A radical approach to beating hypoxia: depressed free radical release from heart fibres of the hypoxia-tolerant epaulette shark (<Emphasis Type="Italic">Hemiscyllum ocellatum</Emphasis>) |
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Authors: | Email author" target="_blank">Anthony?J?R?HickeyEmail author Gillian?M?C?Renshaw Ben?Speers-Roesch Jeffrey?G?Richards Yuxiang?Wang Anthony?P?Farrell Colin?J?Brauner |
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Institution: | (1) School of Biological Sciences, The University of Auckland, Auckland, New Zealand;(2) Hypoxia and Ischemia Research Unit, School of Physiotherapy and Exercise Science, Griffith University, Brisbane, QLD, Australia;(3) Department of Zoology, University of British Columbia, Vancouver, BC, Canada;(4) Department of Biology, Queens University, Kingston, ON, Canada;(5) Faculty of Land and Food Systems, University of British Columbia, Vancouver, BC, Canada |
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Abstract: | Hypoxia and warm ischemia are primary concerns in ischemic heart disease and transplant and trauma. Hypoxia impacts tissue
ATP supply and can induce mitochondrial dysfunction that elevates reactive species release. The epaulette shark, Hemiscyllum ocellatum, is remarkably tolerant of severe hypoxia at temperatures up to 34°C, and therefore provides a valuable model to study warm
hypoxia tolerance. Mitochondrial function was tested in saponin permeabilised ventricle fibres using high-resolution respirometry
coupled with purpose-built fluorospectrometers. Ventricular mitochondrial function, stability and reactive species production
of the epaulette shark was compared with that of the hypoxia-sensitive shovelnose ray, Aptychotrema rostrata. Fibres were prepared from each species acclimated to normoxic water conditions, or following a 2 h, acute hypoxic exposure
at levels representing 40% of each species’ critical oxygen tension. Although mitochondrial respiratory fluxes for normoxia-acclimated
animals were similar for both species, reactive species production in the epaulette shark was approximately half that of the
shovelnose ray under normoxic conditions, even when normalised to tissue oxidative phosphorylation flux. The hypoxia-sensitive
shovelnose ray halved oxidative phosphorylation flux and cytochrome c oxidase flux was depressed by 34% following hypoxic stress. In contrast, oxidative phosphorylation flux of the epaulette
shark ventricular fibres isolated from acute hypoxia exposed the animals remained similar to those from normoxia-acclimated
animals. However, uncoupling of respiration revealed depressed electron transport systems in both species following hypoxia
exposure. Overall, the epaulette shark ventricular mitochondria showed greater oxidative phosphorylation stability and lower
reactive species outputs with hypoxic exposure, and this may protect cardiac bioenergetic function in hypoxic tropical waters. |
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