海水適應過程?郭魚(Oreochromis mossambicus)腦及鰓鈉幫浦之表現及活化

Abstract

本研究的目的為探討Na+-K+-ATPase α isoforms在廣鹽性吳郭魚(Oreochromis mossambicus）適應海水過程中表現與活化的情形。在吳郭魚自淡水轉移到25?的海水過程中，我們測定血漿滲透壓、腦及鰓上Na+-K+-ATPase的活性及蛋白質量變化。結果顯示血漿滲透壓在吳郭魚轉移後3個小時開始升高，48小時後開始下降，168小時後血漿滲透壓值回復與淡水控制組相同。鰓上Na+-K+-ATPase活性在轉移海水後1-6個小時比淡水組增加約1.7倍，而腦中Na+-K+-ATPase活性在轉移後1-6個小時比淡水組增加約6.5倍。因此由腦中活性明顯的變化，顯示魚類中樞神經系統可能對血漿滲透壓值的變化非常敏感。由西方墨點法的實驗中，我們發現吳郭魚鰓上有Na+-K+-ATPase α1和α3兩種isoform表現，腦中只有Na+-K+-ATPase α3 isoform能被偵測到。鰓上Na+-K+-ATPase α1和α3 isoform的蛋白質量及腦上α3 isoform的蛋白質量在吳郭魚適應海水過程中皆有增加的情形，然而吳郭魚鰓及腦中Na+-K+-ATPase活性在蛋白質量增加前即有活化的情形，顯示此種短期調控Na+-K+-ATPase活性上升的機制可能與Na+-K+-ATPase post-translational的調節有關。

The purpose of the present study is to examine the expression and activation of Na+-K+-ATPase α isoforms in tilapia (Oreochromis mossambicus) during seawater (SW) adaptation. Plasma osmolarity and enzyme activity and protein expression of Na+-K+-ATPase in gills and brain were measured in tilapia transferred from freshwater (FW) to 25? SW. The results showed that plasma osmolarity increased 3 hr after transfer, then started to decrease at 48 hr, and recovered to the same level as the FW control at 168 hr after transfer. Na+-K+-ATPase activities increased about 1.7 folds in gills and 6.5 folds in brain during the first 6 hr. The remarkable activation of Na pump in tilapia brain during SW adaptation indicates that the central nervous system may be extremely sensitive to plasma osmolarity disturbance. In the western blot experimemt. both of the two isoforms,α1 and α3, were expressed in tilapia gills, but only α3 isoform could be detected in brain tissue of tilapia. The expression of the two isoforms was enhanced in both gills and brain during SW adaptation. However, activities of Na pump in both gills and brain were upregulated before protein changes in the tissues, indicating that post-translational regulations of Na+-K+-ATPase may be involved in the short-term regulation of Na pump activity.