Vasopressin-stimulated CFTR Cl⁻ currents are increased in the renal collecting duct cells of a mouse model of Liddle's syndrome

Abstract

Liddle's syndrome is a genetic form of hypertension linked to Na⁺ retention caused by activating mutations in the COOH terminus of the β or γ subunit of the epithelial sodium channel (ENaC). In this study, we used the short-circuit current (I_sc) method to investigate the effects of deamino-8-d-arginine vasopressin (dDAVP) on Na⁺ and Cl⁻ fluxes in primary cultures of cortical collecting ducts (CCDs) microdissected from the kidneys of mice with Liddle's syndrome carrying a stop codon mutation, corresponding to the β-ENaC R₅₆₆ stop mutation (L) found in the original pedigree. Compared to wild-type (+/+) CCD cells, untreated L/+ and L/L CCD cells exhibited 2.7- and 4.2-fold increases, respectively, in amiloride-sensitive (Ams) I_sc, reflecting ENaC-dependent Na⁺ absorption. Short-term incubation with dDAVP caused a rapid and significant increase (∼2-fold) in Ams I_sc in +/+, but not in L/+ or L/L CCD cells. In sharp contrast, dDAVP induced a greater increase in 5-nitro-2-(3-phenylpropamino)benzoate (NPPB)-inhibited apical Cl⁻ currents in amiloride-treated L/L and L/+ cells than in their +/+ counterparts. I_sc recordings performed under apical ion substituted conditions revealed that the dDAVP-stimulated apical secretion of Cl⁻, which was absent in cultured CCDs lacking CFTR, was 1.8-fold greater in L/+ and 3.7-fold greater in L/L CCD cells than in their +/+ CCD counterparts. After the basal membrane had been permeabilized with nystatin and a basal-to-apical Cl⁻ gradient had been imposed, dDAVP also stimulated larger Cl⁻ currents across L/L and L/+ CCD layers than +/+ CCD layers. These findings demonstrate that vasopressin stimulates greater apical CFTR Cl⁻ conductance in the renal CCD cells of mice with Liddle's syndrome than in wild-type mice. This effect could contribute to the enhanced NaCl reabsorption observed in the distal nephron of patients with Liddle's syndrome.