Effects of an abrupt salinity increment on gill Na+/K+ -ATPase activity in the freshwater shrimp, Palaemon argentinus (Crustacea: Decapoda: Caridea)

ASARO, ANTONELA; PINONI, SILVINA; BAS, CLAUDIA C.; ITUARTE, ROMINA B

BIOCELL

SAB

Lugar: Mendoza; Año: 2022 vol. 46 p. 23 - 23

The “freshwater” shrimp Palaemon (= Palaemonetes) argentinus is able to live and reproduce in fresh water, but also in salinities near sea water. This shrimp is thus a good model to assess the underlying mechanisms that allows tolerance to high salinity, which are still unknown for most aquatic taxa. In the present study, we assessed the Na+/K+-ATPase (NKA) activity in isolated gills of P. argentinus adults kept in fresh water (1‰) and suddenly transferred to concentrated salinities (15 and 25 ‰) for a short (6 h), a medium (48 h), and a long (≥ 3 weeks) period. Control group (T0) were individuals kept in 1‰ and not transferred. NKA activity was estimated as nmol Pi × min−1 × mg prot−1. We used the supernatant (10000×g, 30 s) from pooled gills homogenate (homogenization medium: 0.25 M sucrose/ 0.5 mM EGTA-Tris (pH 7.4) (4 mL buffer × g of tissue−1). Total activity was determined by measuring ATP (5 mM) hydrolysis in a reaction medium: 100 mM NaCl, 30 mM KCl, 10 mM MgCl2, 0.5 mM EGTA in 20 mM buffer imidazole (pH 7.4). Basal activity was measured in the same reaction medium, but without KCl and in presence of 1 mM ouabain. NKA activity was the difference between both assays. We analyzed the activity changes (NKA and basal) through exposure times using ANOVAs within each salinity, and HolmSidak test for a posteriori comparisons vs. T0. The activity changes for an exposure time were compared between salinities by Student’s t. Abrupt transfer of P. argentinus from 1 to 15 ‰ induced changes in NKA activity (ANOVA: F(3; 34) = 5.5; P = 0.002), causing a decrement of 35% after 48 h (T0 = 1002.85 ± 172.18 vs. 48 h = 345.54 ± 49.69; Holm-Sidak, P < 0.05). Abrupt transfer from 1 to 25 ‰ induced changes in NKA activity depending on exposure time (ANOVA: F(3; 35) = 4.802; P = 0.006), although there was no differences from T0. NKA activity at 48 h differed between salinities, it was lower at 15 than at 25 ‰ (345.54 ± 49.69 vs. 596.31 ± 77.26, respectively; t = −2.73; P = 0.015). After long exposure time to concentrated salinity, NKA activity reached values similar to those obtained at T0. Abrupt transfer of P. argentinus to concentrated salinities induced changes in basal activity between exposure times (ANOVAs 15‰: F(3; 34) = 3.69; P = 0.022; 25‰: F(3; 37) = 4.43; P = 0.01), but there was no changes compared to T0 (Holm-Sidak P > 0.05). After 6 h of exposure, the basal activity was lower in 15 than in 25 ‰ (t = −2.31; P = 0.036), suggesting that other ATPases, in addition to NKA, are involved in rapid physiological adjustments in response to sudden salinity increment.