Gill Na+,K+-ATPase and osmoregulation in the estuarine crab, Chasmagnathusgranulata Dana, 1851 (Decapoda, Grapsidae)

Some kinetic properties of gill Na+, K+-ATPase of the estuarine crab, Chasm agnathus granulata, and its involvement in osmotic adaptation were analyzed . Results suggest the presence of different Na+, K+-ATPase isoforms in ante rior and posterior gills. They have different affinities for Na+, but simil ar affinity values for K+, Mg2+, ATP and similar enzymatic profiles as a fu nction of temperature of the incubation medium. Ouabain concentrations whic h inhibit 50% of enzyme activity were also similar in the two types of gill s. Enzyme activity and affinity for Na+ are higher in posterior gills than in anterior ones. Furthermore, affinities of Na+, K+-ATPase of posterior gi lls for Na+ and K+ were similar to or higher than those of gills or other s tructures involved in the osmoregulation in several euryaline decapod crust aceans. Acclimation to low salinity was related to a significant increase i n the maximum Na+, K+-ATPase activity, mainly in posterior gills. On the ot her hand, crab acclimation to high salinity induced a significant decrease in maximum enzyme activity, both in anterior and posterior gills. These res ults are in accordance to the osmoregulatory performance showed by C. granu lata in diluted media, and point out the major role of posterior gills in t he osmoregulation of this species. (C) 2001 Elsevier Science B.V. All right s reserved.