Vascular ENaC in human arteries and its role in hypertension

Abstract

The human epithelial sodium channel (ENaC) is a trimer composed of different combinations of 4 subunits (α, β, γ, and δ). Recent research in mice and rats has demonstrated the role of vascular αβγ-ENaC in the regulation of vascular tone and blood pressure. However, the absence of the δ subunit in these animal models makes it difficult to translate these findings into clinical settings. In this study, we aimed to characterise the expression and function of ENaC subunits in human arteries and their potential role in hypertension. Human internal mammary arteries (IMA) from patients undergoing coronary artery bypass graft (CABG) surgery were collected through the HeartOtago network. The patients were divided into three groups: normotensive, uncontrolled hypertensive, and controlled hypertensive based on their hypertensive history and blood pressure measurement before surgery. Expression of ENaC subunits was analysed by qPCR and western blot analysis. Primary endothelial cells isolated and cultured from IMA were used for the functional analysis of ENaC channels using whole-cell and single-channel patch-clamp electrophysiology. For the first time, we detected both mRNA and protein expression of all 4 ENaC subunits, both in intact IMA and in primary endothelial cells isolated from IMA. In primary endothelial cells, whole-cell patch-clamp electrophysiology revealed the presence of amiloride-sensitive current. Single-channel patch-clamp experiments identified channels with two different conductances: ~6pS (n=8) and ~12pS (n=5), that are similar to the conductance of αβγ- and δβγ-ENaC respectively. Interestingly, the δ subunit was significantly downregulated in controlled hypertensive group compared to normotensive and uncontrolled hypertensive groups at both mRNA (p>0.05) and protein levels (p>0.05). However, there was no significant change in δ-ENaC between normotensive and uncontrolled hypertensive groups. These data suggest that functional ENaC channels are expressed in IMA and δ-ENaC might have an important role in human hypertension.