Identification of critical residues within the extracellular loop of the Epithelial Sodium Channel (ENaC)

Abstract

The epithelial Na+ channel (ENaC) plays a pivotal role in fluid homeostasis through its function in sodium reabsorption. Malfunction of this channel can lead to salt sensitive hypertension or hypotension. Although passage specific and constitutively active for the transport of Na+ ions, ENaC has exhibited self‐inhibition in the presence of excess Na+ as well as altered regulation from other ions such as Cl−. ENaC's structure is likely heterotrimeric and composed of α, β, and γ‐subunits, all contributing to proper function. In an effort to elucidate structural features of mouse αENaC, critical residues, E361 and K487, were identified using a functional yeast screen. Also, the effects of specific mutations within the extracellular region (K189 to A491) of mENaC were studied under various pH levels and in the presence of excess Cl−, K+ or Na+. Variations in the growth of yeast cells expressing wild‐type and mutant ENaC were correlated to changes in extracellular ion concentration. Residues involved in potential interactions with ions that contribute to ENaC regulation in yeast will be further characterized in mammalian cells. (Supported by NIH‐NIGMS R15GM086798)