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

1. A degenerate polymerase chain reaction (PCR) homology screening procedur e 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 b ut 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-sensin g ion channels and the Phe-Met-Arg-Phe-amide (FMRFamide)-activated Na+ chan nel. 2. Expression of gain-of-function mutants after cRNA injection into Xenopus laevis oocytes or transient transfection of COX cells induced large consti tutive 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 tha n or equal to 10), all of which are characteristic of NaC/DEG channel behav iour. 3. Northern blot and reverse transcriptase-polymerase chain reaction (RT-PC R) analysis revealed a predominant expression of its mRNA in the small inte stine, the liver (including hepatocytes) and the brain. This channel has be en called the brain-liver-intestine amiloride-sensitive Na+ channel (BLINaC ). 4. Corresponding gain-of-function mutations in Caenorhabditis elegans degen erins are responsible for inherited neurodegeneration in the nematode. Besi des the BLINaC physiological function that remains to be established, mutat ions in this novel mammalian degenerin-like channel might be of pathophysio logical importance in inherited nenrodegeneration and liver or intestinal p athologies.