환경스트레스에 노출된 피조개의 산화적 스트레스와 생리적 반응

Abstract

In Korea, the ark shell is cultivated commercially and regarded as one of the most commercially important bivalve for aquaculture. But, the production of this species in Korea peaked in 1998, and then yields have decreased gradually since 1998. The production is subjected to various limiting factors including mortality outbreaks. Mortality outbreaks may be the result of multiple factors, including exposure to contaminants (cadmium [Cd] and tributyltin [TBT]) and variations of abiotic environmental factors (temperature and salinity).

Cadmium (Cd) and tributyltin (TBT) are common contaminants of marine and freshwater ecosystems, and can induce the formation of reactive oxygen species (ROS). These ROS can, in turn, cause oxidative stress. In the present study, we investigated time-related effects of Cd (0.05 and 0.1 ppm) and TBT (5 and 10 ppb) treatment on antioxidant enzyme activity, i.e., the activity of superoxide dismutase (SOD) and catalase (CAT) in the gills and digestive glands of the ark shell, Scapharca broughtonii. In addition, hydrogen peroxide (H2O2) concentrations, lysozyme activity, and glutamate oxaloacetate transaminase (GOT) and glutamate pyruvate transaminase (GPT) levels were measured in the hemolymph. We found that Cd and TBT treatment significantly increased antioxidant enzyme mRNA expression and activity in the digestive glands and gills in a time-dependent manner. In response to the Cd and TBT treatments, antioxidant enzymes mRNA expression and activity increased up to day 5 in the digestive glands and then decreased by day 7. In the gills, antioxidant enzymes mRNA expression and activity increased up to day 3 and then decreased by day 5. Likewise, H2O2 concentrations significantly increased up to day 5 and then decreased by day 7. Finally, lysozyme activity decreased during the experimental period, whereas GOT and GPT levels were significantly increased in a timedependent manner. These results suggest that antioxidant enzymes play an important role in decreasing ROS levels and oxidative stress in ark shells exposed to Cd and TBT.

Changes in water temperature and salinity are responsible for a variety of physiological stress responses in aquatic organisms. Stress induced by these factors was recently associated with enhanced reactive oxygen species (ROS) generation, which caused oxidative damage. In the present study, we investigated the timerelated effects of changes in water temperature and salinity on mRNA expression and the activities of antioxidant enzymes (SOD and CAT) and lipid peroxidation (LPO) in the gills and digestive glands of the ark shell, Scapharca broughtonii. To investigate physiological responses, hydrogen peroxide (H2O2), lysozyme activity, aspartate aminotransferase (AspAT), and alanine aminotransferase (AlaAT) were measured in the hemolymph. Water temperature and salinity changes significantly increased antioxidant enzyme mRNA expression and activity in the digestive glands and gills in a time-dependent manner. H2O2 concentrations increased significantly in the high-temperature and hyposalinity treatments. LPO, AspAT and AlaAT levels also increased significantly in a time-dependent manner, while lysozyme activity decreased. These results suggest that antioxidant enzymes play important roles in reducing oxidative stress in ark shells exposed to changes in water temperature and salinity.