Human Endothelium: Target for Aldosterone

Abstract

Abstract-Aldosterone has long been known to control water and electrolyte balance by acting on mineralocorticoid receptors in kidney. However, recent studies demonstrated the presence of these receptors in nonclassical locations, including the cardiovascular system. We tested the hypothesis whether endothelial cells respond to aldosterone with changes in cell volume, a measure for ion-mediated water movement across the cell membrane. By means of atomic force microscopy in fluid, we measured volume of adherent human umbilical venous endothelial cells exposed for 72 hours to 10 nmol/L aldosterone. Over this period of time, cells swell by Ϸ18%. Aldosterone-induced swelling is prevented by 100 nmol/L of the mineralocorticoid receptor antagonist spironolactone, added to the primary endothelial cell culture. Aldosterone-treated cells dramatically shrink when 1 mol/L of the diuretic amiloride is applied. Cells deprived of aldosterone do not respond to amiloride. Our conclusions are: (1) aldosterone leads to sustained cell swelling inhibited by administration of spironolactone or the sodium channel blocker amiloride; (2) cells respond to amiloride after aldosterone exposure; (3) renal diuretics act on endothelial cells; and (4) Key Words: endothelium Ⅲ mineralocorticoids T he kidney is known to be the major target for aldosterone, a mineralocorticoid hormone synthesized in the adrenal cortex that acts on electrolyte transport in the distal nephron. 1 However, there is strong evidence that this hormone is also synthesized in heart 2 and blood vessels. 3 At these locations, it is regulated by similar mechanisms comparable to the renin-angiotensin aldosterone system. 4,5 Because of the fact that aldosterone acts on cardiomyocytes, cardiac fibroblasts, and endothelial cells, this hormone plays a major role in the development of heart failure, myocardial fibrosis, and endothelial dysfunction. 6 Moreover, there is much interest in the possibility of the use of aldosterone receptor blockade in patients to diminish pathological effects that can be produced by this hormone. 7 A study applying atomic force microscopy (AFM) on living aortic endothelial cells showed transient cell swelling that occurred over minutes and that was prevented by a high dose of amiloride known to inhibit plasma membrane Na ϩ /H ϩ exchange. 8 Although the underlying mechanism and its physiological relevance were still unclear, attention was placed on data suggesting that endothelial cells not only synthesize aldosterone 3 but also express mineralocorticoid receptors 9 and the epithelial sodium channel. 10 In a recent article, we applied cariporide, a specific Na ϩ /H ϩ exchange inhibitor, to human umbilical venous endothelial cells (HUVECs). 11 To our surprise, we found that the specific Na ϩ /H ϩ exchange inhibitor did not prevent aldosterone-induced cell swelling, whereas, in contrast, a low dose of amiloride known to block plasma membrane sodium channels was most effective. Taken together, these observations indicated that aldosterone triggers the "c...

Plasma sodium stiffens vascular endothelium and reduces nitric oxide release

“…Similar to kidney tubules, endothelia also express ENaC (8,11), and aldosterone that modulates the insertion of channels into the apical membrane of distal tubule cells is its major regulator (9). Results obtained in long-term experiments indicate that, after the exposure to aldosterone, endothelial cells swell (9), stiffen, and simulta- Fig.…”

“…The aldosterone concentration used in our culture media is in the high normal range in the normal population (26). The sodium-induced increase in cell stiffness is most likely linked to cell swelling because in aldosterone-treated endothelium amiloride reverses the increase in cell volume (9) and cell pressure (20). However, these data should be interpreted with particular care.…”

“…In these two studies, aldosterone was applied over 3 days before the acute application of amiloride, and it is known that over such a long time period endothelial cells accumulate organic material, possibly aldosterone-induced proteins, and thus swell because of increased oncotic pressure (20). Nevertheless, acute aldosterone application to endothelial cells also leads to amiloride-inhibitable cell swelling, which is most likely caused by the uptake of sodium and water (27). When endothelial cell pressure (technically indistinguishable of cell stiffness) is measured in response to the acute administration of aldosterone with the same time scale (Ϸ30 min), endothelial cells regulate their volume, while intracellular pressure increases (28).…”

“…This mineralocorticoid hormone is known to control the activity of epithelial sodium channels (ENaC) in the renal collecting duct. It also acts on ENaC in endothelia (7,8), where it may cause the cell to swell (9,10), stiffen (11,12), and alter its output of nitric oxide (13)(14)(15).…”

Effects of Aldosterone on the Vasculature

“…They also demonstrated that cultured human umbilical vein endothelial cells responded to aldosterone with sodium and water entry and swelling that was blocked by spironolactone. 21 Swollen aldosterone-treated endothelial cells shrunk when amiloride was applied at concentrations that do not inhibit the sodium-proton exchanger (NHE) or with cariporide, a selective inhibitor of NHE, indicating that a sodium channel similar to the epithelial sodium channel of the distal nephron was involved in this aldosterone effect. Amiloride hyperpolarizes the cell as a result of the blockade of sodium channels, inducing chloride and water efflux, and cell shrinking.…”