Peter B Simpson

Publications (3)15.06 Total impact

• Article: Mitochondrial Ca2+ uptake and release influence metabotropic and ionotropic cytosolic Ca2+ responses in rat oligodendrocyte progenitors

  Peter B Simpson, James T Russell
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  ABSTRACT: Many physiologically important activities of oligodendrocyte progenitor cells (O-2A cells), including proliferation, migration and differentiation, are regulated by cytosolic Ca2+ signals. However, little is known concerning the mechanisms of Ca2+ signalling in this cell type. We have studied the interactions between Ca2+ entry, Ca2+ release from endoplasmic reticulum and Ca2+ regulation by mitochondria in influencing cytosolic Ca2+ responses in O-2A cells.Methacholine (MCh; 100 μM) activated Ca2+ waves that propagated from several initiation sites along O-2A processes.During a Ca2+ wave evoked by MCh, mitochondrial membrane potential was often either depolarized (21% of mitochondria) or hyperpolarized (20% of mitochondria), as measured by changes in the fluorescence of 5,5′,6,6′-tetrachloro-1,1′,3,3′-tetraethylbenzimidazole carbocyanine iodide (JC-1).Stimulation with kainate (100 μM) evoked a slowly rising, sustained cytosolic Ca2+ elevation in O-2A cells. This also, in some cases, resulted in either a depolarization (15% of mitochondria) or hyperpolarization (12% of mitochondria) of mitochondrial membrane potential.Simultaneous measurement of cytosolic (fluo-3 AM) and mitochondrial (rhod-2 AM) Ca2+ responses revealed that Ca2+ elevations in the cytosol evoked by either MCh or kainate were translated into long-lasting Ca2+ elevations in subpopulations of mitochondria. In some mitochondria, Ca2+ signals appeared to activate Ca2+ release into the cytosol.Inhibition of the mitochondrial Na+-Ca2+ exchanger by CGP-37157 (25 μM) decreased kainate Ca2+ response amplitude and increased the rate of return of the response to basal Ca2+ levels.Thus, both ionotropic and metabotropic stimulation evoke changes in mitochondrial membrane potential and Ca2+ levels in O-2A cells. Ca2+ uptake into some mitochondria is activated by Ca2+ entry into cells or release from stores. Mitochondrial Ca2+ release appears to play a key role in shaping kainate-evoked Ca2+ responses.
  The Journal of Physiology 04/1998; · 4.72 Impact Factor
• Article: Role of mitochondrial Ca2+ regulation in neuronal and glial cell signalling

  Peter B Simpson, James T Russell
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  ABSTRACT: It is becoming increasingly clear that mitochondrial Ca2+ uptake from and release into the cytosol has important consequences for neuronal and glial activity. Ca2+ regulates mitochondrial metabolism, and mitochondrial Ca2+ uptake and release modulate physiological and pathophysiological cytosolic responses. In glial cells, inositol 1,4,5-trisphosphate-dependent Ca2+ responses are faithfully translated into elevations in mitochondrial Ca2+ levels, which modifies cytosolic Ca2+ wave propagation and may activate mitochondrial enzymes. The location of mitochondria within neurones may partially determine their role in Ca2+ signalling. Neuronal death due to NMDA-evoked Ca2+ entry can be delayed by an inhibitor of the mitochondrial permeability transition pore, and mitochondrial dysfunction is being increasingly implicated in a number of neurodegenerative conditions. These findings are illustrative of an emerging realization by neuroscientists of the importance of mitochondrial Ca2+ regulation as a modulator of cellular energetics, endoplasmic reticulum Ca2+ release and neurotoxicity.
  Brain Research Reviews 04/1998; · 10.34 Impact Factor
• Article: Images of Ca2+ flux in astrocytes: evidence for spatially distinct sites of Ca2+ release and uptake

  Aaron D. Laskey, Bradley J. Roth, Peter B. Simpson, James T. Russell
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  ABSTRACT: In this study, we have developed a mathematical method to derive the Ca2+ fluxes underlying agonist-evoked Ca2+ waves in cultured rat cortical astrocytes. Astrocytes were stimulated with norepinephrine (100 nM) to evoke Ca2+ waves, which were recorded by measuring FIuo-3 fluorescence changes with high spatial and temporal resolution. Normalized fluorescence (ΔF/F) was analyzed in discrete cellular spaces in a series of successive slices along the length of the cell. From these data, Ca2+ flux was then calculated using a one dimensional reaction-diffusion equation which utilizes the temporal and spatial derivatives of the fluorescence data and the diffusion coefficient of Ca2+ in the cytosol. This method identified distinct sites of positive flux (Ca2+ release into the cytosol) and of negative flux (Ca2+ removal from cytosol) and showed that in astrocytes, sites of Ca2+ release from stores regularly alternate with sites of Ca2+ removal from the cytosol. Cross correlation analysis of the two distribution patterns gave positive correlation at 2 μm out of phase and a negative correlation in phase. Thapsigargin-induced Ca2+ waves were analyzed to determine if the negative flux was due to Ca2+ uptake via thapsigargin-sensitive Ca2+ pumps. Negative flux sites were still found under these conditions, suggesting that multiple mechanisms of Ca2+ removal from the cytosol may contribute to negative flux sites. This method of calculation of flux may serve as a means to describe the distribution of functional ion channels and pumps participating in cellular Ca2+ signalling.
  Cell Calcium.