title: Alterations in mitochondrial electron transport system activity in response to warm acclimation, hypoxia-reoxygenation and copper in rainbow trout, Oncorhynchus mykiss.
abstract: Fish expend significant amounts of energy to handle the numerous potentially stressful biotic and abiotic factors that they commonly encounter in aquatic environments. This universal requirement for energy singularizes mitochondria, the primary cellular energy transformers, as fundamental drivers of responses to environmental change. Our study probed the interacting effects of thermal stress, hypoxia-reoxygenation (HRO) and copper (Cu) exposure in rainbow trout to test the prediction that they act jointly to impair mitochondrial function. Rainbow trout were acclimated to 11 (controls) or 20°C for 2 months. Liver mitochondria were then isolated and their responses in vitro to Cu (0-20μM) without and with HRO were assessed. Sequential inhibition and activation of mitochondrial electron transport system (ETS) enzyme complexes permitted the measurement of respiratory activities supported by complex I-IV (CI-IV) in one run. The results showed that warm acclimation reduced fish and liver weights but increased mitochondrial protein indicating impairment of energy metabolism, increased synthesis of defense proteins and/or reduced liver water content. Whereas acute rise (11→20°C) in temperature increased mitochondrial oxidation rates supported by CI-IV, warm acclimation reduced the maximal (state 3) and increased the basal (state 4) respiration leading to global uncoupling of oxidative phosphorylation (OXPHOS). HRO profoundly inhibited both maximal and basal respiration rates supported by CI-IV, reduced RCR for all except CII and lowered CI:CII respiration ratio, an indication of decreased OXPHOS efficiency. The effects of Cu were less pronounced but more variable and included inhibition of CII-IV maximal respiration rates and stimulation of both CI and CIII basal respiration rates. Surprisingly, only CII and CIII indices exhibited significant 3-way interactions whereas 2-way interactions of acclimation either with Cu or HRO were portrayed mostly by CIV, and those of HRO and Cu were most common in CI and II respiratory indices. Our study suggests that warm acclimation blunts sensitivity of the ETS to temperature rise and that HRO and warm acclimation impose mitochondrial changes that sensitize the ETS to Cu. Overall, our study highlights the significance of the ETS in mitochondrial bioenergetic dysfunction caused by thermal stress, HRO and Cu exposure.
authors.affiliation: Department of Pathology and Microbiology, Atlantic Veterinary College, University of Prince Edward Island, Charlottetown, PE, C1A 4P3, Canada; Department of Biomedical Sciences, Atlantic Veterinary College, University of Prince Edward Island, Charlottetown, PE, C1A 4P3, Canada.
authors.forename: Ravinder
authors.initials: R
authors.lastname: Sappal
authors.affiliation: Faculty of Medicine, Memorial University of Newfoundland, Health Sciences Centre, Prince Philip Drive, St. John's, NL, A1B 3V6, Canada.
authors.forename: Michelle
authors.initials: M
authors.lastname: MacDougald
authors.affiliation: Department of Pathology and Microbiology, Atlantic Veterinary College, University of Prince Edward Island, Charlottetown, PE, C1A 4P3, Canada.
authors.forename: Mark
authors.initials: M
authors.lastname: Fast
authors.affiliation: Department of Biomedical Sciences, Atlantic Veterinary College, University of Prince Edward Island, Charlottetown, PE, C1A 4P3, Canada.
authors.forename: Don
authors.initials: D
authors.lastname: Stevens
authors.affiliation: Department of Pathology and Microbiology, Atlantic Veterinary College, University of Prince Edward Island, Charlottetown, PE, C1A 4P3, Canada.
authors.forename: Fred
authors.initials: F
authors.lastname: Kibenge
authors.affiliation: British Columbia Centre for Aquatic Health Sciences, 871A Island Highway, Campbell River, BC, V9W 2C2, Canada.
authors.forename: Ahmed
authors.initials: A
authors.lastname: Siah
authors.affiliation: Department of Biomedical Sciences, Atlantic Veterinary College, University of Prince Edward Island, Charlottetown, PE, C1A 4P3, Canada. Electronic address: ckamunde@upei.ca.
authors.forename: Collins
authors.initials: C
authors.lastname: Kamunde
mesh_terms: D000064:Acclimatization / Q000502:physiology*; D000818:Animals; D019069:Cell Respiration / Q000187:drug effects; D003300:Copper / Q000633:toxicity*; D004579:Electron Transport / Q000187:drug effects*; D003576:Electron Transport Complex IV / Q000378:metabolism; D004734:Energy Metabolism / Q000187:drug effects; D006358:Hot Temperature; D008928:Mitochondria / Q000187:drug effects; D008930:Mitochondria, Liver / Q000187:drug effects; D017686:Oncorhynchus mykiss / Q000378:metabolism; D010084:Oxidation-Reduction; D010085:Oxidative Phosphorylation / Q000187:drug effects; D014874:Water Pollutants, Chemical / Q000633:toxicity
chemical_list: D014874:Water Pollutants, Chemical; D003300:Copper; D003576:Electron Transport Complex IV
keywords: Copper; Electron transport system; Hypoxia-reoxygenation; Interactions; Mitochondria; Warm acclimation