Directed cell migration is essential in both physiological and pathological situations. Many guidance cues have been extensively investigated in the past decades, to be able to regulate directional cell migration, including chemical, physiological and haptotactic cues. In the past years, we have focused on the roles of physiological electric field in the guidance of directed cell migration. It is well accepted that physiological electric fields exist both extracellularly and intracellularly with different functions, and interestingly, endogenous EFs exist in not only physiological but also pathological events. For instance, the existence of a small current in developing embryos which is also known as the endogenous electric field has been tested, such as the blastopore in Xenopus, chicken embryos, and etc. It has been also demonstrated that endogenous electric fields exist at the wound edges of injured cornea and skin. Physiological electric field is among many other guidance cues controlling an important cellular response – directed cell migration in response to stimuli, a phenomenon named electrotaxis or galvanotaxis. We and others have extensively demonstrated that physiological EFs could control directional cell migration, and that several signalling pathways are required for the regulation of such event. In the current study, we used Dictyostelium model to further explore the molecular and genetic mechanisms of how electrotaxis is controlled, by extensively investigating candidate molecules and genes in such regulation. We found that PI3K, PTEN and Ras signalling pathways are largely involved in the regulation of electrotaxis, Ras plays more dominant roles in this event in comparison with PI3K and PTEN, which only partially contributed towards the electrotactic response of the Dictyostelium cells. Asymmetric redistribution of signalling molecules are shown to play an essential role in the initiation and maintenance of the electrotactic response of the cells.

Macrophages are key cells during inflammation and repair. Their activity is highly varied and requires precise regulation. The characterisation of cues coordinating macrophage functions has focussed on chemical and biological soluble mediators. Little is known about their responses to physical stimuli, in particular electric fields (EF) that are generated naturally in wounded tissue and infected tissue. Importantly, EFs are known to accelerate wound healing and limit infection but the mechanisms of this remain poorly understood. To address this gap in understanding, this study tested how key properties of human monocyte-derived macrophages are regulated by applied EFs equivalent to physiological EF strengths generated naturally. Using live-cell video microscopy, we show macrophage migration is directed anodally by EFs as low as 5 mV/mm and is EF-strength dependent, with effects peaking around 300 mV/mm. In contrast, monocytes, as macrophage-precursors, migrate in the opposite, cathodal direction. Strikingly, we show for the first time that EFs significantly enhance macrophage phagocytic uptake of a variety of targets, including carboxylate beads, apoptotic neutrophils and the nominal opportunist pathogen Candida albicans, all of which engage different classes of surface receptors. These EF-induced functional changes are accompanied by clustering of phagocytic receptors, enhanced PI3K and ERK activation, mobilization of intracellular calcium and actin polarization. EFs also selectively modulate cytokine production and augment effects of conventional polarising stimuli on cytokine secretion. Taken together, electrical signals have been identified as major contributors to the co-ordination and regulation of important human macrophage functions, including those essential for microbial clearance and healing. Our results open up a new area of research into effects of naturally occurring and clinically-applied EFs in conditions where macrophage activity is crucial.

Wong Yuen-yee. / Thesis submitted in: August 2005. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2006. / Includes bibliographical references (leaves 121-125). / Abstracts in English and Chinese. / THESIS COMMITTEE --- p.ii / ABSTRACT --- p.iii / 摘要 --- p.iv / ACKNOWLEDGEMENTS --- p.v / TABLE OF CONTENT --- p.vi / LIST OF TABLES --- p.viii / LIST OF FIGURES --- p.xi / Chapter Chapter 1 --- Introduction --- p.1 / Chapter Chapter 2 --- Quantum Mechanical Background --- p.9 / Chapter 2.1 --- Molecular energy operator and the Born-Oppenheimer approximation --- p.9 / Chapter 2.2 --- Electronic wavefunctions --- p.16 / Chapter 2.3 --- Vibrational wavefunctions --- p.22 / Chapter 2.4 --- Rotational wave function --- p.28 / Chapter 2.5 --- Tunneling Phenomenon --- p.31 / Chapter Chapter 3 --- Implementation --- p.35 / Chapter 3.1 --- Inversion potential --- p.37 / Chapter 3.2 --- Zero-field vibrational wavefunctions --- p.39 / Chapter 3.3 --- Zero-field rovibrational levels --- p.43 / Chapter 3.4 --- Stark energy and rovibrational levels in DC fields --- p.49 / Chapter 3.5 --- Transition dipole moments and intensities calculations --- p.52 / Chapter Chapter 4 --- Results and Discussions --- p.57 / Chapter 4.1 --- "Inversion potentials, levels, and energies" --- p.57 / Chapter 4.2 --- Rovibrational levels and spectrum at zero-field --- p.70 / Chapter 4.3 --- Rovibrational spectrum in DC fields --- p.83 / Chapter 4.3.1 --- Localization of vibrational wavefunctions --- p.83 / Chapter 4.3.2 --- Rovibrational energies and spectra --- p.89 / Chapter 4.4 --- Discussion --- p.118 / REFERENCE --- p.121

Ionospheric disturbance electric fields of magnetospheric origin play an important role in determining the global morphology and dynamics of the ionosphere of the Earth. In this work, we present a number of numerical simulations of the transient electric fields in the middle and inner magnetosphere and the ionosphere equatorward of the auroral zone caused by idealized changes in the magnetospheric driving parameters. For these studies, we u se the Rice Convection Model (RCM), a large computer code of the magnetosphere-ionosphere coupling which consistently computes the electric fields, currents, and plasma densities in the magnetosphere and the electric field and currents in the ionosphere in the quasi-static slow-flow approximation. We made substantial upgrades to the code, which include a module computing realistic solar EDY-produced ionospheric conductances and a new potential solver. Our upgraded version of the RCM also includes a time - varying magnetospheric magnetic field and a self-consistently estimated auroral zone. We first discuss numerical problems encountered in modeling electrodynamics of convection with a time-varying magnetic field, realistic ionospheric conductances, and a self-consistent auroral zone, and our solutions to those difficulties. We then present a number of "computer experiments" with the new version of the RCM with idealized changes in the magnetospheric parameters such as sudden changes in the cross polar cap potential drop, magnetic field reconfiguration corresponding to the overall changes in the high-latitude convection, as well as rotations of the electric field on the polar cap boundary. Prompt penetration ionospheric electric fields simulated with the upgraded RCM are shown to be consistent with the previous simulations. The new simulations and their results are discussed in the context of (1) possible contribution to the variability of the ionospheric electric fields, and (2) role of time-varying magnetic field on the characteristic lifetimes of prompt penetration electric fields at subauroral, middle, and low latitudes.

Thesis (Ph.D.) -- University of Texas at Arlington, 2009.

Thesis (Ph. D.)--University of Oklahoma, 1997. / Includes bibliographical references (leaves 75-78).

In this thesis, three specific research contributions to the use of non-uniform electric field driven colloidal assembly are described. The first relates to experimental work using dielectrophoretic and electrohydrodynamic forces (electroosmosis) to shape three-dimensional colloidal structures. Formation and stabilization of close-packed three-dimensional structures from colloidal silica was demonstrated, using gelation of pluronic F-127 to preserve medium structure against suspension evaporation. Stabilization of ordered structures was shown to be a significant challenge, with many of the conventional techniques for immobilizing colloidal crystals being ineffective. Secondly, the significance of electrohydrodynamic flows resulting from electric and particle concentration (entropic) gradients during the assembly process was demonstrated using numerical simulations based on a thermodynamic framework. These simulations, as well as experimental validation of assembly and the presence of fluid flows, showed that assuming equilibrium behavior (stationary fluid flow), a common assumption for most modelling work to date in these systems, is inappropriate at all but the most dilute concentration cases. Finally, the relevance of multiparticle effects on electric-field induced phase transitions of dielectric colloids was demonstrated. The effect of multiparticle/multiscattering effects on the suspension permittivity were accounted for using semi-empirical continuum permittivity formulations which have been previously shown to describe a wide variety of solid packing structures, including face-centered cubic and other colloidal crystal structures. It was shown that multiparticle effects have a significant impact on both the coexistence (slow phase separation) and spinodal (fast phase separation) behavior of dielectric suspensions, which has not been demonstrated to date using a continuum framework. / Thesis (Ph.D, Chemical Engineering) -- Queen's University, 2012-01-30 14:17:23.747

No description available.

I have investigated whether or not neurotrophic factors can alter the effects of an applied electric field on neurite growth. A direct current electric field (150mV/mm) applied for 5 hours affected the growth of dissociated cells from the neutral tube of stage 20 <I>Xenopus laevis. </I>Neurites turned and grew to the cathode, showed a differential rate of growth, with cathodal-facing neurites growing faster than those facing the anode, and exhibited a polarised branching pattern, with the majority of branches emanating from the cathodal-facing side of the neurite. Exposure of neurites to the neurotrophins neurotrophin 3 (NT-3; 50ng/ml and 100ng/ml), brain derived neurotrophic factor (BDNF; 50ng/ml and 100ng/ml) and neurotrophin 4 (NT-4; 100ng/ml) lowered the threshold field strength necessary to elicit a turning response to 100mV/mm. Only BDNF (100ng/ml) enhanced cathodal orientation at 150mV/mm, with neurites turning three times as far as in the field alone. Additionally, in the presence of these neurotrophins the threshold field that evoked a differential rate of growth and polarised branching was also lowered to 100mV/mm. Neurite turning did not occur in a field of 100mV/mm in the presence of 50ng/ml nerve growth factor (NGF), 100ng/ml ciliary neurotrophic factor (CNTF) or 50ng/ml glial-cell-line derived neurotrophic factor (GDNF), or when the Trk receptor tyrosine kinase inhibitors K-252a and K-252b were added concomitantly with 50ng/ml NT-3. <I>Xenopus </I>growth cones release acetylcholine (Ach) spontaneously. This is enhanced by NT-3, BDNF, NT-4. Nicotinic Ach receptor antagonists abolish field-induced cathodal turning, thus Ach release may be crucial for this response. The neurotrophins NT-3, BDNF and NT-4 may therefore modulate field-directed nerve growth because they enhance Ach release. Interactions <I>in vivo,</I> where neurotrophins and electric fields co-exist, would increase the efficacy of endogenous electric fields as modulators of nerve growth.

Thesis (Ph. D.)--Brigham Young University. Dept. of Chemistry and Biochemistry, 2007. / Includes bibliographical references.