Renshaw 2015 Abstract MiP2015
|Mitochondrial responses to thermal stress: is the ability to withstand anoxia-induced stress associated with cross-tolerance to thermal stress?|
The thermal limit of cardiac mitochondrial efficiency could be a major determinant of species distribution . The effect of high temperature on brain mitochondria has been less well explored. We examined the effect of 6 temperatures (20°C, 25°C, 30°C, 37°C, 40°C and 45°C) on brain mitochondrial function in homogenates from two Orectolobiform sharks: the Epaulette shark (Hemiscyllium ocellatum), which undergoes metabolic depression in response to the stress provided by oxygen limitation (anoxia) [1,2] and the Grey carpet shark (Chilloscyllium punctatum) which does not respond to anoxia-induced stress by depressing its metabolism . Both of these sharks can occupy shallow reef flats and estuarine habitats potentially exposing them to severe temperature-induced stress during summer low tides. We measured the effect of each temperature on: i) mitochondrial coupling efficiency; ii) non-phosphorylating proton LEAK from mitochondria; and iii) changes in substrate utilisation for complex I and complex II.
High resolution oximetry with a multiple substrate-inhibitor protocol  revealed that for both species: mitochondrial coupling (efficiency) was greatest at 25°C, and maintained at 30°C but was 25% lower at 37°C and 50% lower at 40°C. Mitochondria in both species were totally uncoupled at 45°C.
Despite an exponential increased in proton LEAK as temperature increased, Epaulette mitochondria maintained their electron transport system in coupled mitochondria at 25-37°C, while Grey carpet shark mitochondria showed a 30% decrease in mitochondrial efficiency at 37°C compared to 25°C. Examination of substrate utilisation revealed that mitochondria from Epaulette shark, which undergoes metabolic depression in response to the stress of oxygen limitation (hypoxia and anoxia) had a more stable complex 1 utilisation than Grey carpet sharks, especially at 37°C. It is possible that the mitochondria from the Epaulette shark have adaptations, associated with the ability to enter a state of metabolic depression, that enable them to withstand other stressors.
• O2k-Network Lab: NZ Auckland Hickey AJ
Labels: MiParea: Respiration, Comparative MiP;environmental MiP
Stress:Oxidative stress;RONS, Temperature Organism: Fishes Tissue;cell: Nervous system Preparation: Homogenate
Coupling state: LEAK, OXPHOS, ET Pathway: N, S HRR: Oxygraph-2k Event: D1 MiP2015
1-Hypoxia Ischemia Research Unit, School Allied Health Sc, Griffith Univ, Australia; 2-School Biol Sc, Univ Auckland, New Zealand. - [email protected]
References and acknowledgements
- Iftikar FI, MacDonald J, Baker D, Renshaw GMC, Hickey AJR (2014). Are mitochondria the ultimate determinate of species distribution in a changing climate? J Exp Biol 217:2348-57.
- Renshaw GMC, Kerrisk CB, Nilsson GE (2002) The role of adenosine in the anoxic survival of the epaulette shark, Hemiscyllium ocellatum. Comp Biochem Physiol B 131:133-41.
- Chapman C, Renshaw GMC (2009) Haematological responses of the grey carpet shark (Chiloscyllium punctatum) and the Epaulette Shark (Hemiscyllium ocellatum) to Anoxia and Re-oxygenation Exposure. Exp Zool Part A 311:422-38.
- Hickey AJR, Renshaw GMC, Speers-Roesch B, Richards JG, Wang Y, Farrell AP, Brauner CJ (2012) A radical approach to beating hypoxia: depressed free radical release from heart fibres of the hypoxia-tolerant epaulette shark (Hemiscyllum ocellatum). J Comp Physiol B 182:91-100.