Meeting Abstract

54.1  Jan. 6  Morphological adaptations in large muscle fibers secondarily evolved for aerobic locomotor function HARDY, KM*; KINSEY, ST; UNCW; UNCW kmh6265@uncw.edu

Swimming muscles of the blue crab, Callinectes sapidus, undergo extreme hypertrophic cell growth during post-metamorphic development, reaching dimensions that far exceed normal cells. The low cell surface area:volume and long intracellular diffusion distances associated with large cells compromise aerobic metabolism. While this does not impede contraction in the anaerobic light fibers, the rate of aerobic processes are limited. However, blue crabs have large dark fibers with a high aerobic capacity that power sustained swimming. It is likely that the dark fibers have evolved structural and physiological modifications to facilitate aerobic activity. For example, they have a network of intracellular subdivisions whose effective diameter is closer to that of a normal cell. We hypothesized that the dark fibers have metabolic functional units that are a constant size during development, but a contractile functional unit that grows hypertrophically to extreme dimensions. These fibers were expected to exhibit pronounced intrafiber perfusion to promote oxygen flux to the cell�s interior, but incomplete cytoplasmic isolation between the individual subdivisions. To explore the microvasculature, we used wheat germ agglutinin to label the endothelial cells and microbeads to fill the vessel spaces. Both techniques confirmed the presence of an elaborate network of vessels in the dark fibers compared to the light fibers. To ascertain the degree of cytoplasmic connectedness between subdivisions we used fluorescence recovery after photobleaching to compare diffusion coefficients (D) between fibers types. As anticipated, there was a lower D in the dark fibers, owing to the ability of the subdivision walls to stop molecular diffusion. These unique modifications allow the dark fibers to retain aerobic activity in spite of their extreme dimensions.