title: Bidirectional Ca2+ coupling of mitochondria with the endoplasmic reticulum and regulation of multimodal Ca2+ entries in rat brown adipocytes.
abstract: How the endoplasmic reticulum (ER) and mitochondria communicate with each other and how they regulate plasmalemmal Ca(2+) entry were studied in cultured rat brown adipocytes. Cytoplasmic Ca(2+) or Mg(2+) and mitochondrial membrane potential were measured by fluorometry. The sustained component of rises in cytoplasmic Ca(2+) concentration ([Ca(2+)](i)) produced by thapsigargin was abolished by removing extracellular Ca(2+), depressed by depleting extracellular Na(+), and enhanced by raising extracellular pH. FCCP, dinitrophenol, and rotenone caused bi- or triphasic rises in [Ca(2+)](i), in which the first phase was accompanied by mitochondrial depolarization. The FCCP-induced first phase was partially inhibited by oligomycin but not by ruthenium red, cyclosporine A, U-73122, a Ca(2+)-free EGTA solution, and an Na(+)-free solution. The FCCP-induced second phase paralleling mitochondrial repolarization was partially blocked by removing extracellular Ca(2+) and fully blocked by oligomycin but not by thapsigargin or an Na(+)-deficient solution, was accompanied by a rise in cytoplasmic Mg(2+) concentration, and was summated with a high pH-induced rise in [Ca(2+)](i), whereas the extracellular Ca(2+)-independent component was blocked by U-73122 and cyclopiazonic acid. The FCCP-induced third phase was blocked by removing Ca(2+) but not by thapsigargin, depressed by decreasing Na(+), and enhanced by raising pH. Cyclopiazonic acid-evoked rises in [Ca(2+)](i) in a Ca(2+)-free solution were depressed after FCCP actions. Thus mitochondrial uncoupling causes Ca(2+) release, activating Ca(2+) release from the ER and store-operated Ca(2+) entry, and directly elicits a novel plasmalemmal Ca(2+) entry, whereas Ca(2+) release from the ER activates Ca(2+) accumulation in, or release from, mitochondria, indicating bidirectional mitochondria-ER couplings in rat brown adipocytes.
authors.affiliation: Laboratory of Anatomy and Physiology, School of Nutritional Sciences, Nagoya Univ. of Arts and Sciences, 57 Takenoyama, Iwasaki-cho, Nissin, Aichi 470-0196, Japan. kubak@nuas.ac.jp
authors.forename: Masako
authors.initials: M
authors.lastname: Kuba
authors.forename: Yoko
authors.initials: Y
authors.lastname: Higure
authors.forename: Hisashi
authors.initials: H
authors.lastname: Susaki
authors.forename: Ryotaro
authors.initials: R
authors.lastname: Hayato
authors.forename: Kenji
authors.initials: K
authors.lastname: Kuba
mesh_terms: D052437:Adipocytes, Brown / Q000187:drug effects / Q000502:physiology*; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D020013:Calcium Signaling; D002259:Carbonyl Cyanide p-Trifluoromethoxyphenylhydrazone / Q000494:pharmacology; D002478:Cells, Cultured; D016572:Cyclosporine / Q000494:pharmacology; D004721:Endoplasmic Reticulum / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004963:Estrenes / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D007211:Indoles / Q000494:pharmacology; D007424:Intracellular Fluid / Q000378:metabolism; D008274:Magnesium / Q000378:metabolism; D053078:Membrane Potential, Mitochondrial; D008928:Mitochondria / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D009840:Oligomycins / Q000494:pharmacology; D011760:Pyrrolidinones / Q000494:pharmacology; D051381:Rats; D012402:Rotenone / Q000494:pharmacology; D012964:Sodium / Q000378:metabolism; D019284:Thapsigargin / Q000494:pharmacology; D014475:Uncoupling Agents / Q000494:pharmacology
chemical_list: D004791:Enzyme Inhibitors; D004963:Estrenes; D007211:Indoles; D009840:Oligomycins; D011760:Pyrrolidinones; D014475:Uncoupling Agents; D012402:Rotenone; C060229:1-(6-((3-methoxyestra-1,3,5(10)-trien-17-yl)amino)hexyl)-1H-pyrrole-2,5-dione; D002259:Carbonyl Cyanide p-Trifluoromethoxyphenylhydrazone; D019284:Thapsigargin; D016572:Cyclosporine; D012964:Sodium; D008274:Magnesium; D002118:Calcium; C000543:cyclopiazonic acid