Traction forces in locomoting cells

Abstract

A means of determining quantitative maps of the tractions exerted by locomoting cells on a substratum has been developed. This method is similar to the Harris silicone substratum assay [Harris et al., 1980: Science 208:177-179], but uses an improved non-wrinkling film that deforms more predictably in response to traction forces. The method also utilizes a mathematical analysis of rubber deformation to produce the final map of the distribution of tractions. The resulting maps consistently showed that fish keratocytes exert a steady-state "pinching" on the substratum, perpendicular to the cell's direction of locomotion. No significant rearward tractions were detected at or near the front edge of the cell. Likewise, no significant forward tractions associated with peeling of adhesions were found at the back of the cell. A second assay uses deflection of a lightly attached glass microneedle to measure the total force exerted by locomoting cells. Forces of approximately 4.5 x 10(-3) dyn were required to "stall" locomoting keratocytes. The implications of these findings for cell movement are discussed.

Alpha-Smooth Muscle Actin Expression Upregulates Fibroblast Contractile Activity

“…It is conceivable that wrinkle-producing fibroblasts exert only the minimum force necessary to deform these weak surfaces; therefore, the use of elastomers with gradually increasing stiffness is crucial to determine their maximum contractile potential. Highly compliant elastomers have been wrinkled by a large proportion of ␣-SMAnegative fibroblasts consistent with the wrinkling capability of numerous cell types (Lee et al, 1994;Oliver et al, 1995). With the use of stiffer substrates, we determined a threshold of ϳ4 N that discriminates between these relatively weak traction forces and higher contractile forces (Roy et al, 1999); this threshold is only surpassed by ␣-SMA-positive fibroblasts.…”

“…A second stiff needle (Ն50 N/ m) was used to fix the substrate at a distance of 200 m, simulating the substrate-pinching of bipolar cells. The force required to produce first wrinkles on different silicone substrates was calculated from the flexible needle stiffness ( N/ m) and deflection ( m; Oliver et al, 1995) on 15 different regions. LFs were then grown on these substrates and immunostained, and the percentage of wrinkling cells of ␣-SMA-positive LFs and of ␣-SMA-negative LFs were calculated separately as described above.…”

Keratocytes Generate Traction Forces in Two Phases

“…Traction forces during keratocyte locomotion were first studied by Jacobson and colleagues (Lee et al, 1994;Oliver et al, 1995;Dembo et al, 1996) with the use of a modification of the method developed by Harris et al (1980) in which cell forces applied to silicone rubber substrata produce deformations visible in the light microscope. Lee et al (1994) were able to fabricate elastic substrata with higher compliance than those used in earlier studies on fibroblasts (Harris et al, 1980), allowing lower forces to be detected.…”

“…Lee et al (1994) were able to fabricate elastic substrata with higher compliance than those used in earlier studies on fibroblasts (Harris et al, 1980), allowing lower forces to be detected. In addition, strain in the elastic substratum was quantified by monitoring the movements of markers incorporated into its surface (Harris, 1984;Lee et al, 1994;Oliver et al, 1995;Dembo et al, 1996) rather than wrinkles, as had been used originally (Harris et al, 1980). Their results showed that lateral forces, directed inward toward the center of the cell, were dominant during forward locomotion (Lee et al, 1994;Oliver et al, 1995).…”

Power transduction of actin filaments ratcheting in vitro against a load

“…However, the stalling force of a filament, at which the elongation velocity drops to zero, could be estimated to a few piconewtons (6)(7)(8). Comparatively, forces of a few nanonewtons are required to stall the migration of cells (9,10) or Listeria comet tails (11). This difference of three orders of magnitude points to the need for a large number of cooperating filaments to generate high forces in protrusive structures.…”