LIN, Chia-Hao; LEE, Tsung-Han; Dept. of Life Sci., Natl. Chung Hsing Univ.; Dept. of Life Sci., Natl. Chung Hsing Univ.: Sodium or potassium ions activate different kinetics of gill Na, K-ATPase in three seawater- and freshwater-acclimated euryhaline teleosts

The effects of [Na⁺] or [K⁺] on Na, K-ATPase activity of FW-acclimated and SW-acclimated tilapia, puffer and milkfish were examined in gill homogenates. [Na⁺] or [K⁺] stimulated Na, K-ATPase hydrolyzing ATP in all experimental groups. ATP hydrolysis stimulated by [Na⁺] or [K⁺] followed Michaelian kinetics. Km values for [K⁺] (Km,_K), were lower in SW- than FW-acclimated tilapia and puffer fishes (tilapia: 8.69�0.22 vs. 11.93�1.17 mM; puffer: 13.51�1.39 vs. 30.52�2.66 mM). Km values for [Na⁺] (Km,_Na), were lower in FW- than SW-acclimated milkfish (3.76�0.54 vs. 7.55�1.08 mM). These data suggest that [K⁺] stimulates ATP hydrolysis to rates higher in SW- than FW-acclimated tilapia and puffer fishes, while [Na⁺] stimulated ATP hydrolysis at rates higher in FW- than SW-acclimated milkfish. This is the first demonstration that Na, K-ATPase activity of euryhaline tilapia, puffer, and milkfish modulated by [Na⁺] or [K⁺] have different effects between FW- and SW-acclimated groups. Such responses as changes in properties of branchial Na, K-ATPase maybe contribute to improve the osmoregulatory capacity of tilapia, puffer and milkfish to acclimate in seawater and fresh water.