Papers by Marshal Porterfield
PLANT PHYSIOLOGY, 2007
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Zygote, Dec 1, 1999
The physiology of the early embryo may be indicative of embryo vitality and therefore methods for... more The physiology of the early embryo may be indicative of embryo vitality and therefore methods for non-invasively monitoring physiological parameters from embryos could improve preimplantation diagnoses. The self-referencing electrophysiological technique is capable of non-invasive measurement of the physiology of individual cells by monitoring the movement of ions and molecules between the cell and the surrounding media. Here we use this technique to monitor gradients of calcium, potassium, oxygen and hydrogen peroxide around individual mouse preimplantation embryos. The calcium-sensitive electrode in self-referencing mode identified a region of elevated calcium concentration (approximately 0.25 pmol) surrounding each embryo. The calcium gradient surrounding embryos was relatively steep, such that the region of elevated calcium extended into the medium only 4 microns from the embryo. By contrast, using an oxygen-sensitive electrode an extensive gradient of reduced dissolved oxygen concentration was measured surrounding the embryo and extended tens of micrometres into the medium. A gradient of neither potassium nor hydrogen peroxide was observed around unperturbed embryos. We also demonstrate that monitoring the physiology of embryos using the self-referencing technique does not compromise their subsequent development. Blastocyts studied with the self-referencing technique implanted and developed to term at the same frequency as did unexamined, control embryos. Therefore, the self-referencing electrode provides a valuable non-invasive technique for studying the physiology and pathophysiology of individual embryos without hindering their subsequent development.
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The Journal of neuroscience : the official journal of the Society for Neuroscience, 2001
An early step in repair of the leech CNS is the appearance of endothelial nitric oxide synthase (... more An early step in repair of the leech CNS is the appearance of endothelial nitric oxide synthase (eNOS) immunoreactivity and NOS activity, but coincident generation of NO at the lesion after injury has not been shown. This is important because NO can regulate microglial cell motility and axon growth. Indirect measurement of NO with the standard citrulline assay demonstrated that NO was generated within 30 min after nerve cord injury. A polarographic NO-selective self-referencing microelectrode that measures NO flux noninvasively was developed to obtain higher spatial and temporal resolution. With this probe, it was possible to demonstrate that immediately after the leech CNS was injured, NO left the lesion with a mean peak efflux of 803 +/- 99 fmol NO cm(-2) sec(-1). NO efflux exponentially declined to a constant value, as described through the equation f(t) = y(o) + ae(-t/tau), with tau = 117 +/- 30 sec. The constant y(o) = 15.8 +/- 4.5 fmol cm(-2) represents a sustained efflux of N...
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World Environmental and Water Resources Congress 2013, 2013
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Zygote, 2000
The physiology of the early embryo may be indicative of embryo vitality and therefore methods for... more The physiology of the early embryo may be indicative of embryo vitality and therefore methods for non-invasively monitoring physiological parameters from embryos could improve preimplantation diagnoses. The self-referencing electrophysiological technique is capable of non-invasive measurement of the physiology of individual cells by monitoring the movement of ions and molecules between the cell and the surrounding media. Here we use this technique to monitor gradients of calcium, potassium, oxygen and hydrogen peroxide around individual mouse preimplantation embryos. The calcium-sensitive electrode in self-referencing mode identified a region of elevated calcium concentration (approximately 0.25 pmol) surrounding each embryo. The calcium gradient surrounding embryos was relatively steep, such that the region of elevated calcium extended into the medium only 4 microns from the embryo. By contrast, using an oxygen-sensitive electrode an extensive gradient of reduced dissolved oxygen concentration was measured surrounding the embryo and extended tens of micrometres into the medium. A gradient of neither potassium nor hydrogen peroxide was observed around unperturbed embryos. We also demonstrate that monitoring the physiology of embryos using the self-referencing technique does not compromise their subsequent development. Blastocyts studied with the self-referencing technique implanted and developed to term at the same frequency as did unexamined, control embryos. Therefore, the self-referencing electrode provides a valuable non-invasive technique for studying the physiology and pathophysiology of individual embryos without hindering their subsequent development.
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The Plant Journal, 2010
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Planta, 2011
In single-celled spores of the fern Ceratopteris richardii, gravity directs polarity of developme... more In single-celled spores of the fern Ceratopteris richardii, gravity directs polarity of development and induces a directional, trans-cellular calcium (Ca(2+)) current. To clarify how gravity polarizes this electrophysiological process, we measured the kinetics of the cellular response to changes in the gravity vector, which we initially estimated using the self-referencing calcium microsensor. In order to generate more precise and detailed data, we developed a silicon microfabricated sensor array which facilitated a lab-on-a-chip approach to simultaneously measure calcium currents from multiple cells in real time. These experiments revealed that the direction of the gravity-dependent polar calcium current is reversed in less than 25 s when the cells are inverted, and that changes in the magnitude of the calcium current parallel rapidly changing g-forces during parabolic flight on the NASA C-9 aircraft. The data also revealed a hysteresis in the response of cells in the transition from 2g to micro-g in comparison to cells in the micro-g to 2-g transition, a result consistent with a role for mechanosensitive ion channels in the gravity response. The calcium current is suppressed by either nifedipine (calcium-channel blocker) or eosin yellow (plasma membrane calcium pump inhibitor). Nifedipine disrupts gravity-directed cell polarity, but not spore germination. These results indicate that gravity perception in single plant cells may be mediated by mechanosensitive calcium channels, an idea consistent with some previously proposed models of plant gravity perception.
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Planta, 2010
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Journal of Materials Chemistry, 2011
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Habitation, 2006
Abstract: Control of oxygen and water in the root zone is vital to support plant growth in the mi... more Abstract: Control of oxygen and water in the root zone is vital to support plant growth in the microgravity environment. The ability to control these sometimes opposing parameters in the root zone is dependent upon the availability of sensors to detect these components and ...
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Environmental Science & Technology, 2008
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Biomedical Microdevices, 2009
Advancements in microfabrication technology have lead to the development of planar micro-pore ele... more Advancements in microfabrication technology have lead to the development of planar micro-pore electroporation technology. This technology has been shown to provide greater control in single cell manipulation, and electroporation which is independent from cell size. In this work we report direct and spatially resolved characterization of electric currents within a planar micropore electroporation biochip to better understand this phenomenon at the cellular level. This work was performed using a two-dimensional (2-D) vibrating probe (VP). Analysis of the spatial patterns of current density yielded a 4th order polynomial profile in the planes parallel to the biochip's surface and a three parameter hyperbolic decay profile in the planes perpendicular to the chip surface. A finite element model was developed which correlates with actual measurements on the micropore. Preliminary VP current density measurements of electroporated HepG2 cells revealed a significantly high current density minutes after electroporation even with non-electroporative pulses. These results indicate that cells take a considerable amount of time for complete electrophysiological recovery and indicate the use of the VP as a cell viability indicator for optimized electroporation.
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The objective of this work is to develop a new microsensor system that can monitor dissolved oxyg... more The objective of this work is to develop a new microsensor system that can monitor dissolved oxygen and hydration environment at the plant root zone. A miniaturized plant growth system is prepared including the root zone layer, either a porous ceramic tube or porous ceramic wafer on which the plant is grown, and an underlying fluidic channel to deliver nutrients
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The vector of gravity sets the direction of polarized development of single spore cells of the fe... more The vector of gravity sets the direction of polarized development of single spore cells of the fern Ceratopteris richardii after light initiates their germination. Gravity also sets the direction of a trans-cell calcium current, which enters the cell along its bottom and exits it from its top. The direction of this current predicts the subsequent direction of spore development, and
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Papers by Marshal Porterfield