PHENOTYPIC EFFECTS OF ALDOSTERONE AND DEXAMETHASONE IN A SV40-TRANSFORMED MAMMALIAN CORTICAL ASCENDING LIMB CELL-LINE EXHIBITING MINERALOCORTICOID RECEPTORS

We have analyzed the functional and morphological effects of corticost eroid hormones in a SV40-transformed rabbit cortical-ascending-limb (C AL) cell line (RC.SV2, Vandewalle et al., 1989) having mineralocortico id (MR) and glucocorticoid (GR) receptors (Rafestin-Oblin et al., 1993 ). Both aldosterone and dexamethasone (5 x 10(-8) M) induced a marked increase in (H-3)ouabain binding (used to quantify membrane Na+-K+ ATP ase) detectable as early as 6 hours and maximal at 24 hours (+56-57%) (due to a 1.6-1.8-fold increase in cell membrane binding sites without Kd alteration), and significantly augmented the ouabain-sensitive com ponent of Rb+ influx. Triiodothyronine (T3, 10(-9) M) also stimulated ouabain binding by 21% but was not permissive for steroid action, wher eas 5 mug/ml insulin had no effect. Both steroid hormones, T3 and insu lin induced the formation of domes that was tightly correlated with ou abain binding (r = 0.949) except for insulin. The effects of aldostero ne and dexamethasone on cell monolayers and cell ultrastructure were, however, strikingly different as aldosterone induced a marked amplific ation of basolateral areas with appearance of large intercellular spac es, reminiscent of the changes observed in deoxycorticosterone-treated rats, whereas dexamethasone predominantly influenced cell height. Thi s discrepancy might be due to specific occupancy of MR and GR by aldos terone and dexamethasone, respectively, and/or to nongenomic effects o f dexamethasone. We have thus characterized a cell culture model makin g it possible to analyze the actions of mineralocorticoid and glucocor ticoid hormones in the mammalian kidney. (C) 1993 Wiley-Liss, Inc.