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The sodium, potassium adenosine triphosphatase (Na,K-ATPase) of the gill is responsible for the ability of the blue crab (Callinectes sapidus), to maintain serum osmolality in dilute environments. Thus, the inhibition of this enzyme might lead to osmoregulatory failure. To determine whether this mechanism plays a role in DDT toxicity in the blue crab, the effects of DDT on gill Na,K-ATPase activity and osmoregulation were examined in adult crabs. When DDT was presented to gill homogenates in vitro, Na,K-ATPase was significantly inhibited at a concentration of 1.0 ppm DDT. Essentially maximal inhibition occurred at 9.0 ppm. The injection of a sublethal dose of DDT (0.3 ppm) into the live animal produced a temporary decline in hemolymph osmolality. However, by 28 h after transfer of the animal to a dilute environment, the values for osmolality and Na,K-ATPase activity were virtually identical to those of controls. Since the intact animal showed only a transient osmoregulatory response to DDT, even though the Na,K-ATPase was sensitive to DDT in vitro, the authors suggest that, in vivo, either (1) rapid induction, or activation, of new Na,K-ATPase activity or (2) excess sodium transport capacity protects the crab from osmoregulatory difficulty.
Na, K-ATPase, DDT, osmoregulation, osmolality, aquatic toxicology
Intergovernmental Personnel Act fellow, Emporia State University, Emporia, Kans.
Research physiologist, Laboratory of Pharmacology, National Institute of Environmental Health Sciences, N.C.