VISCOELASTIC RESPONSE OF FIBROBLASTS TO TENSION TRANSMITTED THROUGH ADHERENS JUNCTIONS

Cytoplasmic deformation was monitored by observing the displacements o f 200-nm green fluorescent beads microinjected into the cytoplasm of S wiss 3T3 fibroblasts. We noted a novel protrusion of nonruffling cell margins that was accompanied by axial flow of beads and cytoplasmic ve sicles as far as 50 mu m behind the protruding plasma membrane, Fluore scent analog cytochemistry and immunofluorescence localization of F-ac tin, alpha-actinin, N-cadherin, and beta-catenin showed that the protr uding margins of deforming cells were mechanically coupled to neighbor ing cells by adherens junctions, Observations suggested that protrusio n resulted from passive linear deformation in response to tensile stre ss exerted by centripetal contraction of the neighboring cell, The tim e dependence of cytoplasmic strain calculated from the displacements o f beads and vesicles was fit quantitatively by a Kelvin-Voight model f or a viscoelastic solid with a mean limiting strain of 0.58 and a mean strain rate of 4.3 x 10(-3) s(-1). In rare instances, the deforming c ell and its neighbor spontaneously became uncoupled, and recoil of the protruding margin was observed, The time dependence of strain during recoil also fit a Kelvin-Voight model with similar parameters, suggest ing that the kinetics of deformation primarily reflect the mechanical properties of the deformed cell rather than the contractile properties of its neighbor, The existence of mechanical coupling between adjacen t fibroblasts through adherens junctions and the viscoelastic response s of cells to tension transmitted directly from cell to cell are facto rs that must be taken into account to fully understand the role of fib roblasts in such biological processes as wound closure and extracellul ar matrix remodeling during tissue development.