title: Combined effects of cadmium, temperature and hypoxia-reoxygenation on mitochondrial function in rainbow trout (Oncorhynchus mykiss).
abstract: Although aquatic organisms face multiple environmental stressors that may interact to alter adverse outcomes, our knowledge of stressor-stressor interaction on cellular function is limited. We investigated the combined effects of cadmium (Cd), hypoxia-reoxygenation (H-R) and temperature on mitochondrial function. Liver mitochondria from juvenile rainbow trout were exposed to Cd (0-20μM) and H-R (0 and 5min) at 5, 13 and 25°C followed by measurements of mitochondrial Cd load, volume, complex І active (A)↔deactive (D) transition, membrane potential, ROS release and ultrastructural changes. At high temperature Cd exacerbated H-R-imposed reduction of maximal complex I (CI) respiration whereas at low temperature 5 and 10μM stimulated maximal CI respiration post H-R. The basal respiration showed a biphasic response at high temperatures with low Cd concentrations reducing the stimulatory effect of H-R and high concentrations enhancing this effect. At low temperature Cd monotonically enhanced H-R-induced stimulation of basal respiration. Cd and H-R reduced both the P/O ratio and the RCR at all 3 temperatures. Temperature rise alone increased mitochondrial Cd load and toxicity, but combined H-R and temperature exposure reduced mitochondrial Cd load but surprisingly exacerbated the mitochondrial dysfunction. Mitochondrial dysfunction induced by H-R was associated with swelling of the organelle and blocking of conversion of CІ D to A form. However, low amounts of Cd protected against H-R induced swelling and prevented the inhibition of H-R-induced CI D to A transition. Both H-R and Cd dissipated mitochondrial membrane potential Δψmand damaged mitochondrial structure. We observed increased reactive oxygen species (H2O2) release that together with the protection afforded by EGTA, vitamin E and N-acetylcysteine against the Δψmdissipation suggested direct involvement of Cd and oxidative stress. Overall, our findings indicate that mitochondrial sensitivity to Cd toxicity was enhanced by the effects of H-R and temperature, and changes in mitochondrial Cd load did not always explain this effect.
authors.affiliation: Department of Biomedical Sciences, Atlantic Veterinary College, University of Prince Edward Island, Charlottetown, PE C1A 4P3, Canada.
authors.forename: John O
authors.initials: JO
authors.lastname: Onukwufor
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 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; D015415:Biomarkers / Q000378:metabolism; D002104:Cadmium / Q000633:toxicity*; D015687:Cell Hypoxia / Q000502:physiology*; D019069:Cell Respiration / Q000187:drug effects / Q000502:physiology; D005260:Female; D006358:Hot Temperature / Q000009:adverse effects*; D053078:Membrane Potential, Mitochondrial / Q000187:drug effects / Q000502:physiology; D008930:Mitochondria, Liver / Q000187:drug effects* / Q000502:physiology / Q000648:ultrastructure; D017686:Oncorhynchus mykiss / Q000502:physiology*; D018384:Oxidative Stress / Q000187:drug effects* / Q000502:physiology; D017382:Reactive Oxygen Species / Q000378:metabolism; D014874:Water Pollutants, Chemical / Q000633:toxicity*
chemical_list: D015415:Biomarkers; D017382:Reactive Oxygen Species; D014874:Water Pollutants, Chemical; D002104:Cadmium
keywords: Cadmium; Electron transport system; Fish; Hypoxia-reoxygenation; Mitochondrial bioenergetics; Reactive oxygen species; Temperature