Endogenous Antioxidant Response and Lipid Peroxidation Levels in Muscle Tissue of the Cownose Ray (Rhinoptera bonasus)

Oxidative stress is the result of an imbalance between reactive oxygen species (ROS) and antioxidant response within cells. ROS generation is a natural consequence of ETC activity within the mitochondria and is associated with aerobic metabolism. Oxidative stress data on elasmobranch muscle is limited, with previous studies primarily focusing on mammalian and teleost muscle. Elasmobranch skeletal muscle is generally composed of large proportions of white muscle fibers (anaerobic), low proportions of red muscle fibers (aerobic), and low proportions of pink muscle fibers (anaerobic). The cownose ray, a benthopelagic batoid species, presents an interesting model of study because it contains relatively equal proportions of red and white fibers in the wings and hyper-developed red and pink fibers in the jaw musculature. These muscle proportions provide an excellent model system to investigate the relationship between muscle function, metabolic pathway for energy production, ROS generation, and antioxidant response. The aim of this study was to quantify and compare lipid peroxidation levels (MDA) and antioxidant activities (CAT, GPx, and SOD) between the cardiac, red, white, and pink muscle fibers. Muscle tissue samples were collected from cownose rays caught within the Manatee River in Tampa Bay, Florida. The enzymatic activities of catalase (CAT), glutathione peroxidase (GPx), and superoxide dismutase (SOD) were determined via colorimetric assays. Lipid peroxidation levels were quantified indirectly by measuring MDA via colorimetric assay. For CAT and GPx, activities were significantly higher in cardiac and red muscles when compared to the white and pink muscles. However, SOD showed the inverse of these trends, with activity being significantly higher in the white and pink muscles when compared to the cardiac and red muscles. These results suggest a correlation, positive and/or negative, between aerobic capacity and antioxidant response. MDA levels did not significantly differ between the fiber types, suggesting a conserved state of redox homeostasis in the muscle tissue