Meeting Abstract

S7.8  Tuesday, Jan. 5  Pumping without iron: The unique architecture of cardiomyocytes in the hemoglobinless Channichthyids O’BRIEN, Kristin M.*; MUELLER, Irina; Univ of Alaska, Fairbanks; Univ of Alaska, Fairbanks kmobrien@alaska.edu

The lack of hemoglobin (Hb) expression in the Family Channichthyidae is perhaps one of the most striking physiological features amongst Antarctic fishes. Since their discovery more then 50 years ago, physiologists have identified many modifications in the cardiovascular system of icefishes to compensate for the loss of Hb and in some species, myoglobin (Mb) in the heart ventricle. One alteration correlated with the loss of Hb and Mb is an increase in mitochondrial volume density in cardiomyocytes. Mitochondria occupy a stunning 36% of cell volume in hearts of species lacking Hb and Mb. In addition, the loss of Hb and Mb is correlated with substantial changes in mitochondrial architecture. We have sought to determine the molecular basis of differences in mitochondrial structure between red- and white-blooded notothenioids and to determine if differences in mitochondrial structure impact function. We have determined that the high density of mitochondria in icefish hearts does not arise through a canonical mitochondrial biogenic pathway, but rather through an increase in the size of individual mitochondria via the proliferation of outer mitochondrial membranes. An analysis of the mitochondrial proteome of red- and white-blooded notothenioids revealed a significant difference in the expression of 28 unique proteins, some of which are known to regulate mitochondrial morphology. Functional studies of isolated mitochondria have shown that state III respiration rates do not significantly differ between red- and white- blooded notothenioids. However, the rate of proton leak is lower in mitochondria from icefishes compared to red-blooded species. Current studies are aimed at understanding the potential impact of elevated temperature on mitochondrial function and thermal tolerance in Antarctic notothenioids.