Cellular responses to steroids in the enhancement of Na+ transport by rat collecting duct cells in culture. Differences between glucocorticoid and mineralocorticoid hormones.

Abstract

It has recently been discovered that both mineralocorticoid (MC) and glucocorticoid (GC) hormones can stimulate electrogenic Na' absorption by mammalian collecting duct cells in culture. In primary cultures of rat inner medullary collecting duct (IMCD) cells, 24-h incubation with either MC or GC agonist stimulates Na+ transport approximately threefold. We have now determined that the effects were not additive, but the time courses were different. As aldosterone is known to stimulate citrate synthase, Na+/K' ATPase activity, and ouabain binding in cortical collecting duct principal cells, we determined the effects of steroids on these parameters in IMCD cells. MC and GC agonists both produced a small increase in citrate synthase activity. There was no increase in Na + / K+ ATPase activity but specific ouabain binding was increased more than twofold by either agonist. To determine the role ofapical Na+ entry in the steroid-induced effects, the Na+ channel inhibitor, benzamil, was used. Benzamil did not alter the stimulation of citrate synthase activity by either steroid. In contrast, GC stimulation of ouabain binding was prevented by benzamil, whereas MC stimulation was not. We conclude that there are differences in the way that MC and GC hormones produce an increased Na+ transport. Both appear to produce translocation (or activation) of pumps into the basolateral membrane. GC stimulation of pump translocation requires increased Na+ entry whereas MC stimulation does not. (J. Clin. Invest. 1992.

rENaC is the predominant Na+ channel in the apical membrane of the rat renal inner medullary collecting duct.

“…The major rate limiting step in overall transepithelial Na' transport by the IMCD is the entry of Na+ across the apical (luminal) membrane through a Na+ channel. Steroid hormones such as aldosterone enhance Na+ transport through this channel (1)(2)(3).…”

“…The transmonolayer Isc and transepithelial resistance measurements were made in a modified Ussing chamber as previously described (1,2,36) on the day the cells were to be used. For each isolation used for mRNA analysis, parallel cultures were made in the large and the small Millicell filters.…”

“…For each isolation used for mRNA analysis, parallel cultures were made in the large and the small Millicell filters. The large filters were used for RNA isolation and the small filters used for the electrical measurements to be sure that the values were typical of those we have previously reported (1,2,35,36 (40). Cell-attached patches were used to detect channel activity in intact cells.…”

Short Term Effect of Aldosterone on Na,K-ATPase Cell Surface Expression in Kidney Collecting Duct Cells

“…The segment-specific cells of the ASDN express a transcellular pathway for Na ϩ reabsorption that is composed of the luminal epithelial Na ϩ channel (ENaC) and the basolateral Na,KATPase (Na ϩ pump). The activity of this Na ϩ reabsorptive pathway is controlled by aldosterone mostly via the mineralocorticoid receptor and to some extent also via the glucocorticoid receptor (5)(6)(7)(8). To prevent these nuclear corticosteroid receptors from being activated by glucocorticoids, the ASDN cells express the 11␤-hydroxysteroid dehydrogenase type 2, which metabolizes glucocorticoids (9).…”

Vasopressin potentiates mineralocorticoid selectivity by stimulating 11 beta hydroxysteroid deshydrogenase in rat collecting duct.

“…Full efficiency of the urinary concentration dilution process, which is under the control of AVP, requires the concomitant action of glucocorticoids: hydroosmotic permeability of the rabbit CCD has been shown to be synergistically increased by AVP and aldosterone (5). In addition, it has been recently demonstrated that both aldosterone and glucocorticoids are effective in controlling sodium reabsorption in the collecting duct via the MR and also the GR (33,34,35).…”