Biophysical Journal
Volume 98, Issue 6, 17 March 2010, Pages 979-988
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Article
Force Generation in Lamellipodia Is a Probabilistic Process with Fast Growth and Retraction Events

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Abstract

Polymerization of actin filaments is the primary source of motility in lamellipodia and it is controlled by a variety of regulatory proteins. The underlying molecular mechanisms are only partially understood and a precise determination of dynamical properties of force generation is necessary. Using optical tweezers, we have measured with millisecond (ms) temporal resolution and picoNewton (pN) sensitivity the force-velocity (Fv) relationship and the power dissipated by lamellipodia of dorsal root ganglia neurons. When force and velocity are averaged over 3–5 s, the Fv relationships can be flat. On a finer timescale, random occurrence of fast growth and subsecond retractions become predominant. The maximal power dissipated by lamellipodia over a silica bead with a diameter of 1 μm is 10−16 W. Our results clarify the dynamical properties of force generation: i), force generation is a probabilistic process; ii), underlying biological events have a bandwidth up to at least 10 Hz; and iii), fast growth of lamellipodia leading edge alternates with local retractions.

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Vincent Torre's present address is International School for Advanced Studies (SISSA), Area Science Park, S.S.14, Q1 Bldg., Basovizza, Trieste-34149, Italy.