Osmotic and ionic regulation, and kinetic characteristics of a posterior gill (Na+, K+)-ATPase from the blue crab Callinectes danae on acclimation to salinity challenge

Salt tolerance reflects ecophysiological adaptation, and the wide-ranging distribution of the Brachyura mirrors their ability to adjust body fluid concentrations. The gill (Na+, K+)-ATPase underpins such hyper/hypo-regulatory mechanisms. We evaluate osmotic and chloride regulation in Callinectes danae after 10 days acclimation to a wide salinity range (5-50 parts per thousand S), accompanying alterations in hemolymph osmolality and [Cl-] during hypo- (15 parts per thousand S) or hyper- (45 parts per thousand S) osmotic challenge. Further, we investigate posterior gill (Na+, K+)-ATPase kinetics, alpha-subunit immunolocalization and its mRNA and protein expression (15, 30 and 40 or 45 parts per thousand S). The crab is a moderate, asymmetrical hyper/hypo-osmoregulator but is a strong, asymmetrical hyper/hypo-chloride regulator. Hyper-regulation at low salinity is sustained by a threefold increase in (Na+, K+)-ATPase activity, a 3.5-fold increase in alpha-subunit mRNA expression and 1.6-fold increase in protein expression. alpha-Subunit signal is highest in 15 parts per thousand S-acclimated crabs, and is uniformly distributed throughout the ionocytes and pillar cells. Activity in 30- and 40% S-acclimated crabs is similar. Affinity for ATP and Na+ increases on high salinity acclimation but decreases for ouabain. K+ apparent affinity is independent of salinity, while that for Mg2+ decreases and for NH4+ increases with increasing salinity. A high-affinity ATP-binding site disappears on acclimation at any salinity. FOF1- and Na+- or K+-ATPase activities decrease with increased salinity. Hemolymph chloride hypo-regulation depends little on gill (Na+, K+)-ATPase activity. Hyper-, and hypo-osmotic and ionic regulatory capabilities in C. danae are intricate physiological processes underpinned by multifarious gill (Na+, K+)-ATPase kinetics and altered mRNA and protein expressions.

Automated summary

Salt tolerance in Brachyura is closely related to their ability to adjust body fluid concentrations, with mechanisms relying on the gill (Na+, K+)-ATPase. Callinectes danae demonstrates intricate osmotic and chloride regulation abilities under different salinity conditions, which are linked to variations in ATPase activity, protein expression, and mRNA expression.