Molecular Cloning and Functional Expression of a Novel Amiloride-sensitive Na⁺ Channel *

We have isolated a cDNA for a novel human amiloride-sensitive Na channel isoform (called δ) which is expressed mainly in brain, pancreas, testis, and ovary. When expressed in Xenopus oocytes, it generates an amiloride-sensitive Na⁺ channel with biophysical and pharmacological properties distinct from those of the epithelial Na⁺ channel, a multimeric assembly of α, β, and γ subunits. The Na⁺ current produced by the new δ isoform is increased by two orders of magnitude after coexpression of the β and γ subunit of the epithelial Na⁺ channel showing that δ can associate with other subunits and is part of a novel multisubunit ion channel.