Showing papers by "James P. Butler published in 2005"
TL;DR: Both forced and spontaneous motions of microbeads tightly bound to the CSK of human muscle cells are reported, establishing a striking analogy between the behaviour of the living CSK and that of inert non-equilibrium systems, including soft glasses, but with important differences that are highly ATP-dependent.
Abstract: The cytoskeleton (CSK) is a crowded network of structural proteins that stabilizes cell shape and drives cell motions. Recent studies on the dynamics of the CSK have established that a wide variety of cell types exhibit rheology in which responses are not tied to any particular relaxation times and are thus scale-free. Scale-free rheology is often found in a class of materials called soft glasses, but not all materials expressing scale-free rheology are glassy (see plastics, wood, concrete or some metals for example). As such, the extent to which dynamics of the CSK might be regarded as glassy remained an open question. Here we report both forced and spontaneous motions of microbeads tightly bound to the CSK of human muscle cells. Large oscillatory shear fluidized the CSK matrix, which was followed by slow scale-free recovery of rheological properties (aging). Spontaneous bead motions were subdiffusive at short times but superdiffusive at longer times; intermittent motions reflecting nanoscale CSK rearrangements depended on both the approach to kinetic arrest and energy release due to ATP hydrolysis. Aging, intermittency, and approach to kinetic arrest establish a striking analogy between the behaviour of the living CSK and that of inert non-equilibrium systems, including soft glasses, but with important differences that are highly ATP-dependent. These mesoscale dynamics link integrative CSK functions to underlying molecular events, and represent an important intersection of topical issues in condensed matter physics and systems biology.
456 citations
TL;DR: The results demonstrate that the prestress in the cytoskeleton is crucial in mediating stress propagation to the nucleolus, with implications for direct mechanical regulation of nuclear activities and functions.
134 citations
TL;DR: Stiffness increased with frequency as a weak power law, and changes of friction paralleled those of stiffness until they approached a Newtonian viscous limit, which implies special constraints on the protein-protein interactions that dominate CSK mechanical properties.
Abstract: Although changes of cytoskeleton (CSK) stiffness and friction can be induced by diverse interventions, all mechanical changes reported to date can be scaled onto master relationships that appear to...
89 citations
TL;DR: This data indicates that minimum toe clearance and maximum angular inclination of the sole relative to the floor during the swing phase of gait and the maximum lateral sway of the trunk relative to lateral foot separation discriminate fallers from non‐fallers in the elderly.
Abstract: Background: To test the hypothesis that minimum toe clearance and maximum angular inclination of the sole relative to the floor during the swing phase of gait and the maximum lateral sway of the trunk relative to lateral foot separation discriminate fallers from non-fallers in the elderly.
Methods: We studied 25 community-dwelling elderly subjects with a history of two or more falls in the previous year and 31 age- and sex-matched controls with no such history. Studies were conducted in the Gait Laboratory, Tohoku University School of Medicine, Sendai, Japan. Subjects were asked to walk normally, during which time we made three-dimensional kinematic spatial and temporal gait measurements using a motion capturing system with reflective markers defining different segments of trunk and limbs.
Results: The toe clearance of fallers (12.0 ± 0.7 mm, mean ± SE) was significantly smaller than non-fallers (15.2 ± 1.0 mm) (P < 0.001). The maximal sole inclination of fallers (7.4 ± 0.8°) was significantly smaller than non-fallers (14.3 ± 0.9°) (P < 0.001). The lateral sway ratio (lateral excursion of trunk center relative to the mediolateral separation of the feet) was significantly larger in fallers (0.23 ± 0.01) compared with non-fallers (0.18 ± 0.01) (P < 0.002).
Conclusions: These results support the idea that impairment in toe clearance, maximal sole inclination and dynamic trunk sway reflect quantifiable mechanisms that may predispose elderly individuals to falling, and that these kinematic measurements may be clinically useful in identifying patients at risk of falling and monitoring changes in gait patterns, and may lead to effective interventions to prevent falls.
57 citations
TL;DR: This prototype device employs a simple, low‐cost electromagnet, with an open geometry that allows variation of the orientation of the imaging subject in a two‐dimensional plane to enable studies of human pulmonary physiology as a function of subject orientation.
Abstract: The human lung and its functions are extremely sensitive to gravity; however, the conventional high-field magnets used for most laser-polarized (3)He MRI of the human lung restrict subjects to lying horizontally. Imaging of human lungs using inhaled laser-polarized (3)He gas is demonstrated in an open-access very-low-magnetic-field (<5 mT) MRI instrument. This prototype device employs a simple, low-cost electromagnet, with an open geometry that allows variation of the orientation of the imaging subject in a two-dimensional plane. As a demonstration, two-dimensional lung images were acquired with 4-mm in-plane resolution from a subject in two orientations: lying supine and sitting in a vertical position with one arm raised. Experience with this prototype device will guide optimization of a second-generation very-low-field imager to enable studies of human pulmonary physiology as a function of subject orientation.
49 citations
TL;DR: It is concluded that mesothelial surfaces, sliding under physiological conditions, are protected from excessive shear by hydrodynamic pressures that increase separation of surfaces.
43 citations
TL;DR: In these behaviors, link length regulation, as described by the parameter s, was found to be crucial and all phenomena reported thus far in the literature were captured by this extremely simple network model.
Abstract: To account for cytoskeleton remodeling as well as smooth muscle length adaptation, here we represent the cytoskeleton as a two-dimensional network of links (contractile filaments or stress fibers) ...
26 citations
TL;DR: Bifurcating flow asynchrony in a simplified one-dimensional model finds unexpected richness and chaos in particle trajectories; almost all trajectories visit all spatial positions; surprisingly, there is complete mixing-the limiting concentration is spatially uniform.
19 citations