Short-term Effects of Hypertonic Shock on Na+, K+-ATPase Responses in Gills and Kidneys of the Spotted Green Pufferfish, Tetraodon nigroviridis.

Chia-Hao Lin and Tsung-Han Lee (2016) Freshwater (FW) spotted green pufferfish (Tetraodon nigroviridis) could be directly transferred to seawater (SW). This indicated that the spotted green pufferfish possesses an efficient osmoregulatory mechanism to overcome salinity challenges. Although previous studies explored osmoregulation in the spotted green pufferfish in FW and SW acclimation, to our knowledge, no study has addressed short-term time-course changes to elucidate the responsible mechanism. In the present study, spotted green pufferfish were transferred directly from FW to SW. We explored time-course changes in plasma osmolality, and Na+ and Cl- concentrations, as well as Na+, K+-ATPase (NKA) responses (activity and protein expression) in gills and kidneys in a short-term (96 h) time-course experiment using the spotted green pufferfish. Plasma osmolality and Cl- levels were upregulated within 3 h post-transfer, and were constant thereafter. Plasma Na+ concentration responded with a rapid increase 6 h post-transfer, and returned to the original level at 48 h post-transfer. Gills and kidneys are vital osmoregulatory organs, and NKA expressed in these organs provides the driving force for osmoregulation in euryhaline teleosts. Herein, both branchial and renal NKA responses were modulated soon after SW transfer. Branchial NKA responses including activity and protein abundance of α-subunit were significantly stimulated at 3 h post-transfer; thenceforth were maintained in at a steady state. In contrast, the activity and protein expression of renal NKA were downregulated at 3 and 12 h post-transfer, respectively. The physiological profiles found in this study illustrated how spotted green pufferfish cope with direct transferred from FW to SW.