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The Unique Mitochondrial Form and Function of Antarctic Channichthyid Icefishes

TitleThe Unique Mitochondrial Form and Function of Antarctic Channichthyid Icefishes
Publication TypeJournal Article
Year of Publication2010
AuthorsO’Brien, KM, Mueller, IA
JournalIntegrative and Comparative Biology
VolumeAdvance Access

Antarctic icefishes of the family Channichthyidae are the only vertebrate animals that as adults do not expressthe circulating oxygen-binding protein hemoglobin (Hb). Six of the 16 family members also lack the intracellularoxygen-binding protein myoglobin (Mb) in the ventricle of their hearts and all lack Mb in oxidative skeletal muscle.The loss of Hb has led to substantial remodeling in the cardiovascular system of icefishes to facilitate adequate oxygenationof tissues. One of the more curious adaptations to the loss of Hb and Mb is an increase in mitochondrial density incardiac myocytes and oxidative skeletal muscle fibers. The proliferation of mitochondria in the aerobic musculature oficefishes does not arise through a canonical pathway of mitochondrial biogenesis. Rather, the biosynthesis of mitochondrialphospholipids is up-regulated independently of the synthesis of proteins and mitochondrial DNA, andnewly-synthesized phospholipids are targeted primarily to the outer-mitochondrial membrane. Consequently, icefishmitochondria have a higher lipid-to-protein ratio compared to those from red-blooded species. Elevated levels ofnitric oxide in the blood plasma of icefishes, compared to red-blooded notothenioids, may mediate alterations inmitochondrial density and architecture. Modifications in mitochondrial structure minimally impact state III respirationrates but may significantly enhance intracellular diffusion of oxygen. The rate of oxygen diffusion is greater within thehydrocarbon core of membrane lipids compared to the aqueous cytosol and impeded only by proteins within the lipidbilayer. Thus, the proliferation of icefish’s mitochondrial membranes provides an optimal conduit for the intracellulardiffusion of oxygen and compensates for the loss of Hb and Mb. Currently little is known about how mitochondrialphospholipid synthesis is regulated and integrated into mitochondrial biogenesis. The unique architecture of the oxidativemuscle cells of icefishes highlights the need for further studies in this area.

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