HARDY, KM; KINSEY, ST; Univ. of North Carolina, Wilmington ; Univ. of North Carolina, Wilmington: Effects of fiber size on post-contractile phosphagen resynthesis in crustacean muscle

ABSTRACT Fast-twitch muscle fibers of the juvenile blue crab, Callinectes sapidus, have diameters that are < 100 μm, which is typical of most cells. However, muscle fibers of the adult blue crab are extremely large and often exceed 500 μm in diameter. This exceptional increase in cell size during development would be expected to limit aerobic metabolic processes due to low cell surface area:volume (SAV) and long intracellular diffusional distances. Among the aerobic processes that might be compromised is post-contractile recovery. This may have severe functional consequences as it may limit the rate at which adult blue crabs can produce additional burst-contractions necessary for predator escape following an initial series of contractions. However, previous findings have shown increased post-contractile lactate accumulation with increasing animal size in blue crab white locomotor muscle. We hypothesized that this indicates an increasing reliance on anaerobic processes in larger animals to compensate for a deficiency in the rate of aerobic ATP synthesis during recovery. We analyzed the rate of arginine phosphate resynthesis following burst contractile activity in white muscle fibers of crabs from three size classes. There were only slight difference in the rate of recovery among white fibers, and these differences were not as extreme as expected if recovery was driven by aerobic processes alone, as determined by a reaction-diffusion mathematical analysis. It therefore appears that in order to compensate for the SAV and diffusional challenges characteristic of giant cells, blue crabs undergo a developmental shift in the metabolic processes that power recovery from exercise.