Jensen M K, Madsen S S, Kristiansen K
Institute of Biology, Odense University, Denmark.
J Exp Zool. 1998 Oct 15;282(3):290-300. doi: 10.1002/(sici)1097-010x(19981015)282:3<290::aid-jez2>3.0.co;2-h.
The European sea bass, Dicentrarchus labrax, tolerates salinities ranging from freshwater (FW) to hypersaline conditions. In two experiments, we analysed changes in plasma ions, muscle water content (MWC), gill Na+,K(+)-ATPase activity, and alpha-subunit mRNA expression during the course of acclimation from 15 ppt salt water to FW or high salinity seawater (HSSW). In Experiment 1, fish (6.2 +/- 1.1 g) were acclimated from 15 ppt to either FW, 5, 15, 25, 50, or 60 ppt SW and sampled after 10 days. Gill Na+,K(+)-ATPase activity was stimulated in FW- and in 50 and 60 ppt SW-groups relative to the 15 ppt control group. In Experiment 2, subgroups of fish (89 +/- 7 g) were transferred from 15 ppt SW to FW or 50 ppt SW, and sampled 1, 2, 4, and 10 days later. Plasma osmolality, [Na+] and [Cl-] decreased in the FW-group and increased in the HSSW-group one day after transfer and lasting until day 10. This was accompanied by a pronounced increase in MWC in the FW-group and an insignificant decrease in the HSSW-group. The plasma [Na+]:[Cl-]-ratio increased markedly in the FW-group and decreased slightly in the HSSW-group, suggesting acid-base balance disturbances after transfer. Gill Na+,K(+)-ATPase activity was unchanged in 15 ppt SW but doubled in FW- and HSSW-groups after transfer. In both groups, this was preceded by a 2- to 5-fold elevation of the gill alpha-subunit Na+,K(+)-ATPase mRNA level. Thus increased expression of alpha-subunit mRNA is part of the molecular mechanism of both FW and SW acclimation in sea bass. Gill Na+,K(+)-ATPase Na(+)-, K(+)-, and ouabain-affinity were similar in fish acclimated to FW, 15 ppt, and HSSW, suggesting that identical isoforms of the catalytic subunit of the enzyme are expressed irrespective of salinity.
欧洲海鲈（Dicentrarchus labrax）能够耐受从淡水（FW）到高盐环境的盐度范围。在两项实验中，我们分析了从15ppt盐水适应淡水（FW）或高盐度海水（HSSW）过程中血浆离子、肌肉含水量（MWC）、鳃Na⁺,K⁺-ATP酶活性以及α亚基mRNA表达的变化。在实验1中，将鱼（6.2±1.1克）从15ppt适应到FW、5、15、25、50或60ppt的海水，并在10天后取样。相对于15ppt对照组，FW组以及50和60ppt海水组的鳃Na⁺,K⁺-ATP酶活性受到刺激。在实验2中，将鱼（89±7克）的亚组从15ppt海水转移到FW或50ppt海水，并在转移后1、2、4和10天取样。转移后一天，FW组的血浆渗透压、[Na⁺]和[Cl⁻]下降，HSSW组则上升，并持续到第10天。这伴随着FW组MWC的显著增加和HSSW组的轻微下降。FW组的血浆[Na⁺]:[Cl⁻]比值显著增加，HSSW组略有下降，表明转移后酸碱平衡受到干扰。鳃Na⁺,K⁺-ATP酶活性在15ppt海水中未发生变化，但转移后在FW组和HSSW组中增加了一倍。在两组中，这之前鳃α亚基Na⁺,K⁺-ATP酶mRNA水平升高了2至5倍。因此，α亚基mRNA表达的增加是海鲈适应淡水和海水的分子机制的一部分。适应FW、15ppt和HSSW的鱼的鳃Na⁺,K⁺-ATP酶对Na⁺、K⁺和哇巴因的亲和力相似，这表明无论盐度如何，该酶催化亚基的相同同工型都会表达。
