Functional characterisation of mammalian epithelial sodium channels and the pathological consequences of sodium hyperabsorption in the airways

Epithelial sodium channels (ENAC) are hugely important in Na+ and water homeostasis, a mechanism essential for survival in a terrestrial environment. ENaCs are thought to be composed of three subunits α, β and γ subunits that are thought to form a heterotrimeric structure. This project will investigate isoforms of epithelial sodium channels that deviate from the αβγENaC composition, noncanonical ENaCs. The project will utilize Xenopus laevis oocytes and cell line models with the aim of characterising the electrophysiological and biophysical profiles as well as the subunit composition of noncanonical ENaCs. The project will explore whether ENaC subunits, α, and δ interact forming heteromeric assemblies to define a possible novel route for transmembrane Na+ transport. It has been suggested that acid-sensing ion channel (ASIC) subunits interact with ENaC forming noncanonical ENaC isoforms. To investigate these ASIC subunits will be expressed oocytes in various combinations with ENaC subunits. The goal of which is to evidence that ASIC/ENaC subunit assemblies form functional noncanonical ENaC channels. ASIC/ENaC channels will also be investigated as a potential nonselective cation channel (NSC) in airway epithelial cells. A novel library of amiloride analogues synthesised by our collaborators at KU Leuven, Belgium, will be screened for ENaC & ENaC/ASIC isoform inhibition. The pharmacological toolbox for studying specific ENaC isoforms is sparse, we aim to discover isoform-specific inhibitors by screening novel amiloride analogues which may provide information as to the relationship between channel activity and composition.