Expression of the epithelial Na+ channel and other components of an aldosterone response pathway in human adrenocortical cells

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Abstract

We have unexpectedly found expression of the epithelial Na+ channel (ENaC) in human adrenocortical cells and tested the hypothesis that these cells contain the components of an aldosterone response pathway. Tissue was obtained from patients undergoing adrenalectomy and mRNA and protein expression of recognised components of an aldosterone-response pathway were determined by RT-PCR and Western blotting. The effects of mineralocorticoid receptor agonists and antagonists, amiloride analogues, and extracellular Na+ on basal and stimulated aldosterone release from immortalised (H295R) cells were determined by radioimmunoassay. Expression of mRNA for α-, β- and γ-subunits of ENaC, the mineralocorticoid receptor, Nedd4L, Sgk1 and 11β hydroxysteroid dehydrogenase type II was confirmed in human adrenal cortex. Using Western blotting α-, β- and γ-ENaC expression was demonstrated in adrenocortical cells. Measurements of 24 h aldosterone release from H295R cells showed stimulation by K+ and angiotensin II, suppression by both Na+ and high-concentration 5-(N-ethyl-N-isopropyl) amiloride (EIPA, blocker of Na+–H+ exchange) and no change with benzamil (ENaC blocker). 22Na-uptake into H295R cells was inhibited by EIPA, but not by benzamil. Our experiments suggest that the components of an aldosterone response pathway are present in human adrenal cortex. Studies in H295R cells, however, suggest that ENaC is not an important mediator of 22Na-uptake or aldosterone production. Further studies are required to determine the importance of an adrenal aldosterone response pathway.

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