Geering K, Girardet M, Bron C, Kraehenbühl J P, Rossier B C
J Biol Chem. 1982 Sep 10;257(17):10338-43.
Aldosterone stimulates transepithelial Na+ transport in the toad bladder, and thyroid hormone antagonizes this mineralocorticoid action. In the present study, we assessed the influence of these two hormones on the biosynthesis of (Na+,K+)ATPase, the major driving force of Na+ transport. Rates of enzyme synthesis were estimated by immunoprecipitation with monospecific alpha (96,000 daltons) and beta (60,000 daltons) subunit antibodies. After a 30-min pulse of intact tissue with [35S]methionine, the anti-alpha-serum recognized the 96,000-dalton alpha subunit and the anti-beta-serum, a 42,000-dalton protein, in total cell extracts. The biosynthesis rates of both these proteins were increased 2.8- and 2.4-fold respectively, over controls by 80 nM aldosterone after 18 h of hormone treatment. The hormonal effect was not apparent up to 3 h of incubation and was dose dependent between 0.2 and 20 nM aldosterone. The hormonal induction was antagonized by spironolactone (500-fold excess) but not by amiloride. The action of aldosterone thus seems to be a receptor-mediated process and a primary event independent of the Na+ permeability of the apical membrane. Thyroid hormone, on the other hand, had no effect on either basal or aldosterone-stimulated synthesis rates of both enzyme proteins. The results demonstrate a direct effect of aldosterone on gene expression of the (Na+,K+)-ATPase. Ultimately, this phenomenon could be linked to the late mineralocorticoid action of this hormone. On the other hand, thyroid hormone, in contrast to the situation in mammals, does not stimulate de novo enzyme synthesis in amphibia. Neither can the antimineralocorticoid action of thyroid hormone in the toad bladder be explained by an inhibition of the (Na+,K+)-ATPase synthesis.
醛固酮可刺激蟾蜍膀胱上皮细胞的跨上皮钠转运，而甲状腺激素则拮抗这种盐皮质激素的作用。在本研究中，我们评估了这两种激素对（钠，钾）-ATP酶生物合成的影响，（钠，钾）-ATP酶是钠转运的主要驱动力。通过用单特异性α（96,000道尔顿）和β（60,000道尔顿）亚基抗体进行免疫沉淀来估计酶的合成速率。在用[35S]甲硫氨酸对完整组织进行30分钟的脉冲标记后，抗α血清在总细胞提取物中识别出96,000道尔顿的α亚基，抗β血清识别出一种42,000道尔顿的蛋白质。在激素处理18小时后，80 nM醛固酮使这两种蛋白质的生物合成速率分别比对照增加了2.8倍和2.4倍。在孵育3小时之前，激素作用并不明显，并且在0.2至20 nM醛固酮之间呈剂量依赖性。螺内酯（过量500倍）可拮抗激素诱导作用，但氨氯吡咪则无此作用。因此，醛固酮的作用似乎是一个受体介导的过程，是一个独立于顶端膜钠通透性的主要事件。另一方面，甲状腺激素对两种酶蛋白的基础合成速率或醛固酮刺激的合成速率均无影响。结果表明醛固酮对（钠，钾）-ATP酶的基因表达有直接作用。最终，这种现象可能与该激素的晚期盐皮质激素作用有关。另一方面，与哺乳动物的情况相反，甲状腺激素不会刺激两栖动物从头合成酶。蟾蜍膀胱中甲状腺激素的抗盐皮质激素作用也不能通过抑制（钠，钾）-ATP酶的合成来解释。
