title: Interactions of copper and thermal stress on mitochondrial bioenergetics in rainbow trout, Oncorhynchus mykiss.
abstract: Thermal stress may influence how organisms respond to concurrent or subsequent chemical, physical and biotic stressors. To unveil the potential mechanisms via which thermal stress modulates metals-induced bioenergetic disturbances, the interacting effects of temperature and copper (Cu) were investigated in vitro. Mitochondria isolated from rainbow trout livers were exposed to a range of Cu concentrations at three temperatures (5, 15 and 25 °C) with measurement of mitochondrial complex I (mtCI)-driven respiratory flux indices and uncoupler-stimulated respiration. Additional studies assessed effects of temperature and Cu on mtCI enzyme activity, induction of mitochondrial permeability transition pore (MPTP), swelling kinetics and mitochondrial membrane potential (MMP). Maximal and basal respiration rates, as well as the proton leak, increased with temperature with the Q10 effects being higher at lower temperatures. The effect of Cu depended on the mitochondrial functional state in that the maximal respiration was monotonically inhibited by Cu exposure while low and high Cu concentrations stimulated and inhibited the basal respiration/proton leak, respectively. Importantly, temperature exacerbated the effects of Cu by lowering the concentration of the metal required for toxicity and causing loss of thermal dependence of mitochondrial respiration. Mitochondrial complex I activity was inhibited by Cu but was not affected by incubation temperature. Compared with the calcium (Ca) positive control, Cu-imposed mitochondrial swelling exhibited variable kinetics depending on the inducing conditions, and was highly temperature-sensitive. A partial reversal of the Cu-induced swelling by cyclosporine A was observed suggesting that it is in part mediated by MPTP. Interestingly, the combination of high Cu and high temperature not only completely inhibited mitochondrial swelling but also greatly increased the respiratory control ratio (RCR) relative to the controls. Copper exposure also caused marked MMP dissipation which was reversed by N-acetyl cysteine and vitamin E suggesting a role of reactive oxygen species (ROS) in this response. Taken together, Cu impairs oxidative phosphorylation in part by inhibiting the electron transport chain (ETC), stimulating proton leak, inducing MPTP and dissipating MMP, with high temperature exacerbating these effects. Thus environmental temperature rise due to natural phenomenon or global climate change may sensitize fish to Cu toxicity by exacerbating mitochondrial dysfunction.
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: Department of Biomedical Sciences, Atlantic Veterinary College, University of Prince Edward Island, Charlottetown, PE C1A 4P3, Canada.
authors.forename: Nicole
authors.initials: N
authors.lastname: MacDonald
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: D000818:Animals; D002118:Calcium / Q000378:metabolism; D019069:Cell Respiration / Q000187:drug effects / Q000502:physiology; D003300:Copper / Q000633:toxicity*; D004734:Energy Metabolism / Q000187:drug effects* / Q000502:physiology; D006358:Hot Temperature; D008928:Mitochondria / Q000187:drug effects* / Q000502:physiology*; D033681:Mitochondrial Membrane Transport Proteins; D000083162:Mitochondrial Permeability Transition Pore; D017686:Oncorhynchus mykiss / Q000378:metabolism*; D017382:Reactive Oxygen Species; D014874:Water Pollutants, Chemical / Q000633:toxicity*
chemical_list: D033681:Mitochondrial Membrane Transport Proteins; D000083162:Mitochondrial Permeability Transition Pore; D017382:Reactive Oxygen Species; D014874:Water Pollutants, Chemical; D003300:Copper; D002118:Calcium
keywords: Copper; Membrane potential; Mitochondria; Swelling; Temperature