Changes in the mechanical properties of fibroblasts during spreading: a micromanipulation study.
European Biophysics Journal. 1999-03-09; 28(3): 222-234
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1. Eur Biophys J. 1999;28(3):222-34.
Changes in the mechanical properties of fibroblasts during spreading: a
Thoumine O(1), Cardoso O, Meister JJ.
(1)Biomedical Engineering Laboratory, Swiss Federal Institute of Technology,
Cell morphology is controlled in part by physical forces. If the main mechanical
properties of cells have been identified and quantitated, the question remains of
how the cell structure specifically contributes to these properties. In this
context, we addressed the issue of whether cell rheology was altered during cell
spreading, taken as a fundamental morphological change. On the experimental side,
we used a novel dual micromanipulation system. Individual chick fibroblasts were
allowed to spread for varying amounts of time on glass microplates, then their
free extremity was aspirated into a micropipet at given pressure levels. Control
experiments were also done on suspended cells. On the theoretical side, the cell
was modeled as a fluid drop of viscosity mu, bounded by a contractile cortex
whose tension above a resting value was taken to be linearly dependent on surface
area expansion. The pipet negative pressure was first adjusted to an equilibrium
value, corresponding to formation of a static hemispherical cap into the pipet.
This allowed computation, through Laplace’s law, of the resting tension (tau 0),
on the order of 3 x 10(-4) N/m. No difference in tau 0 was found between the
different groups of cells studied (suspended, adherent for 5 min, spread for 0.5
h, and spread for 3 h). However, tau 0 was significantly decreased upon treatment
of fibroblasts with inhibitors of actin polymerization or myosin function. Then,
the pressure was set at 30 mmH2O above the equilibrium pressure. All cells showed
a biphasic behavior: (1) a rapid initial entrance corresponding to an increase in
surface area, which was used to extract an area expansion elastic modulus (K), in
the range of 10(-2) N/m; this coefficient was found to increase up to 40% with
cell spreading; (2) a more progressive penetration into the pipet, linear with
time; this phase, attributed to viscous behavior of the cytoplasm, was used to
compute the apparent viscosity (mu, in the range of 2-5 x 10(4) Pa s) which was
found to increase by as much as twofold with cell spreading. In some experiments
the basal force at the cell-microplate interface was quantitated with flexible
microplates and found to be around 1 nN, in agreement with values calculated from
the model. Taken together, our results indicate a stiffening of fibroblasts upon
spreading, possibly correlated with structural organization of the cytoskeleton
during this process. This study may help understand better the morphology of
fibroblasts and their mechanical role in connective tissue integrity.
PMID: 10192936 [Indexed for MEDLINE]