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Na+, K+-ATPase Expression in Kidney of theMilkfish (Chanos chanos) Adapted to Environments of Various Salinities
虱目魚是廣鹽性海水魚類，可適應的鹽度範圍為0~158 ‰。本實驗將虱目魚飼養在高鹽海水（60 ‰）、海水（35 ‰）和淡水（0 ‰）三種鹽度環境下，並且利用組織切片和免疫化學染色，比較虱目魚長期適應（四週以上）於不同鹽度環境時，腎臟的組織型態和腎臟上Na+,K+-ATPase的分佈；並且利用real-time quantitative PCR、western blot和ATPase assay分別從mRNA含量、蛋白質含量和活性分析三種層次，探討長期適應於上述三種環境，以及轉移鹽度環境（包括由海水轉移至淡水和高鹽海水）的短期時間內，其腎臟上Na+,K+-ATPase的表現情形。由實驗結果發現，長期飼養在高鹽海水、海水及淡水的虱目魚，其腎臟所具有之各種組織構造與腎小管間NKA分佈的情況均相同；NKA活性沒有顯著差異，蛋白質含量在高鹽海水顯著高於在海水和淡水；NKA mRNA含量則是在淡水顯著高於在海水和高鹽海水。而短期適應實驗部分，NKA活性不論是轉移至淡水或高鹽海水，均無顯著變化；mRNA 和蛋白質含量，則是在轉移至淡水或高鹽海水的起初6個小時之間，有升高的現象，但接下來到第96小時之內，均回復至與轉移前相當。
此次實驗的結果顯示：(1) 虱目魚腎臟的組織結構及NKA分佈不受環境鹽度的影響；(2) NKA 的mRNA和蛋白質在虱目魚腎臟上的表現則出現不一致的變化趨勢，兩者之間似乎沒有直接的相關性。由此可知，腎臟的NKA蛋白質含量雖然受到環境鹽度變化的刺激而有變化，但是其調控作用卻非直接來自mRNA層級的影響。
Milkfish (Chanos chanos) is an euryhaline teleost which is able to survive in environment of salinities from 0‰ to 158‰. The kidney, like the gill, plays an important role in osmoregulation of euryhaline fish. The purpose of this study is to clarify the structures and localization of NKA in milkfish kidney, and to reveal renal NKA expression in milkfish adapted to water of different salinities (long-term experiment) and changes of renal NKA expression during FW- and HSW- adaptation (short-term experiment).
Juvenile milkfish (Chanos chanos) were reared in fresh water (FW, 0‰), sea water (SW, 35‰), and hypersaline water (HSW, 60‰) in the laboratory for at least three weeks. Then the long- and short-term experiment were analized. The results revealed that: (1) similar structures and NKA immunoreaction were found in kidneys of FW-, SW- and HSW-adapted milkfish; (2) in long-term adapted fish, the highest levels of NKA α-subunit protein abundance were found in the HSW group, but the highest levels of NKA mRNA abundance in the FW group, and data expressed no difference of NKA activities; (3) there was no significant difference in renal NKA activities transferred to FW and HSW. On the other hand, significant increase of NKA mRNA and α-subunit protein abundance occurred at 6 hrs after the fish were transferred from SW to FW and HSW, then decreased to the same level with the no transferred group during 96 hrs.
These results indicated that the milkfish kidney structure and renal NKA distribution were never affected by the environment salinities. On the other hand , although the amount of NKA protein were affected by the environment salinities, it was not regulated directly by the NKA mRNA.
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