Corticosteroid-Dependent Sodium Transport in a Novel Immortalized Mouse Collecting Duct Principal Cell Line

. The final control of sodium balance takes place in the cortical collecting duct (CCD) of the nephron, where corticosteroid hormones regulate sodium reabsorption by acting through mineralocorticoid (MR) and/or glucocorticoid (GR) receptors. A clone of principal CCD cells (mpkCCD c14 ) has been established that is derived from a transgenic mouse (SV40 large T antigen under the control of the SV40 enhancer/L-type pyruvate kinase promoter). Cells grown on filters form polarized monolayers with high electrical transepithelial resistance ( R T approximately 4700 Ω × cm 2 ) and potential difference ( P D approximately -50 mV) and have an amiloride-sensitive electrogenic sodium transport, as assessed by the short-circuit current method ( I sc approximately 11 μA/cm 2 ). Reverse transcription-PCR experiments using rat MR primers, [ 3 H]aldosterone, and [ 3 H]dexamethasone binding and competition studies indicated that the mpkCCD c14 cells exhibit specific MR and GR. Aldosterone increased I sc in a dose- (10 -10 to 10 -6 M) and time-dependent (2 to 72 h) manner, whereas corticosterone only transiently increased I sc (2 to 6 h). Consistent with the expression of 11β-hydroxysteroid dehydrogenase type 2, which metabolizes glucocorticoids to inactive 11-dehydroderivates, carbenoxolone potentiated the corticosterone-stimulated I sc . Aldosterone (5 × 10 -7 M)-induced I sc (fourfold) was associated with a three- to fivefold increase in α-ENaC mRNA (but not in those for β- or γ-ENaC) and three- to 10-fold increases in α-ENaC protein synthesis. In conclusion, this new immortalized mammalian CCD clonal cell line has retained a high level of epithelial differentiation and sodium transport stimulated by aldosterone and therefore represents a useful mammalian cell system for identifying the genes controlled by aldosterone.