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Force-velocity curves of motor proteins cooperating in vivo.

ABSTRACT: Motor proteins convert chemical energy into work, thereby generating persistent motion of cellular and subcellular objects. The velocities of motor proteins as a function of opposing loads have been previously determined in vitro for single motors. These single molecule "force-velocity curves" have been useful for elucidating motor kinetics and for estimating motor performance under physiological loads due to, for example, the cytoplasmic drag force on transported organelles. Here we report force-velocity curves for single and multiple motors measured in vivo. Using motion enhanced differential interference contrast (MEDIC) movies of living NT2 (neuron-committed teratocarcinoma) cells at 37 degrees C, three parameters were measured--velocity (v), radius (a), and effective cytoplasmic viscosity (eta')--as they applied to moving vesicles. These parameters were combined in Stokes' equation, F = 6piaeta'v, to determine the force, F, required to transport a single intracellular particle at velocity, v. In addition, the number of active motors was inferred from the multimodal pattern seen in a normalized velocity histogram. Using this inference, the resulting in vivo force-velocity curve for a single motor agrees with previously reported in vitro single motor force-velocity curves. Interestingly, however, the curves for two and three motors lie significantly higher in both measured velocity and computed force, which suggests that motors can work cooperatively to attain higher transport forces and velocities.

SUBMITTER: Shtridelman Y

PROVIDER: S-EPMC2561921 | biostudies-literature | 2008

REPOSITORIES: biostudies-literature

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Force-velocity curves of motor proteins cooperating in vivo.

Shtridelman Yuri Y Cahyuti Thomas T Townsend Brigitte B DeWitt David D Macosko Jed C JC

Cell biochemistry and biophysics 20080101 1

Motor proteins convert chemical energy into work, thereby generating persistent motion of cellular and subcellular objects. The velocities of motor proteins as a function of opposing loads have been previously determined in vitro for single motors. These single molecule "force-velocity curves" have been useful for elucidating motor kinetics and for estimating motor performance under physiological loads due to, for example, the cytoplasmic drag force on transported organelles. Here we report forc ...[more]

PMID: 18696014

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Project description:BackgroundThe collection and analysis of Atomic Force Microscopy force curves is a well-established procedure to obtain high-resolution information of non-topographic data from any kind of sample, including biological specimens. In particular, these analyses are commonly employed to study elasticity, stiffness or adhesion properties of the samples. Furthermore, the collection of several force curves over an extended area of the specimens allows reconstructing maps, called force volume maps, of the spatial distribution of the mechanical properties. Coupling these maps with the conventional high-resolution topographic reconstruction of the sample's surface, provides a deeper insight on the sample composition from the structural and nanomechanical point of view.ResultsIn this paper we present the open source software package FC_analysis that automatically analyses single force curves or entire force volume maps to yield the corresponding elasticity and deformability images. The principal characteristic of the FC_analysis is a large adaptability to the various experimental setups and to different analysis methodologies. For instance, the user can provide custom values for the detector sensitivity, scanner-z sensitivity, cantilever's elastic constant and map's acquisition modality and can choose between different analysis methodologies. Furthermore, the software allows the optimization of the fitting parameters and gives direct control on each step of the analysis procedure. Notably, to overcome a limitation common to many other analysis programs, FC_analysis can be applied to a rectangular portion of the image, allowing the analysis of inhomogeneous samples. Finally, the software allows reconstructing a Young's modulus map at different penetration depths, enabling the use of modern investigation tools such as the force tomography.ConclusionsThe FC_analysis software aims to become a useful tool for the analysis of force curves maps collected using custom or commercial Atomic Force Microscopes, and is especially useful in those cases for which the producer doesn't release a dedicated software.

Project description:Changes in muscle shape could play an important role during contraction allowing to circumvent some limits imposed by the fascicle force-velocity (F-V) and power-velocity (P-V) relationships. Indeed, during low-force high-velocity contractions, muscle belly shortening velocity could exceed muscle fascicles shortening velocity, allowing the muscles to operate at higher F-V and P-V potentials (i.e., at a higher fraction of maximal force/power in accordance to the F-V and P-V relationships). By using an ultrafast ultrasound, we investigated the role of muscle shape changes (vastus lateralis) in determining belly gearing (muscle belly velocity/fascicle velocity) and the explosive torque during explosive dynamic contractions (EDC) at angular accelerations ranging from 1000 to 4000°.s-2. By means of ultrasound and dynamometric data, the F-V and P-V relationships both for fascicles and for the muscle belly were assessed. During EDC, fascicle velocity, belly velocity, belly gearing, and knee extensors torque data were analysed from 0 to 150 ms after torque onset; the fascicles and belly F-V and P-V potentials were thus calculated for each EDC. Absolute torque decreased as a function of angular acceleration (from 80 to 71 Nm, for EDC at 1000 and 4000°.s-1, respectively), whereas fascicle velocity and belly velocity increased with angular acceleration (P < 0.001). Belly gearing increased from 1.11 to 1.23 (or EDC at 1000 and 4000°.s-1, respectively) and was positively corelated with the changes in muscle thickness and pennation angle (the changes in latter two equally contributing to belly gearing changes). For the same amount of muscle's mechanical output (force or power), the fascicles operated at higher F-V and P-V potential than the muscle belly (e.g., P-V potential from 0.70 to 0.56 for fascicles and from 0.65 to 0.41 for the muscle belly, respectively). The present results experimentally demonstrate that belly gearing could play an important role during explosive contractions, accommodating the largest part of changes in contraction velocity and allowing the fascicle to operate at higher F-V and P-V potentials.

Project description:The aim of the study was to examine the test-retest reliability and agreement across methods for assessing individual force-velocity (FV) profiles of the lower limbs in athletes. Using a multicenter approach, 27 male athletes completed all measurements for the main analysis, with up to 82 male and female athletes on some measurements. The athletes were tested twice before and twice after a 2- to 6-month period of regular training and sport participation. The double testing sessions were separated by ~1 week. Individual FV-profiles were acquired from incremental loading protocols in squat jump (SJ), countermovement jump (CMJ) and leg press. A force plate, linear encoder and a flight time calculation method were used for measuring force and velocity during SJ and CMJ. A linear regression was fitted to the average force and velocity values for each individual test to extrapolate the FV-variables: theoretical maximal force (F0), velocity (V0), power (Pmax), and the slope of the FV-profile (SFV). Despite strong linearity (R2>0.95) for individual FV-profiles, the SFV was unreliable for all measurement methods assessed during vertical jumping (coefficient of variation (CV): 14-30%, interclass correlation coefficient (ICC): 0.36-0.79). Only the leg press exercise, of the four FV-variables, showed acceptable reliability (CV:3.7-8.3%, ICC:0.82-0.98). The agreement across methods for F0 and Pmax ranged from (Pearson r): 0.56-0.95, standard error of estimate (SEE%): 5.8-18.8, and for V0 and SFV r: -0.39-0.78, SEE%: 12.2-37.2. With a typical error of 1.5 cm (5-10% CV) in jump height, SFV and V0 cannot be accurately obtained, regardless of the measurement method, using a loading range corresponding to 40-70% of F0. Efforts should be made to either reduce the variation in jumping performance or to assess loads closer to the FV-intercepts. Coaches and researchers should be aware of the poor reliability of the FV-variables obtained from vertical jumping, and of the differences across measurement methods.

Project description:BackgroundThe theoretical maximum force (F0), velocity (V0), and power (Pmax) of athletes calculated from the relationship between force and velocity (F-V relationship) and the slope of the F-V relationship, reflect their competitive and training activity profiles. Evaluating the F-V relationship of athletes facilitates categorizing the profiles of dynamic muscle functions in relation to long-term sport-specific training. For gymnastics, however, no studies have tried to examine the profiles of F-V relation and power output for upper limb muscles in relation to the muscularity, while the use of the upper extremities in this sport is very unique as described earlier.PurposeIt was hypothesized that the F-V relationship of the elbow flexion in gymnasts might be characterized by low capacity for generating explosive force, notably in terms of the force normalized to muscle size.MethodsThe F0, V0, and Pmax derived from the force-velocity relationship during explosive elbow flexion against six different loads (unloaded condition, 15, 30, 45, 60, and 75% of maximal voluntary isometric elbow flexion force (MVFEF)) for 16 gymnasts (GYM) and 22 judo athletes (JD). F0 and Pmax were expressed as values relative to the cross-sectional area index (CSAindex) of elbow flexors (F0/CSAindex and Pmax/CSAindex, respectively), which was calculated from muscle thickness in the anterior upper arm. The electromyogram (EMG) activities of the biceps brachii (BB) during the maximal isometric and dynamic tasks were also determined.ResultsThere were no significant differences in CSAindex of elbow flexors between GYM and JD. MVFEF/CSAindex for GYM was significantly lower than that for JD. Force was linearly associated with velocity in the dynamic elbow flexion for all the participants (r = - 0.997 to -0.905 for GYM, r = - 0.998 to -0.840 for JD). F0, F0/ CSAindex, V0, Pmax, Pmax/CSAindex, and MVFEF were significantly lower in GYM than in JD. The activity levels of BB during the dynamic tasks tended to be lower in GYM than in JD at load of <45%MVC.ConclusionGymnasts cannot generate explosive elbow flexion force corresponding to their muscle size. This may be due to low neuromuscular activities during the maximal dynamic tasks against relatively low loads.

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Force-velocity curves of motor proteins cooperating in vivo.

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Force-velocity curves of motor proteins cooperating in vivo.

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