Gill Na +,K +-ATPase activity in largemouth bass ( Micropterus salmoides) from three reservoirs with different levels of mercury contamination

Abstract

Exposure to high concentrations of dissolved mercury (Hg) causes gill pathologies and interferes with ion and osmoregulation in fish. Although the gill ion-exchange enzyme Na +,K +-ATPase is inhibited by Hg in laboratory experiments, the concentrations that produce such effects are much higher than normally found in natural waters. However, Stagg et al. (1992, Mar. Environ. Res., 33: 255–266) found a significant correlation between gill Na +,K +-ATPase activity and muscle Hg concentrations in flounder ( Platicthyes flesus) collected at polluted and clean sites in estuaries, suggesting that exposure to environmentally realistic Hg levels may affect ion regulation in estuarine fish. We tested for a similar relationship in a freshwater species, largemouth bass ( Micropterus salmoides). Liver, muscle, and gill Hg concentrations differed significantly among bass from three reservoirs with similar water chemistry but different levels of Hg contamination. However, mean gill Na +,K +-ATPase activity did not vary among the reservoirs. For individual fish, gill Na +,K +-ATPase activity was not related to liver, muscle, or gill Hg concentration. Liver and muscle Hg concentrations were related to fish size, but gill Na +,K +-ATPase activity did not vary with fish size or sex. Gill Hg levels were not related to fish size. Exposure of gill homogenates to 0–10 μmol Hg 1 −1 demonstrated that Na +,K +-ATPase can be inhibited by Hg in vitro, and 50% inhibition (IC50) occurred at 0.5 μmol Hg 1 −1 Although our results support the idea that Hg can interfere with Na +,K +-ATPase activity, we were unable to detect an association between environmental exposure and gill Na +,K +-ATPase activity in wild freshwater fish.