566 research outputs found
Néoformation pédogénétique d'une zéolite, la mordénite, associée aux carbonates de sodium dans une dépression interdunaire des bords du lac Tchad
Minéraux argileux et vermiculite-Al dans quelques sols et arènes des Vosges : hypothèse sur la néoformation des minéraux à 14JA
Cuirasses latéritiques et minéralisations aurifères de la région de Kangaba au Mali : cartographie, pétrographie, minéralogie, géochimie et télédétection : rapport de première phase
Equilibres entre minéraux et solutions : programmes de calcul appliqués à la prédiction de la salure des sols et des doses optimales d'irrigation
Néoformation d'une argile magnésienne dans les dépressions interdunaires du lac Tchad : application aux domaines de stabilité des phyllosilicates alumineux, magnésiens et ferrifères
Modeling actin filament reorganization in endothelial cells subjected to cyclic stretch
Hemodynamic forces affect endothelial cell morphology and function. In particular, circumferential cyclic stretch of blood vessels, due to pressure changes during the cardiac cycle, is known to affect the endothelial cell shape, mediating the alignment of the cells in the direction perpendicular to stretch. This change in cell shape proceeds a drastic reorganization at the internal level. The cellular scaffolding, mainly composed of actin filaments, reorganize in the direction which later becomes the cell's long axis. How this external mechanical stimulus is 'sensed' and transduced into the cell is still unknown. Here, we develop a mathematical model depicting the dynamics of actin filaments, and the influence of the cyclic stretch of the substratum based on the experimental evidence that external stimuli may be transduced inside the cell via transmembrane proteins which are coupled with actin filaments on the cytoplasmic side. Based on this view, we investigate two approaches describing the formulation of the transduction mechanisms involving the coupling between filaments and the membrane proteins. As a result, we find that the mechanical stimulus could cause the experimentally observed reorganization of the entire cytoskeleton simply by altering the dynamics of the filaments connected with the integral membrane proteins, as described in our model. Comparison of our results with previous studies of cytoskeletal dynamics reveals that the cytoskeleton, which, in the absence of the effect of stretch would maintain its isotropic distribution, slowly aligns with the precise direction set by the external stimulus. It is found that even a feeble stimulus, coupled with a strong internal dynamics, is sufficient to align actin filaments perpendicular to the direction of stretc
Interpreting Photoactive Fluorescence Microscopy Measurements of Steady-State Actin Dynamics
Biophysical Journal, 1995A continuum model describing the steady-state actin dynamics of the cytoskeleton of living cells Has been
developed to aid in the interpretation of photoactivated fluorescence experiments. In a simplified cell geometry, the model
assumes uniform concentrations of cytosolic and cytoskeletal actin throughout the cell and no net growth of either pool. The
spatiotemporal evolution of the fluorescent actin population is described by a system of two coupled linear partial-differential
equations. An analytical solution is found using a Fourier-Laplace transform and important limiting cases relevant to the
design of experiments are discussed. The results demonstrate that, despite being a complex function of the parameters, the
fluorescence decay in photoactivated fluorescence experiments has a biphasic behavior featuring a short-term decay
controlled by monomer diffusion and a long-term decay governed by the monomer exchange rate between the polymerized
and unpolymerized actin pools. This biphasic behavior suggests a convenient mechanism for extracting the parameters
governing the fluorescence decay from data records. These parameters include the actin monomer diffusion coefficient,
filament turnover rate, and ratio of polymerized to unpolymerized actin
GĂ©ochimie d'un bassin versant au Maroc oriental : Ă©volution des argiles dans les sols des montagnes et des plaines de la basse Moulouya
- …