Specific activity of Na−K-ATPase after adrenalectomy and hormone replacement along the rabbit nephron
- 25 Downloads
Both aldosterone and dexamethasone are known to stimulate renal Na−K-ATPase activity although their action is restricted to specific nephron segments: the collecting tubule, the target site for mineralocorticoids, and the thick ascending limb and distal convoluted tubule, the target sites for glucocorticoids. As this stimulation by corticosteroids is very fast, we attempted to establish whether it occurs through de novo synthesis of new Na−K-ATPase units or by increasing the specific activity of the Na−K-ATPase units already present.
For this purpose we studied the effects of aldosterone and dexamethasone on Na−K-ATPase specific activity in microdissected nephron segments from adrenalectomized rabbits. This specific activity was determined by the ratio of ATPase activity over the apparent number of catalytic units, as measured by specific3H ouabain binding. In the proximal tubule, neither adrenalectomy nor steroid replacement altered Na−K-ATPase activity or the apparent number of catalytic sites. In other nephron segments, adrenalectomy reduced Na−K-ATPase activity and specific3H ouabain binding concomitantly, and therefore left this enzyme's specific activity unaltered. In the cortical and outer medullary collecting tubules, 10 μg/kg aldosterone simultaneously restored both the activity and apparent number of catalytic units of Na−K-ATPase to their control levels, and therefore did not modify the specific activity of the pump. Conversely, 100 μg/kg dexamethasone increased Na−K-ATPase activity in the thick ascending limb and distal convoluted tubule without changing the apparent number of catalytic units. These results indicate that both mineraloand glucocorticoids control kidney Na−K-ATPase activity, but at different sites and by different mechanisms: Aldosterone induces appearance of new catalytic units in the collecting tubule, whereas dexamethasone increases the specific activity of pre-existing units in the thick ascending limb and distal convoluted tubule.
Key wordsAdrenalectomized rabbit Kidney microdissection Mineralocorticoid and glucocorticoid effects 3H ouabain binding
Unable to display preview. Download preview PDF.
- 1.Billaudel B, Mathias PCF, Sutter BCJ, Malaisse WJ (1984) Inhibition by corticosterone of calcium inflow and insulin release in rat pancreatic islets. J Endocrinol 100:235–244Google Scholar
- 2.Doucet A, Katz AI, Morel F (1979) Determination of Na−K-ATPase activity in single segments of the mammalian nephron. Am J Physiol 237:F105-F113Google Scholar
- 3.Dunnett CW (1955) A multiple comparison procedure for comparing several treatments with a control. J Am Stat Assn 50:1096–1121Google Scholar
- 4.El Mernissi G, Doucet A (1983) Short-term effect of aldosterone on renal sodium transport and tubular Na−K-ATPase in the rat. Pflügers Arch 399:139–146Google Scholar
- 5.El Mernissi G, Doucet A (1983) Short-term effects of aldosterone and dexamethasone on Na−K-ATPase along the rabbit nephron. Pflügers Arch 399:147–151Google Scholar
- 6.El Mernissi G, Doucet A (1984) Quantitation of3H ouabain binding and turnover of Na−K-ATPase along the rabbit nephron. Am J Physiol 247:F158-F167Google Scholar
- 7.Geering K, Girardet M, Bron C, Kraehenbuhl J-P, Rossier B (1982) Hormonal regulation of (Na+, K+)-ATPase biosynthesis in the toad bladder. Effect of aldosterone and 3,5,3′-triiodo-l-thyronine. J Biol Chem 257:10338–10343Google Scholar
- 8.Hendler ED, Torretti J, Kupor L, Epstein FH (1972) Effects of adrenalectomy and hormone replacement on Na−K-ATPase in renal tissue. Am J Physiol 222:754–760Google Scholar
- 9.Jorgensen PL (1972) The role of aldosterone in the regulation of (Na+, K+)-ATPase in rat kidney. J Steroid Biochem 3:181–191Google Scholar
- 10.Schorderet-Slatkine S, Schorderet M, Baulieu EE (1977) Inhibition of the progesterone-dependent induction of meiosis by gammexane inXenopus laevis oocytes. Biochem Biophys Res Commun 77:476–502Google Scholar