In vascular endothelial cells, the mineralocorticoid hormone aldosterone increases surface abundance of the epithelial Na⁺ channel (ENaC) and stiffness of the cell cortex. The latter entails a reduced release of the vasodilator nitric oxide (endothelial dysfunction). Both aldosterone effects could be reversed or prevented by the ENaC blocker amiloride and the aldosterone antagonist spironolactone. We have recently found that it is indeed the ENaC that mediates such mechanical changes. ENaC thus presents a crucial determinant of endothelial (dys)function.

Here, we test the effect of αENaC (indispensable for ENaC function) absence on endothelial function, assessed by measures of the cortical stiffness. We employed endothelial cells of ex vivo aorta preparations from wild-type (WT) and endothelium-specific αENaC-knockout (αENaC-/-) mice. To evaluate expression of the remaining ENaC subunits, we monitored γENaC surface density.

We found that αENaC-knockout in endothelial cells led to a 36% decrease in cortical stiffness, compared to WT cells. Surface expression of γENaC remained unaffected. Application of the ENaC blocker benzamil did not reduce stiffness of αENaC-/- endothelial cells, as observed for the WT (-37%). In contrast, γENaC surface density was reduced in both cell types. ENaC blockade thus leads to channel removal from the plasma membrane, but only in the presence of αENaC is accompanied by alterations in stiffness. The aldosterone antagonist spironolactone evoked changes in cortical stiffness in αENaC-/- cells (-9%). These changes are minor compared to those measured in WT cells (-42%).

We conclude that ENaC-mediated cortical stiffening crucially relies on the expression of the α-subunit.