Aquatic Toxicology 158 (2015) 75–87 Contents lists available at ScienceDirect Aquatic Toxicology j ourna l ho me pa ge: www.elsevier.com/locate/aquatox Modulation of cadmium-induced mitochondrial dysfunction and volume changes by temperature in rainbow trout (Oncorhynchus mykiss) John O. Onukwufor a , Fred Kibenge b , Don Stevens a , Collins Kamunde a,∗ a Department of Biomedical Sciences, Atlantic Veterinary College, University of Prince Edward Island, Charlottetown, PE, Canada C1A 4P3 b Department of Pathology and Microbiology, Atlantic Veterinary College, University of Prince Edward Island, Charlottetown, PE, Canada C1A 4P3 a r t i c l e i n f o Article history: Received 22 September 2014 Received in revised form 3 November 2014 Accepted 5 November 2014 Available online 13 November 2014 Keywords: Cadmium Temperature Interactions Mitochondrial bioenergetics Mitochondrial volume Rainbow trout a b s t r a c t We investigated how temperature modulates cadmium (Cd)-induced mitochondrial bioenergetic dis- turbances, metal accumulation and volume changes in rainbow trout (Oncorhynchus mykiss). In the first set of experiments, rainbow trout liver mitochondrial function and Cd content were measured in the presence of complex I substrates, malate and glutamate, following exposure to Cd (0–100 M) at three (5, 13 and 25 ◦ C) temperatures. The second set of experiments assessed the effect of temperature on Cd- induced mitochondrial volume changes, including the underlying mechanisms, at 15 and 25 ◦ C. Although temperature stimulated both state 3 and 4 rates of respiration, the coupling efficiency was reduced at temperature extremes due to greater inhibition of state 3 at low temperature and greater stimulation of state 4 at the high temperature. Cadmium exposure reduced the stimulatory effect of temperature on state 3 respiration but increased that on state 4, consequently exacerbating mitochondrial uncoupling. The interaction of Cd and temperature yielded different responses on thermal sensitivity of state 3 and 4 respiration; the Q 10 values for state 3 respiration increased at low temperature (5–13 ◦ C) while those for state 4 increased at high temperature (13–25 ◦ C). Importantly, the mitochondria accumulated more Cd at high temperature suggesting that the observed greater impairment of oxidative phosphorylation with temperature was due, at least in part, to a higher metal burden. Cadmium-induced mitochondrial vol- ume changes were characterized by an early phase of contraction followed by swelling, with temperature changing the kinetics and intensifying the effects. Lastly, using specific modulators of mitochondrial ion channels, we demonstrated that the mitochondrial volume changes were associated with Cd uptake via the mitochondrial calcium uniporter (MCU) without significant contribution of the permeability transi- tion pore and/or potassium channels. Overall, it appears that high temperature exacerbates Cd-induced mitochondrial dysfunction and volume changes in part by increasing metal uptake through the MCU. © 2014 Elsevier B.V. All rights reserved. 1. Introduction In a natural environment aquatic ectotherms, such as fish, are particularly vulnerable to changes in temperature because their body temperatures are close to that of the environment (Stevens and Fry, 1974). Indeed, major physiological and bio- chemical processes in fish, including swimming, metabolic rate, growth and reproduction are highly affected by temperature fluc- tuations. To cope with environmental temperature change, aquatic ∗ Corresponding author at: Department of Biomedical Sciences, Atlantic Vet- erinary College, University of Prince Edward Island, 550 University Avenue, Charlottetown, PE, Canada C1A 4P3. Tel.: +1 902 566 0944; fax: +1 902 566 0832. E-mail address: ckamunde@upei.ca (C. Kamunde). organisms have evolved a wide array of mechanisms. In fish many of these mechanisms entail modulation of energy metabolism and include changes in mitochondrial membrane properties, density and enzyme activity (Guderley and St-Pierre, 2002; Kraffe et al., 2007; Lockwood and Somero, 2012; Oellermann et al., 2012). Within a zone of tolerance, these changes allow organisms to cope with the challenges associated with extreme temperatures. Because the mitochondria perform several other important func- tions such as cell signalling, redox regulation, Ca homeostasis and control of apoptosis, temperature-induced mitochondrial dysfunc- tion typically leads to loss of the cell function with cell death as the terminal sequel. Environmental temperature stress is commonly encountered together with chemical pollutants including metals such as Cd. Cad- mium is an important trace metal contaminant in aquatic systems http://dx.doi.org/10.1016/j.aquatox.2014.11.005 0166-445X/© 2014 Elsevier B.V. All rights reserved.