69.4 Saturday, Jan. 5 Multiplying mitochondria in the cold: how do fish do it and why? O'BRIEN, K.M.; Univ. of Alaska Fairbanks firstname.lastname@example.org
High mitochondrial densities are characteristic of oxidative muscles in cold-bodied fishes. There is a latitudinal trend in mitochondrial abundance, with Antarctic fishes displaying the highest densities. Antarctic icefishes, lacking hemoglobin, lie at the extreme end of this continuum, with mitochondria displacing as much as 52% of the cell volume in some species. High mitochondrial densities enhance ATP production and minimize diffusion distances for oxygen and metabolites in the cold. Previous studies have shown that mitochondrial-rich muscles may be necessary for cold-adapted fishes because mitochondrial function has not completely compensated for the cold. We measured rates of respiration and proton leak in mitochondria from both red- and white-blooded Antarctic fishes and found that state III respiration rates are similar to some temperate fish, and most surprising, proton leak is markedly lower. These results suggest that high mitochondrial densities in muscles of Antarctic fishes may be more important for minimizing diffusion constraints than compensating for inefficiencies. How high mitochondrial densities arose during the evolution of Antarctic fishes, and in icefishes in particular, is largely unknown. Our studies suggest membrane proliferation played a role in icefishes, in a pathway distinct from mammalian mitochondrial biogenesis.