Figure 1.

An intracellular ENaC trafficking model. (1) An insertion state (Insert): this state contains epithelial Na⁺ channel (ENaC) that accesses to the apical membrane with an insertion rate into the apical membrane ($k_I$). (2) An apical membrane state (Apical): this state contains ENaC that functions as Na⁺-conducting (permeant) pathways across the apical membrane. (3) A recycling state (Recycl): this state contains ENaC retrieved from the apical membrane with an endocytotic rate ($k_E$), and then the ENaC is trafficked back to the insertion state (Insert) with a recycling rate ($k_R$), or moves to a degradation pathway (Degrad) with a degradation rate ($k_D$).