title: Decreased agonist-stimulated mitochondrial ATP production caused by a pathological reduction in endoplasmic reticulum calcium content in human complex I deficiency.
abstract: Although a large number of mutations causing malfunction of complex I (NADH:ubiquinone oxidoreductase) of the OXPHOS system is now known, their cell biological consequences remain obscure. We previously showed that the bradykinin (Bk)-induced increase in mitochondrial [ATP] ([ATP](M)) is significantly reduced in primary skin fibroblasts from a patient with an isolated complex I deficiency. The present work addresses the mechanism(s) underlying this impaired response. Luminometry of fibroblasts from 6 healthy subjects and 14 genetically characterized patients expressing mitochondria targeted luciferase revealed that the Bk-induced increase in [ATP](M) was significantly, but to a variable degree, decreased in 10 patients. The same variation was observed for the increases in mitochondrial [Ca(2+)] ([Ca(2+)](M)), measured with mitochondria targeted aequorin, and cytosolic [Ca(2+)] ([Ca(2+)](C)), measured with fura-2, and for the Ca(2+) content of the endoplasmic reticulum (ER), calculated from the increase in [Ca(2+)](C) evoked by thapsigargin, an inhibitor of the ER Ca(2+) ATPase. Regression analysis revealed that the increase in [ATP](M) was directly proportional to the increases in [Ca(2+)](C) and [Ca(2+)](M) and to the ER Ca(2+) content. Our findings provide evidence that a pathological reduction in ER Ca(2+) content is the direct cause of the impaired Bk-induced increase in [ATP](M) in human complex I deficiency.
authors.affiliation: Department of Biochemistry for Molecular Life Sciences, Radboud University Nijmegen, The Netherlands.
authors.forename: Henk-Jan
authors.initials: HJ
authors.lastname: Visch
authors.forename: Werner J H
authors.initials: WJ
authors.lastname: Koopman
authors.forename: Anouk
authors.initials: A
authors.lastname: Leusink
authors.forename: Sjenet E
authors.initials: SE
authors.lastname: van Emst-de Vries
authors.forename: Lambertus W P J
authors.initials: LW
authors.lastname: van den Heuvel
authors.forename: Peter H G M
authors.initials: PH
authors.lastname: Willems
authors.forename: Jan A M
authors.initials: JA
authors.lastname: Smeitink
mesh_terms: D000255:Adenosine Triphosphate / Q000819:agonists* / Q000096:biosynthesis*; D000328:Adult; D001920:Bradykinin / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D020013:Calcium Signaling / Q000187:drug effects*; D002478:Cells, Cultured; D002648:Child; D002675:Child, Preschool; D042967:Electron Transport Complex I / Q000172:deficiency*; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D005347:Fibroblasts / Q000473:pathology; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D008928:Mitochondria / Q000378:metabolism*
chemical_list: D000255:Adenosine Triphosphate; D042967:Electron Transport Complex I; D001920:Bradykinin; D002118:Calcium