A kinetic characterization of the gill V(H⁺)-ATPase from two hololimnetic populations of the Amazon River shrimp Macrobrachium amazonicum

This investigation examines the kinetic characteristics and effect of acclimation to a brackish medium (21 ‰S) on gill V(H⁺)-ATPase activity in two hololimnetic populations of M. amazonicum. We also investigate the cellular immunolocalization of the enzyme. Immunofluorescence findings demonstrate that the V(H⁺)-ATPase c-subunit is distributed in the apical pillar cells of shrimps in fresh water but is absent after acclimation to 21 ‰S for 10 days. V(H⁺)-ATPase activity from the Tietê River population is ≈50% greater than the Grande River population, comparable to a wild population from the Santa Elisa Reservoir, but is 2-fold less than in cultivated shrimps. V(H⁺)-ATPase activity in the Tietê and the Grande River shrimps is abolished after 21 ‰S acclimation. The apparent affinities of the V(H⁺)-ATPase for ATP (0.27 ± 0.04 and 0.16 ± 0.03 mmol L^-1, respectively) and Mg²⁺ (0.28 ± 0.05 and 0.14 ± 0.02 mmol L^-1, respectively) are similar in both populations. The absence of V(H⁺)-ATPase activity in salinity-acclimated shrimps and its apical distribution in shrimps in fresh water underpins the importance of the crustacean V(H⁺)-ATPase for ion uptake in fresh water.