Epithelial Na+ Channel (ENaC) Formed by One or Two Subunits Forms Functional Channels That Respond to Shear Force
Jan-Peter Baldin, Daniel Barth, Martin Fronius
Abstract
Canonical epithelial sodium channels (ENaCs) are heterotrimers formed by α, β and ɣ ENaC subunits in vertebrates and belong to the Degenerin/ENaC family of proteins. Proteins from this family form mechanosensitive channels throughout the animal kingdom. Activity of canonical ENaC is regulated by shear force (SF) mediating Na+ absorption in the kidney and vascular tone of arteries. Expression analysis suggests that non-canonical ENaC, formed by single or only two subunits, exist in certain tissues, but it is unknown if these channels respond to SF. α, β ɣ, and ENaC subunits were expressed either alone or in combinations of two subunits in Xenopus oocytes. Amiloride-sensitive currents and the responses to SF were assessed using two-electrode voltage clamp recordings. With the exception of ɣ ENaC all homomeric channels provided amiloride-sensitive currents and responded to SF applied via a fluid stream directed onto the oocytes. Channels containing two subunits were also activated by SF. Here the presence of the ɣ ENaC subunit when co-expressed with α or δ augmented the SF response in comparison to the αβɣ/δβɣ ENaC. Overall we provide evidence that non-canonical ENaC can from channels that respond to SF. This supports a potential function of non-canonical ENaC as mechanosensors in epithelial, vascular, and sensory cells.