KINSEY, Stephen T.; JORDAN, Amanda; PATHI, Pragyansri; LOCKE, Bruce R.; Univ. of North Carolina, Wilmington; Florida State Univ. and Florida A and M Univ.; Florida State Univ. and Florida A and M Univ.; Florida State Univ. and Florida A and M Univ.: Effects of fiber size on metabolic design in aerobic and anaerobic locomotor muscle

Post-metamorphic growth in the blue crab entails an increase in body mass that spans several orders of magnitude. The muscle fibers that power swimming in these animals grow hypertrophically, which leads to a large increase in fiber size during development. In small crabs the muscle fiber diameter is typical of most cells (<60 μm), whereas in adult animals the fibers are giant (>600 μm). Thus, as the animals grow their muscle fibers cross the cell surface area to volume ratio (SA:V) and intracellular diffusion distance threshold that is adhered to by most cells. We have found that a number of changes occur in muscle structure, metabolic organization and metabolic flux during development to compensate for the effects of increasing cell size, and the pattern of development is different in aerobic and anaerobic fibers. To further examine the effects of intracellular organization and diffusive flux we constructed a mathematical reaction-diffusion model of a contraction recovery cycle in blue crab locomotor muscle. The model results suggest that the interaction between mitochondrial ATP production rates, ATP consumption rates and diffusion distances yield a system that is almost, but not quite, limited by diffusive flux. Based on this first iteration of the model it appears that fiber SA:V exerts more control than intracellular diffusive flux over the developmental changes in metabolic organization and metabolic fluxes that characterize these muscles.