Osmotic and ionic regulation, and modulation by protein kinases, FXYD2 peptide and ATP of gill (Na, K)-ATPase activity, in the swamp ghost crab Ucides cordatus (Brachyura, Ocypodidae).

We analyzed the modulation by exogenous FXYD2 peptide and by endogenous protein kinases A and C, and Ca-calmodulin-dependent kinase, of gill (Na, K)-ATPase activity in the semi-terrestrial mangrove crab Ucides cordatus after 10-days acclimation to different salinities. Osmotic and ionic regulatory ability and gill (Na, K)-ATPase activity also were evaluated. (Na, K)-ATPase activity is stimulated by exogenous pig kidney FXYD2 peptide, while phosphorylation by endogenous protein kinases A and C and Ca/calmodulin-dependent kinase inhibits activity. Stimulation by FXYD2 and inhibition by protein kinase C and Ca/calmodulin-dependent kinase are salinity-dependent. This is the first demonstration of inhibitory phosphorylation of a crustacean (Na, K)-ATPase by Ca/calmodulin-dependent kinase. At low salinities, the (Na, K)-ATPase exhibited a single, low affinity ATP-binding site that showed Michaelis-Menten behavior. Above 18‰S, a second, cooperative, high affinity ATP-binding site appeared, corresponding to 10-20% of total (Na, K)-ATPase activity. Hemolymph osmolality was strongly hyper-/hypo-regulated in crabs acclimated at 2 to 35‰S. Cl was well hyper-/hypo-regulated although Na much less so, becoming isonatremic at elevated salinity. (Na, K)-ATPase activity was greatest in isosmotic crabs (26‰S), decreasing notably at 35‰S and also diminishing progressively from 18to 2‰S. Hyper-osmoregulation in U. cordatus showed little dependence on gill (Na, K)-ATPase activity, suggesting a role for other ion transporters. These findings reveal that the salinity acclimation response in U. cordatus consists of a suite of enzymatic and osmoregulatory adjustments that maintain its osmotic homeostasis in a challenging, mangrove forest environment.