Actin and Myosin Remodeling in the A7r5 Smooth Muscle Cell

Active remodeling of the cytoskeleton has been proposed to contribute to the low energy cost and maintenance of the sustained contraction in smooth muscle. Using confocal microscopy and standard immunohistochemical techniques, direct observation of actin remodeling was studied in the contracting A7r5 cell in response to the diacylglycerol (DAG) analog phorbol 12, 13 dibutyrate (PDBu). -actin was shown to exist in the resting cell as parallel stress cables that extend across the cell. Stimulation by PDBu resulted in a sustained contraction that occurred in approximately eighty-five percent of the A7r5 cells. The initial contraction was not uniform, but primarily occurred in the axis parallel to the ?-actin cables. During the latter portion of contraction shortening occurred in all axis. During contraction, the cells shortened without apparent compression of the ?-actin fibers or new cable formation, suggesting that ?-actin fibers undergo active remodeling during contraction. Treatment of the cells with cytochalasin resulted in dissolution of fibers in the central region of the cell and elongation of precontracted cells in the axis parallel to the ?-actin fibers, suggesting that the ?-actin cytoskeleton may serve to hold the cell in the contracted state. In unstimulated cells, ?-actin exists as series of stress fibers similar in appearance to ?-actin fibers. In contrast, within ten minutes of PDBu stimulation ?-actin disassembled and reassembled into intensely-staining column-like structures that extend from the cell?s base. The ?-actin column-like structures demonstrate a strong colocalization with ?-actinin suggesting that they may be homologous to dense bodies in differentiated smooth muscle. Smooth muscle myosin also undergoes remodeling, in a manner very similar to ?-actin. Dual immunostaining for ?-actin and smooth muscle myosin indicate a strong colocalization of the two proteins in the resting cell. However, following PDBu stimulation there was a partial dissociation of myosin from ?-actin. Treatment of cells with cytochalasin B or dissolution of the ?-actin fibers with thapsigargin resulted in similar patterns of staining for ?-actin and myosin. This suggests that myosin is in association with ?-actin and follows changes in ?-actin structure during contraction. This work suggests that the ?- and ?-actin domains in the A7r5 cells undergo specific remodeling in A7r5 cells, and suggests a model in which ?-actin filaments undergo remodeling to hold the cell in the shortened state at low energy cost while ?-actin and myosin remodel into a configuration that allows maximal mechanical advantage for contraction

Partial Characterization of Na+, K+-ATPase and its Gill and Antennal Gland Osmoregulatory Role in the Crayfish, Orconectes putnami

A thesis presented to the faculty of the College of Science and Technology at Morehead State University in partial fulfillment of the requirements for the Degree of Master of Science in Biology by Michael E. Fultz on August 1, 1997

Raman spectrometry study of phonon anharmonicity of hafnia at elevated temperatures

Raman spectra of monoclinic hafnium oxide (HfO_2) were measured at temperatures up to 1100 K. Raman peak shifts and broadenings are reported. Phonon dynamics calculations were performed with the shell model to obtain the total and partial phonon density of states, and to identify the individual motions of Hf and O atoms in the Raman modes. Correlating these motions to the thermal peak shifts and broadenings, it was found that modes involving changes in oxygen-oxygen bond length were the most anharmonic. The hafnium-dominated modes were more quasiharmonic and showed less broadening with temperature. Comparatively, the oxygen-dominated modes were more influenced by the cubic term in the interatomic potential than the hafnium-dominated modes. An approximately quadratic correlation was found between phonon-line broadening and softening

Vibrational and electronic entropy of β-cerium and γ-cerium measured by inelastic neutron scattering

Time-of-flight (TOF) inelastic neutron-scattering spectra were measured on β-cerium (double hcp) and γ-cerium (fcc) near the phase-transition temperature. Phonon densities of states (DOS) and crystal-field levels were extracted from the TOF spectra. A softening of the phonon DOS occurs in the transition from β- to γ-cerium, accounting for an increase in vibrational entropy of ΔSvibγ-β=(0.09±0.05)kB/atom. The entropy calculated from the crystal-field levels and a fit to calorimetry data from the literature were significantly larger in β-cerium than in γ-cerium below room temperature, but the difference was found to be negligible at the experimental phase-transition temperature. A contribution to the specific heat from Kondo spin fluctuations was consistent with the quasielastic magnetic scattering, but the difference between phases was negligible. To be consistent with the latent heat of the β-γ transition, the increase in vibrational entropy at the phase transition may be accompanied by a decrease in electronic entropy not associated with the crystal-field splitting or spin fluctuations. At least three sources of entropy need to be considered for the β-γ transition in cerium

Development of a Cell Culture System to Examine the Acclimation, Contraction, and Cytoskeletal Remodeling of A7r5 Smooth Muscle Cells to Microgravity

https://scholarworks.moreheadstate.edu/student_scholarship_posters/1020/thumbnail.jp

Effect of Microgravity on the Contraction and Cytoskeletal Remodeling of A7r5 Smooth Muscle Cells

Smooth muscle presents several unique contractile properties when compared to striated muscle. Data suggests that differential remodeling of the alpha-actin and beta-actin and the regulation of such remodeling may play an essential role in smooth muscle contraction. At rest both alpha- and beta-actin both exhibit a cable-like appearance. During contraction, alpha-actin appears to undergo significant remodeling with dissolution on the majority of the cables and the formation of podosomes where it demonstrates co-localization with myosin while beta-actin retains a cable-like appearance. While the remodeling of the two actin domains has been characterized under normal gravity little is known regarding cytoskeletal dynamics in A7r5 smooth muscle cells. A7r5 cells will be subjected to the microgravity environment of the International Space Station. We speculate that the absence of gravity as an organizing force on biological structures may produce different effects than what is observed on Earth. In collaboration with SpaceTango Inc., a cell culturing module has been engineered that will allow the cells to ascend into space and maintain homeostasis while on orbit. The module will also administer phorbol ester, a contractile stimulant, followed by acetone to “fix” the cells in their contracted state so observations can be made about the aforementioned processes when they return from orbit

MCViNE -- An object oriented Monte Carlo neutron ray tracing simulation package

MCViNE (Monte-Carlo VIrtual Neutron Experiment) is a versatile Monte Carlo (MC) neutron ray-tracing program that provides researchers with tools for performing computer modeling and simulations that mirror real neutron scattering experiments. By adopting modern software engineering practices such as using composite and visitor design patterns for representing and accessing neutron scatterers, and using recursive algorithms for multiple scattering, MCViNE is flexible enough to handle sophisticated neutron scattering problems including, for example, neutron detection by complex detector systems, and single and multiple scattering events in a variety of samples and sample environments. In addition, MCViNE can take advantage of simulation components in linear-chain-based MC ray tracing packages widely used in instrument design and optimization, as well as NumPy-based components that make prototypes useful and easy to develop. These developments have enabled us to carry out detailed simulations of neutron scattering experiments with non-trivial samples in time-of-flight inelastic instruments at the Spallation Neutron Source. Examples of such simulations for powder and single-crystal samples with various scattering kernels, including kernels for phonon and magnon scattering, are presented. With simulations that closely reproduce experimental results, scattering mechanisms can be turned on and off to determine how they contribute to the measured scattering intensities, improving our understanding of the underlying physics.Comment: 34 pages, 14 figure

AtomSim: web-deployed atomistic dynamics simulator

AtomSim, a collection of interfaces for computational crystallography simulations, has been developed. It uses forcefield-based dynamics through physics engines such as the General Utility Lattice Program, and can be integrated into larger computational frameworks such as the Virtual Neutron Facility for processing its dynamics into scattering functions, dynamical functions etc. It is also available as a Google App Engine-hosted web-deployed interface. Examples of a quartz molecular dynamics run and a hafnium dioxide phonon calculation are presented