Meeting Abstract

60.10  Tuesday, Jan. 6  The influence of oxygen and high-energy phosphate diffusion on metabolic scaling in three species of tail-flipping crustaceans. JIMENEZ, A.G.; LOCKE, B.R.; KINSEY, S.T.*; University of North Carolina Wilmington kinseys@uncw.edu

We examined the influence of intracellular diffusion of O₂ and high-energy phosphate (HEP) molecules on the scaling with body mass of the post-exercise whole animal rate of O₂ consumption (VO₂) and muscle arginine phosphate (AP) re-synthesis rate, as well as muscle citrate synthase (CS) activity in 3 groups of tail-flipping crustaceans. Two size classes in each of three taxa (Palaemonetes pugio, Penaeus spp. and Panulirus argus) were examined that together encompassed a 27,000-fold range in mean body mass. In all species, muscle fiber size increased with body mass and ranged in diameter from 70 1.5 to 210 8.8 m. Thus, intracellular diffusive path lengths for O₂ and HEP molecules were greater in larger animals. The body mass scaling exponent, b, for post-tail flipping VO₂ (b=-0.21) was not similar to that for the initial rate of AP re-synthesis (b=-0.12), which in turn was different from that of CS activity (b=0.09). We developed a mathematical reaction-diffusion model that allowed an examination of the influence of O₂ and HEP diffusion on the observed rate of aerobic flux in muscle. These analyses revealed that diffusion limitation was minimal under most conditions, suggesting that diffusion may act on the evolution of fiber design, but usually does not directly limit aerobic flux. However, both within and between species, fibers were more diffusion limited as they grew larger, particularly when hemolymph PO₂ was low, which may explain some of the divergence in the scaling exponents of muscle aerobic capacity and muscle aerobic flux.