title: Regulation by the exogenous polyamine spermidine of Na,K-ATPase activity from the gills of the euryhaline swimming crab Callinectes danae (Brachyura, Portunidae).
abstract: Euryhaline crustaceans rarely hyporegulates and employ the driving force of the Na,K-ATPase, located at the basal surface of the gill epithelium, to maintain their hemolymph osmolality within a range compatible with cell function during hyper-regulation. Since polyamine levels increase during the adaptation of crustaceans to hyperosmotic media, we investigate the effect of exogenous polyamines on Na,K-ATPase activity in the posterior gills of Callinectes danae, a euryhaline swimming crab. Polyamine inhibition was dependent on cation concentration, charge and size in the following order: spermine>spermidine>putrescine. Spermidine affected K(0.5) values for Na(+) with minor alterations in K(0.5) values for K(+) and NH(4)(+), causing a decrease in maximal velocities under saturating Na(+), K(+) and NH(4)(+) concentrations. Phosphorylation measurements in the presence of 20 microM ATP revealed that the Na,K-ATPase possesses a high affinity site for this substrate. In the presence of 10 mM Na(+), both spermidine and spermine inhibited formation of the phosphoenzyme; however, in the presence of 100 mM Na(+), the addition of these polyamines allowed accumulation of the phosphoenzyme. The polyamines inhibited pumping activity, both by competing with Na(+) at the Na(+)-binding site, and by inhibiting enzyme dephosphorylation. These findings suggest that polyamine-induced inhibition of Na,K-ATPase activity may be physiologically relevant during migration to fully marine environments.
authors.affiliation: Instituto de Bioquímica Médica, Laboratório de Estrutura e Regulação de Proteínas e ATPases, Programa de Biologia Estrutural, CCS, Bloco H, 2 andar, sala 26, 21941-590, RJ, Brazil.
authors.forename: E C C
authors.initials: EC
authors.lastname: Silva
authors.forename: D C
authors.initials: DC
authors.lastname: Masui
authors.forename: R P M
authors.initials: RP
authors.lastname: Furriel
authors.forename: F L M
authors.initials: FL
authors.lastname: Mantelatto
authors.forename: J C
authors.initials: JC
authors.lastname: McNamara
authors.forename: H
authors.initials: H
authors.lastname: Barrabin
authors.forename: F A
authors.initials: FA
authors.lastname: Leone
authors.forename: H M
authors.initials: HM
authors.lastname: Scofano
authors.forename: C F L
authors.initials: CF
authors.lastname: Fontes
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D003386:Brachyura / Q000033:anatomy & histology* / Q000187:drug effects*; D005618:Fresh Water; D005880:Gills / Q000187:drug effects* / Q000201:enzymology*; D006868:Hydrolysis / Q000187:drug effects; D007700:Kinetics; D009792:Oceans and Seas; D011188:Potassium / Q000494:pharmacology; D000644:Quaternary Ammonium Compounds / Q000494:pharmacology; D012964:Sodium / Q000494:pharmacology; D000254:Sodium-Potassium-Exchanging ATPase / Q000037:antagonists & inhibitors* / Q000378:metabolism*; D013095:Spermidine / Q000494:pharmacology*; D013096:Spermine / Q000494:pharmacology
chemical_list: D000644:Quaternary Ammonium Compounds; D013096:Spermine; D000255:Adenosine Triphosphate; D012964:Sodium; D000254:Sodium-Potassium-Exchanging ATPase; D011188:Potassium; D013095:Spermidine