Peptide block of constitutively activated Na⁺ channels in Liddle's disease

Hypertension is a multifactorial disorder that results in an increased risk of cardiovascular and end-stage renal disease. Liddle's disease represents a specific hypertensive disease and expresses itself in the human population as an autosomal dominant trait. Recent experimental evidence indicates that patients with Liddle's disease have constitutively active amiloride-sensitive Na⁺ channels and that these channels are phenotypically expressed in lymphocytes obtained from normal and affected members of the original Liddle's kindred. Linkage analysis indicates that this disease results from a deletion of the carboxy-terminal region of the β-subunit of a recently cloned epithelial Na⁺ channel (ENaC). We report the successful immunopurification and reconstitution of both normal and constitutively active lymphocyte Na⁺ channels into planar lipid bilayers. These channels display all of the characteristics typical of renal Na⁺ channels, including sensitivity to protein kinase A phosphorylation. We demonstrate that gating of normal Na⁺ channels is removed by cytoplasmic trypsin digestion and that the constitutively active Liddle's Na⁺ channels are blocked by a β- or γ- ENaC carboxy-terminal peptide in a GTP-dependent fashion.