CLONING AND INDUCTION BY LOW NACL INTAKE OF AVIAN INTESTINE NA+ CHANNEL SUBUNITS

The alpha-subunit of the highly Na+-selective amiloride-blockable chan nel (ENaC) was cloned from chicken lower intestine. The deduced amino acid sequence of the avian clone exhibits similar to 60% identity to t he previously cloned mammalian and amphibian alpha-subunits. It also m aintains the same hydropathy profile and structural motifs. These incl ude 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 termin us. Xenopus oocytes injected with cRNA transcribed from this clone exp ress a small amiloride-blockable Na+ conductance. Degenerate primers h ave been used to amplify two other related products. Sequence homology indicates that one of them is the beta-subunit, whereas the other app ears to represent a closely related but different transcript. Regulati on of the mRNA corresponding to these clones was examined in chickens fed normal and low-NaCl rations. The low-salt diet evoked an approxima tely fourfold increase in the abundance of mRNA coding for the alpha-s ubunit, 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 i n the growing ENaC family and demonstrate that the avian intestine cha nnel is strongly induced by varying NaCl intake.