Meeting Abstract

54.4  Jan. 6  Scaling of aerobic metabolic processes in muscle: the effect of fiber size and diffusion KINSEY, S.T.; Univ. of North Carolina Wilmington kinseys@uncw.edu

Studies of the scaling of metabolism with body mass typically focus on rates of oxygen consumption. We have investigated the scaling of an aerobic metabolic process, the rate of post-contractile phosphagen resynthesis in muscle, to determine whether aerobic capacity and aerobic metabolic function scale in parallel. We are particularly interested in the influence of intracellular metabolite diffusion on the rate of aerobic processes, and so we have examined muscle tissues from organisms that have a large developmental range in fiber size. Some crustaceans and fishes have muscle fibers that grow hypertrophically during development, leading to very large fiber diameters in adult animals, and this growth is accompanied by a shift in mitochondria toward the periphery of the fiber. Thus, the intracellular diffusion distances between mitochondrial clusters in adult animals are much greater than in juvenile animals. Using both in vivo and ex vivo muscle stimulation protocols, we have monitored phosphagen resynthesis as a function of body mass (and fiber size) and analyzed these data using reaction-diffusion mathematical models. The models allow us to examine the extent to which diffusion limits the observed rate of phosphagen resynthesis. Despite the large range in fiber size, diffusion limitation appears to be minimal in large, burst contraction fibers, and the measured aerobic process scales in parallel with aerobic capacity. However, in fibers with high rates of ATP turnover, diffusion limitation may be substantial even when diffusion distances are short, perhaps leading to divergence in the scaling of aerobic processes and aerobic capacity.