title: Permeability transition pore regulates both mitochondrial membrane potential and agonist-evoked Ca2+ signals in oligodendrocyte progenitors.
abstract: In this study, we investigated the importance of mitochondrial permeability transition pore (PTP) in agonist-evoked cytosolic Ca2+ ([Ca2+]c) signals in oligodendrocyte progenitor cells (OP cells). We measured transmembrane potential across the mitochondrial inner membrane (delta psi m) and [Ca2+]c in the immediate vicinity simultaneously using tetramethylrhodamine ethyl ester (TMRE) and calcium green respectively. Stimulation of OP cells with methacholine evoked robust [Ca2+]c signals in approximately 80% of cells which were either oscillatory or showed a peak followed by a plateau. Elevations in [Ca2+]c induced by supramaximal concentrations of the agonist (> 200 microM) were accompanied by changes in delta psi m in 33-42% of the total mitochondria investigated. The mitochondria that responded either depolarized (26-29%), hyperpolarized (7-13%) or showed no change (58-67%). Thus, of the responsive mitochondria, most (70%) depolarized during agonist-evoked [Ca2+]c signals. Blockade of PTP with cyclosporin A (CSA) reduced the number of mitochondria that depolarized with a corresponding increase in the number that hyperpolarized. In addition, CSA or its analogue methyl valine-4- CSA (MeVal-CSA), reduced the frequency of agonist-evoked global [Ca2+]c oscillations. In resting cells, CSA (63%) and MeVal-CSA (77%) hyperpolarized a majority of the mitochondria suggesting that PTP is constitutively active and may show flickering openings. Such hyperpolarizations were not mimicked by either cyclosporine H or verapamil and were inhibited by Ru360, which blocks the mitochondrial uniporter. This observation suggested that in resting cells, Ca2+ ions might redistribute between cytosol and mitochondrial matrix through the uniporter and the PTP. Taken together, these data suggest that PTP may play an important role in regulating delta psi m and local [Ca2+]c signals during agonist stimulation in OP cells.
authors.affiliation: Section on Cell Biology and Signal Transduction, LCMN, NICHD, National Institutes of Health, Bethesda, MD, USA.
authors.forename: S S
authors.initials: SS
authors.lastname: Smaili
authors.forename: J T
authors.initials: JT
authors.lastname: Russell
mesh_terms: D000818:Animals; D002118:Calcium / Q000502:physiology*; D020013:Calcium Signaling / Q000502:physiology*; D002259:Carbonyl Cyanide p-Trifluoromethoxyphenylhydrazone / Q000494:pharmacology; D002478:Cells, Cultured; D016572:Cyclosporine / Q000494:pharmacology; D005456:Fluorescent Dyes / Q000378:metabolism; D007425:Intracellular Membranes / Q000502:physiology*; D008564:Membrane Potentials / Q000502:physiology; D016210:Methacholine Chloride / Q000494:pharmacology; D008928:Mitochondria / Q000502:physiology*; D009836:Oligodendroglia / Q000378:metabolism / Q000502:physiology; D009942:Organometallic Compounds / Q000378:metabolism; D010539:Permeability; D051381:Rats; D013234:Stem Cells / Q000378:metabolism / Q000502:physiology
chemical_list: D005456:Fluorescent Dyes; D009942:Organometallic Compounds; C110932:tetramethyl rhodamine ethyl ester; D016210:Methacholine Chloride; D002259:Carbonyl Cyanide p-Trifluoromethoxyphenylhydrazone; D016572:Cyclosporine; D002118:Calcium