Characterization of the ion transport responses to ADH in the MDCK-C7 cellline

The Madin-Darby canine kidney (MDCK) cell line expresses many characteristi cs of the renal collecting duct. The MDCK-C7 subclone forms a high-resistan ce, hormone-responsive model of the principal cells, which are found in dis tal sections of the renal tubule. The electrophysiological technique of sho rt-circuit current measurement was used to examine the response to antidiur etic hormone (ADH) in the MDCK-C7 clone. Three discrete electrogenic ion tr ansport phenomena can be distinguished temporally and by the use of inhibit ors and effecters. Initially the cells exhibit anion secretion through the cystic fibrosis transmembrane conductance regulator (CFTR). The presence of CFTR was confirmed by immunoprecipitation followed by Western blotting. Th e CFTR-mediated anion secretion is transient and is followed, in time, by a verapamil- and Ba2+-sensitive anion secretion or cation absorption and, fi nally, by Na+ reabsorption via epithelial Na+ channels (ENaC). In contrast to other studies of MDCK cells, we see no indication that the presence of C FTR functionally inhibits ENaC. The characterization of the various ion tra nsport phenomena substantiates this cell line as a model renal epithelium t hat can be used to study the hormonal and metabolic regulation of ion trans port.