Elise Bardsley

University Honors with Honors in Marine Biology

Majors: Marine Biology and French

Supervisor: Stephen Kinsey, Biology and Marine Biology

Scaling of Mitochondrial Respiration with Body Mass in Fish White Muscle

I examined mitochondrial respiration in white muscle of summer flounder, Paralichthys dentatus. Fish white muscle often grows hypertrophically, which is an increase in fiber size with increases in muscle mass, and, in species that undergo a large increase in body mass, this can lead to very large fiber diameters. Large fiber size can lead to diffusion constraints of aerobic metabolic processes since aerobic metabolism relies on the diffusion of oxygen from the blood to mitochondria and ATP from mitochondria to cellular sites of utilization. Previous studies have examined diffusion limitations of aerobic processes in whole organisms and in isolated muscle. In the present study we examined respiration rates of isolated mitochondria, which removed all diffusion constraints. Mitochondrial respiration was measured in 14 samples of muscle from P. dentatus that ranged from 11.2 g to 718.5 g, to demonstrate the effect of body mass on the scaling of respiration. Mitochondria were isolated from white muscle and state 3 and state 4 rates of respiration yielded respiratory control ratios that were greater than 5, indicating that the mitochondrial preparations were well coupled. Protein content was determined for each sample in order to relate respiration rates to the amount of protein in the sample. Respiration rates were consistent with other studies using fish white muscle. As expected, in the absence of diffusion constraints, mitochondrial respiration rates were independent of body mass. Thus, aerobic metabolic capacity in P. dentatus white muscle is dictated solely by the muscle mitochondrial density, and not by qualitative differences in the mitochondria.