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

Liddle's syndrome is a genetic form of hypertension linked to Na-divided by retention caused by activating mutations in the COOH terminus of the beta or gamma subunit of the epithehai 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-divided by 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 beta-ENaC R-566 stop mutation (L) found in the original pedigree. Compared to wild-type (divided by/divided by) 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-divided by 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 per-formed 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/divided by 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/divided by CCD layers than divided by/divided by 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.