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COMPARATIVE AND EVOLUTIONARY PHYSIOLOGY

A skeletal muscle model of extreme hypertrophic growth reveals the influence of diffusion on cellular design

¹Department of Biology and Marine Biology, University of North Carolina Wilmington, Wilmington, North Carolina; and ²Department of Chemical and Biomedical Engineering, Florida State University, Florida A&M University-Florida State University College of Engineering, Tallahassee, Florida

Submitted 4 February 2009 ; accepted in final form 20 March 2009

Muscle fibers that power swimming in the blue crab Callinectes sapidus are <80 µm in diameter in juveniles but grow hypertrophically, exceeding 600 µm in adults. Therefore, intracellular diffusion distances become progressively greater as the animals grow and, in adults, vastly exceed those in most cells. This developmental trajectory makes C. sapidus an excellent model for characterization of the influence of diffusion on fiber structure. The anaerobic light fibers, which power burst swimming, undergo a prominent shift in organelle distribution with growth. Mitochondria, which require O₂ and rely on the transport of small, rapidly diffusing metabolites, are evenly distributed throughout the small fibers of juveniles, but in the large fibers of adults they are located almost exclusively at the fiber periphery where O₂ concentrations are high. Nuclei, which do not require O₂, but rely on the transport of large, slow-moving macromolecules, have the inverse pattern: they are distributed peripherally in small fibers but are evenly distributed across the large fibers, thereby reducing diffusion path lengths for large macromolecules. The aerobic dark fibers, which power endurance swimming, have evolved an intricate network of cytoplasmically isolated, highly perfused subdivisions that create the short diffusion distances needed to meet the high aerobic ATP turnover demands of sustained contraction. However, fiber innervation patterns are the same in the dark and light fibers. Thus the dark fibers appear to have disparate functional units for metabolism (fiber subdivision) and contraction (entire fiber). Reaction-diffusion mathematical models demonstrate that diffusion would greatly constrain the rate of metabolic processes without these developmental changes in fiber structure.

metabolism; mitochondria; nuclei; reaction-diffusion modeling; crustacean

This article has been cited by other articles:

				E. J. Eliason DIFFUSION INFLUENCES CELL DESIGN J. Exp. Biol., September 1, 2009; 212(17): iv - iv. [Full Text] [PDF]