HARDY, KM**; KINSEY, ST; Univ. of North Carolina Wilmington; Univ. of North Carolina Wilmington: The Effects of Cell Size on Post-Contractile Arginine Phosphate Recovery and Glycogen Depletion in the Blue Crab, Callinectes sapidus

Anaerobic (light) muscle fibers that power swimming in the juvenile blue crab, Callinectes sapidus, exhibit cell diameters of <100μm, while fibers of the adult blue crab often exceed 500μm. The low cell surface area:volume (SAV) and long intracellular diffusion distances associated with large cells compromises aerobic metabolic processes, including post-contractile recovery. In contrast, blue crabs have evolved highly subdivided aerobic (dark) fibers from giant anaerobic fiber precursors, thus enabling them to maintain small functional metabolic units throughout development. Past studies showed an increasing reliance on anaerobic processes following contraction in adult blue crab muscle, which accelerates certain phases of recovery that would otherwise be limited by large cell size. We hypothesized that dark fibers, unlike light fibers, do not recruit anaerobic glycogenolysis to speed up recovery because intracellular subdivisions alleviate SAV and diffusion limitations. We analyzed the rate of arginine phosphate resynthesis and glycogen depletion following burst contractile activity in dark muscle fibers of adult and juvenile crabs. The observed differences in the rate of arginine phosphate recovery among dark fibers were consistent with differences expected from normal metabolic scaling, as determined by a reaction-diffusion mathematical analysis. As anticipated, dark fibers from both juvenile and adult animals exhibited no post-contractile glycogen depletion, indicating that these fibers do not exploit anaerobic glycogenolysis. Thus, to compensate for challenges characteristic of giant cells, blue crab light fibers invoke anaerobic processes, while dark fibers are structurally modified to facilitate an exclusively aerobic recovery.