Cloning and functional expression of a novel degenerin-like Na+ channel gene in mammals

1. A degenerate polymerase chain reaction (PCR) homology screening procedure was applied to rat brain cDNA in order to identify novel genes belonging to the amiloride-sensitive Na+ channel and degenerin (NC/DEG) family of ion channels. A single gene was identified that encodes a protein related to but clearly different from the already cloned members of the family (18-30% amino acid sequence identity). Phylogenetic analysis linked this protein to the group of ligand-gated channels that includes the mammalian acid-sensing ion channels and the Phe-Met-Arg-Phe-amide (FMRFamide)-activated Na+ channel. 2. Expression of gain-of-function mutants after cRNA injection into Xenopus laevis oocytes or transient transfection of COX cells induced large constitutive currents. The activated channel was amiloride sensitive (IC50, 1.31 mu M) and displayed a low conductance (9-10 pS) and a high selectivity for Na+ over K+ (ratio of the respective permeabilities, PNa+ / Pk+ greater than or equal to 10), all of which are characteristic of NaC/DEG channel behaviour. 3. Northern blot and reverse transcriptase-polymerase chain reaction (RT-PCR) analysis revealed a predominant expression of its mRNA in the small intestine, the liver (including hepatocytes) and the brain. This channel has been called the brain-liver-intestine amiloride-sensitive Na+ channel (BLINaC). 4. Corresponding gain-of-function mutations in Caenorhabditis elegans degenerins are responsible for inherited neurodegeneration in the nematode. Besides the BLINaC physiological function that remains to be established, mutations in this novel mammalian degenerin-like channel might be of pathophysiological importance in inherited nenrodegeneration and liver or intestinal pathologies.