a medium of varying calcium concentration and they were probed at regu lar intervals for (1) cortical rigidity as determined with micropipette asp iration, and (2) content and distribution of polymerized actin, myosin or A BP-280, as determined with flow cytometry and/or confocal microscopy. An in crease of free intracellular calcium level induced: (1) a biphasic deformab ility change with marked stiffening within a second, and significant soften ing a minute later; (2) a biphasic change of actin polymerization with init ial decrease (within less than a second) and rapid recovery (within a few s econds); (3) a topographical redistribution of microfilaments with an oscil latory behavior of the cortical fraction, while no substantial redistributi on of myosin or ABP-280 was detected. It is suggested that a regulation of cell rigidity might be achieved without any structural change by suitable m odulation of the lifetime of bridges formed between microfilaments by actin binding proteins. Cell Motil. (C) 2000 Wiley-Liss, Inc.