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.