Corticosteroid-dependent sodium transport in a novel immortalized mouse collecting duct principal cell line

Abstract

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 x cm2) 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/cm2). Reverse transcription-PCR experiments using rat MR primers, [3H]aldosterone, and [3H]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 x 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.