Cloning and induction by low NaCl intake of avian intestine Na+ channel subunits

The alpha-subunit of the highly Na+-selective amiloride-blockable channel (ENaC) was cloned from chicken lower intestine. The deduced amino acid sequence of the avian clone exhibits similar to 60% identity to the previously cloned mammalian and amphibian alpha-subunits. It also maintains the same hydropathy profile and structural motifs. These include two transmembrane domains separated by a large extracellular loop, four extracellular N-glycosylation sites, a cysteine-rich box in the extracellular domain, and a proline-rich stretch at the carboxy terminus. Xenopus oocytes injected with cRNA transcribed from this clone express a small amiloride-blockable Na+ conductance. Degenerate primers have been used to amplify two other related products. Sequence homology indicates that one of them is the beta-subunit, whereas the other appears to represent a closely related but different transcript. Regulation of the mRNA corresponding to these clones was examined in chickens fed normal and low-NaCl rations. The low-salt diet evoked an approximately fourfold increase in the abundance of mRNA coding for the alpha-subunit, presumably through an increase in plasma aldosterone. The beta- and ''beta-like'' transcripts were even more strongly affected. The current data provide additional information on sequence conservation in the growing ENaC family and demonstrate that the avian intestine channel is strongly induced by varying NaCl intake.