title: Temperature-dependence of mitochondrial function and production of reactive oxygen species in the intertidal mud clam Mya arenaria.
abstract: Mitochondrial respiration, energetic coupling to phosphorylation and the production of reactive oxygen species (ROS) were studied in mitochondria isolated from the eurythermal bivalve Mya arenaria (Myoidea) from a low-shore intertidal population of the German Wadden Sea. Measurements were conducted both within the range of the habitat temperatures (5-15 degrees C) and when subjected to heat exposure at 20 degrees C and 25 degrees C. Experimental warming resulted in an increase in the rate of state 3 and state 4 respiration in isolated mitochondria. The highest respiratory coupling ratios (RCR) were found at 15 degrees C; at higher temperatures mitochondrial coupling decreased, and release of ROS doubled between 15 and 25 degrees C. ROS production was 2-3% of total oxygen consumption in state 3 (0.3-0.5 nmol ROS mg(-1) protein min(-1)) at the habitat temperature, reaching a maximum of 4.3 % of state 3 respiration and 7 % of oligomycin-induced state 4+ respiration under heat stress. Thus, state 4 respiration, previously interpreted exclusively as a measure of proton leakage, included a significant contribution from ROS formation in this animal, especially under conditions of heat stress. Oxygen radical formation was directly dependent on temperature-controlled respiration rates in states 3 and 4 and inversely related to mitochondrial coupling (RCR+) in state 4. Mitochondrial ROS formation is therefore involved in cellular heat stress in this eurythermal marine ectotherm.
authors.affiliation: Alfred Wegener Institut for Polar and Marine Research, Columbusstrasse, 27568 Bremerhaven, Germany. abele@awi-bremerhaven.de
authors.forename: D
authors.initials: D
authors.lastname: Abele
authors.forename: K
authors.initials: K
authors.lastname: Heise
authors.forename: H O
authors.initials: HO
authors.lastname: Pörtner
authors.forename: S
authors.initials: S
authors.lastname: Puntarulo
mesh_terms: D000818:Animals; D000975:Antioxidants / Q000378:metabolism; D049872:Bivalvia / Q000166:cytology / Q000378:metabolism*; D002374:Catalase / Q000378:metabolism; D019069:Cell Respiration / Q000502:physiology; D016166:Free Radical Scavengers / Q000378:metabolism; D008315:Malondialdehyde / Q000378:metabolism; D018613:Microscopy, Confocal; D008928:Mitochondria / Q000378:metabolism*; D010084:Oxidation-Reduction; D017382:Reactive Oxygen Species / Q000378:metabolism*; D012235:Rhodamines / Q000378:metabolism; D013482:Superoxide Dismutase / Q000378:metabolism; D013696:Temperature
chemical_list: D000975:Antioxidants; D016166:Free Radical Scavengers; D017382:Reactive Oxygen Species; D012235:Rhodamines; C058319:dihydrorhodamine 123; D008315:Malondialdehyde; D002374:Catalase; D013482:Superoxide Dismutase