Meeting Abstract
Crustacean muscle fibers are some of the largest cells in the animal kingdom, with fiber diameters in the giant acorn barnacle Balanus nubilus exceeding 3 mm. Sessile animals with extreme muscle sizes and which live in the hypoxia-inducing intertidal zone – like B. nubilus – represent ideal models for probing the effects of oxygen limitation on muscle cells. We investigated changes in metabolism and structure of B. nubilus muscle in response to: normoxic immersion, anoxic immersion, or air emersion, for acute (6h) or chronic (6h exposures twice daily for 2wk) time periods. Following exposure, we immediately measured hemolymph pO2, then excised tergal depressor (TD; glycolytic) and scutal adductor (SA; oxidative) muscles to determine citrate synthase (CS) activity, lactate dehydrogenase (LDH) activity, and D-lactate. We also prepared a subset of SA and TD muscles from the chronic barnacles for histological analysis of fiber diameter (Feret’s), cross-sectional area (CSA), and myonuclear domain size. There was a decrease in hemolymph pO2 following 6h of anoxia, though not emersion, and this effect was more pronounced in the chronic than the acute experiment. Fiber CSA and diameter did not change significantly in either tissue, while myonuclear domain size in SA muscle was significantly lower in the anoxic and emersion groups than the normoxic control. Neither CS, nor LDH activity, showed any significant treatment effect in either tissue, whereas both muscles had significantly higher D-lactate levels after air emersion following acute (though not chronic) exposure. Thus far, our findings indicate that emersion is only mildly oxygen-limiting for B. nubilus, and that significant muscle plasticity is occurring during chronic emersion and anoxia.
