title: Electroneutral Na+/H+ exchange in brush-border membrane vesicles from Penaeus japonicus hepatopancreas.
abstract: An electroneutral Na+/H+ exchange mechanism (dimethylamiloride inhibitable, Li+ sensitive, and Ca2+ insensitive) was identified in brush-border membrane vesicles (BBMV) from Kuruma prawn hepatopancreas by monitoring Na(+)-dependent H+ fluxes with the pH-sensitive dye acridine orange and measuring 22Na+ uptake. Kinetic parameters measured under short-circuited conditions were the Na+ concentration that yielded one-half of the maximal dissipation rate (Fmax) of the preset transmembrane delta pH (KNa) = 15 +/- 2 mM and Fmax = 3,626 +/- 197 delta F.min-1.mg protein-1, with a Hill coefficient for Na+ of approximately 1. In addition, the inhibitory constant for dimethylamiloride was found to be approximately 1 microM. The electroneutral nature of the antiporter was assessed in that an inside-negative transmembrane electrical potential neither affected kinetic parameters nor stimulated pH-dependent (intracellular pH > extracellular pH) 22Na+ uptake. In contrast, electrogenic pH-dependent 22Na+ uptake was observed in lobster hepatopancreatic BBMV. Substitution of chloride with gluconate resulted in increasing KNa and decreasing delta Fmax, which suggests a possible role of chloride in the operational mechanism of the antiporter. These results indicate that a Na+/H+ exchanger, resembling the electroneutral Na+/H+ antiporter model, is present in hepatopancreatic BBMV from the Kuruma prawn Penaeus japonicus.
authors.affiliation: Dipartimento di Biologia, Università di Lecce, Strada Provinciale Lecce-Monteroni, Italy.
authors.forename: S
authors.initials: S
authors.lastname: Vilella
authors.forename: V
authors.initials: V
authors.lastname: Zonno
authors.forename: L
authors.initials: L
authors.lastname: Ingrosso
authors.forename: T
authors.initials: T
authors.lastname: Verri
authors.forename: C
authors.initials: C
authors.lastname: Storelli
mesh_terms: D000584:Amiloride / Q000031:analogs & derivatives / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000494:pharmacology; D002712:Chlorides / Q000494:pharmacology; D004064:Digestive System / Q000648:ultrastructure*; D004563:Electrochemistry; D006859:Hydrogen / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008094:Lithium / Q000494:pharmacology; D008871:Microvilli / Q000378:metabolism*; D033561:Penaeidae / Q000378:metabolism*; D012964:Sodium / Q000378:metabolism / Q000494:pharmacology; D017923:Sodium-Hydrogen Exchangers / Q000187:drug effects / Q000378:metabolism*
chemical_list: D002712:Chlorides; D017923:Sodium-Hydrogen Exchangers; C039465:5-dimethylamiloride; D000584:Amiloride; D006859:Hydrogen; D008094:Lithium; D012964:Sodium; D002118:Calcium