Sodium-independent in vitro induction of Na+,K+-ATPase by aldosterone in renal target cells: permissive effect of triiodothyronine.

Abstract

The aim of this study was to develop an in vitro system in which we could study the causal relationship between short-term stimulation of Na' ,K+-ATPase in the collecting tubule by aldosterone on the one hand and protein synthesis and changes in intracellular Na+ concentration on the other hand. Previous in vivo studies suggested that triiodothyronine might facilitate aldosterone-induced stimulation of Na +,K + -ATPase. Results show that when segments of cortical collecting tubules microdissected from collagenase-treated kidneys of adrenalectomized rats were incubated for 3 hr in the presence of either 10-8 M aldosterone or 10'8 M triiodothyronine alone Na + ,K + -ATPase activity was not altered, whereas the addition of both hormones markedly stimulated the activity and the number of catalytic sites of Na+,K+-ATPase. This stimulation was abolished by actinomycin D and cycloheximide, whereas it was not altered in the absence of extraceliular sodium or in the presence of the luminal Na+-channel blocker amiloride. Thus, triiodothyronine facilitates the in vitro induction of Na+,K+-ATPase synthesis by aldosterone. Aldosterone action on Na+,K+-ATPase is independent of Na+ availability.The collecting tubule of the mammalian nephron is a major site of action of aldosterone, which stimulates Na+ reabsorption. In these cells, Na+ reabsorption from the luminal fluid to the peritubular medium is accomplished through a passive luminal entry by means of amiloride-sensitive channels and an active basolateral extrusion catalyzed by Na+,K+-ATPase. In vivo studies indicate that Na+ channels and also Na+,K+-ATPase are stimulated by aldosterone. Indeed, it has been reported previously that in vivo injection of aldosterone to adrenalectomized rats or rabbits stimulates Na+,K+-ATPase activity in the collecting tubule (1-3). However, we had been unable to reproduce this effect in vitro. Similarly, pieces of evidence for the in vitro effect of aldosterone on Na+ transport by the isolated microperfused collecting tubule in mammals are sparse and contradictory (4)(5)(6), in contrast to what is observed in vivo after administration of mineralocorticoids (5,(7)(8)(9). Because we recently demonstrated that triiodothyronine (T3) potentiates in vivo aldosterone action on the collecting tubule (10), we evaluated whether T3 might be the missing factor in in vitro induction of Na+ ,K +-ATPase by aldosterone. Indeed, incubation of single microdissected rat cortical collecting tubules (CCT) with both aldosterone and T3 markedly stimulated Na' ,K+-ATPase activity within 1-3 hr.The development of this in vitro system allowed us to further study the mechanisms underlying the stimulation of Na+,K+-ATPase by aldosterone in the rat collecting tubule. In particular, we investigated whether this stimulation is a primary action of aldosterone or whether it is secondary to the increment of intracellular Na+ concentration brought about by the rise of luminal Na+ permeability (11,12). For this purpose, we evaluated the actions of protein synthesis in...

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

“…The absence of stimulation of Na+/ K+ ATPase activity in the present studies differs from previous results in the mammalian collecting duct. A three-to sixfold increase in enzyme activity has been demonstrated in isolated CCD segments of both the rat and the rabbit in response to aldosterone (36)(37)(38)(39)(40). Two-to threefold increases in Na+/K' ATPase activity have also been demonstrated in primary cultures of rabbit CCD in response to both dexamethasone and aldosterone (41).…”

Regulation of the Na, K‐ATPase activity of Madin‐Darby Canine Kidney cells in defined medium by Prostaglandin E1 and 8‐bromocyclic AMP

“…Both aldosterone and T, have been observed to stimulate the activity of the Na*,K'-ATPase in the collecting tubule of the mammalian nephron (Barlet-Bas et al, 1988;Gick et al, 1988). Following the binding of these hormones t o high affinity receptors, the hormone-receptor complex enters the nucleus, binding to regulatory elements on DNA, and increasing the rate of transcription of the Na+,K+-ATPase genes (Lingrel et al, 1990).…”

Insulin-induced Stimulation of Na+,K+-ATPase Activity in Kidney Proximal Tubule Cells Depends on Phosphorylation of the α-Subunit at Tyr-10

“…Besides long-term regulation by steroid and thyroid hormones (Doucet et al, 1986;Barlet-Bas et al, 1987;Palmer et al, 1993), kidney tubule Na ϩ ,K ϩ -ATPase activity can be rapidly modulated through changes in cell surface expression (Beron et al, 1997;Carranza et al, 1998) and/or by modifications of the function of single-pump units (Féraille et al, 1994(Féraille et al, , 1995. In this regard, it has been demonstrated that the ␣-subunit of Na ϩ ,K ϩ -ATPase can be phosphorylated by PKA and PKC in vitro (Bertorello et al, 1991;Chibalin et al, 1992;Feschenko and Sweadner, 1995) and in intact cells (Middleton et al, 1993;Béguin et al, 1994;Féraille et al, 1995;Fisone et al, 1995;Carranza et al, 1996b).…”