A MICROMACHINED DEVICE PROVIDES A NEW BEND ON FIBROBLAST TRACTION FORCES

We have measured the traction forces generated by fibroblasts using a novel micromachined device that is capable of determining the subcellu lar forces generated by individual adhesive contacts, The front of mig rating fibroblasts produced intermittent rearward forces whereas tile tail produced larger forward directed forces, None of the forces were steady; they all had periodic fluctuations, The transition between for ward and rearward traction forces occurred at tile nucleus, not at the rear of the cell or the border between the endoplasm and the ectoplas m, We propose that the coupling of lamella extensions to fluctuating r earward tractions in front of the nuclear region move the front of a f ibroblast forward, while force-facilitated release of rear adhesive co ntacts and anterior-directed tractions allow the region behind the nuc leus to advance.