Porterfield D. Marshall

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Porterfield
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D. Marshall
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  • Article
    A non-invasive method for measuring preimplantation embryo physiology
    (Cambridge University Press, 2000-02) Trimarchi, James R. ; Liu, Lin ; Porterfield, D. Marshall ; Smith, Peter J. S. ; Keefe, David L.
    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 ([similar]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 [mu]m 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. Blastocysts 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.
  • Article
    Mitochondrial respiration and Ca2+ waves are linked during fertilization and meiosis completion
    (Company of Biologists Limited, 2003) Dumollard, Remi ; Hammar, Katherine M. ; Porterfield, D. Marshall ; Smith, Peter J. S. ; Cibert, Christian ; Rouviere, Christian ; Sardet, Christian
    Fertilization increases both cytosolic Ca2+ concentration and oxygen consumption in the egg but the relationship between these two phenomena remains largely obscure. We have measured mitochondrial oxygen consumption and the mitochondrial NADH concentration on single ascidian eggs and found that they increase in phase with each series of meiotic Ca2+ waves emitted by two pacemakers (PM1 and PM2). Oxygen consumption also increases in response to Ins(1,4,5)P3-induced Ca2+ transients. Using mitochondrial inhibitors we show that active mitochondria sequester cytosolic Ca2+ during sperm-triggered Ca2+ waves and that they are strictly necessary for triggering and sustaining the activity of the meiotic Ca2+ wave pacemaker PM2. Strikingly, the activity of the Ca2+ wave pacemaker PM2 can be restored or stimulated by flash photolysis of caged ATP. Taken together our observations provide the first evidence that, in addition to buffering cytosolic Ca2+, the egg's mitochondria are stimulated by Ins(1,4,5)P3-mediated Ca2+ signals. In turn, mitochondrial ATP production is required to sustain the activity of the meiotic Ca2+ wave pacemaker PM2.