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-Menten kinetics. Km values for [K(+)] (i.e., 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(+)] (i.e., 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 may contribute to improve the osmoregulatory capacity of tilapia, puffer and milkfish to acclimate in seawater and fresh water.
Lin
Chia-Hao
CH
Department of Life Sciences, National Chung-Hsing University, 250, Kuo-Kuang Road, Taichung, 402 Taiwan.
Lee
Tsung-Han
TH
D000064:Acclimatization / Q000502:physiology; D000704:Analysis of Variance; D000818:Animals; D001693:Biological Transport, Active / Q000187:drug effects; D005399:Fishes / Q000502:physiology*; D005618:Fresh Water; D005880:Gills / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D017136:Ion Transport / Q000187:drug effects; D007700:Kinetics; D011188:Potassium / Q000378:metabolism / Q000494:pharmacology*; D012623:Seawater; D012964:Sodium / Q000378:metabolism / Q000494:pharmacology*; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism*; D013045:Species Specificity
D012964:Sodium; D000254:Sodium-Potassium-Exchanging ATPase; D011188:Potassium