The amiloride-sensitive epithelial Na⁺ channel (ENaC) is usually found in the apical membrane of epithelial cells. There, the ion channel mediates sodium reabsorption in kidney, colon, lung and sweat glands. The channel is controlled by the mineralocorticoid hormone aldosterone and is involved in the regulation of the blood pressure. In epithelia ENaC function and structure are well understood. The channel consists of different subunits named a, ß, g and d and is highly conserved throughout the vertebrate order. Recent experimental data suggest that vascular endothelium expresses ENaC and thus is recognized as a novel target for aldosterone action. Therefore, we studied the expression of ENaC and its response to the mineralocorticoid hormone in several endothelial cell lines and primary cultures. With RT-PCR we identified different ENaC subunits in HUVEC, EAhy.926 and GM7373 with variable expression levels. For the determination of the total amount of ENaC in the cells Western blots were made. Apical cell surfaces were scanned by atomic force microscopy (AFM). With quantum-dot labeled antibodies we detected and quantified ENaC molecules in the plasma membrane of endothelial cells. We found that aldosterone significantly elevates the quantity of ENaC located in the plasma membrane. Using AFM we show that aldosterone exposure increases the stiffness and volume of living endothelial cells. From our results we conclude that aldosterone affects ENaC expression in endothelial cells which could be a crucial regulator of cell stiffness and thus shear stress-induced nitric oxide release.