Aldosterone Receptors in Rabbit Renal Cortex and Red Medulla*

Publisher Website
Google Scholar
Abstract
[3H]Aldosterone-specific binding sites were assessed in rabbit renal cortex, red medulla, and papilla slices using Scatchard analyses. Only cortex and red medulla contained high affinity sites for aldosterone (Kd = 3.0–3.7 × 10-9 M; 37 C). The regression slopes determined for these sites were not statistically different from each other. In contrast, papilla slices contained a low affinity site (Kd = ∼2.8 × 10-8m) whose regression slope was not statistically different from a low affinity site seen in both cortex and red medulla. The maximum number of high affinity sites in cortex and red medulla was computed to be 1.5 and 0.9 × 10-14 mol [3H]aldosterone/mg protein, respectively. Competition analyses indicated that the rank order of inhibition of [3H]aldosterone-bound cortical and red medulla sites by various corticoids was aldosterone > corticosterone > dexamethasone. DE-52-Cellulose chromatography of [3H]aldosterone-labeled renal complexes revealed that both cortex and red medulla aldosterone-specific binding proteins eluted at the same conductivity (equivalent to 0.3 M KC1) and only after elution of both plasma [3H]corticosterone-labeled binding proteins (0.1–0.15 M KC1) and renal cortical [3H]dexamethasone-labeled glucocorticoid complexes (-0.23 M KC1). Furthermore, when sodium molybdate, a phosphatase inhibitor, was added to DE-52-cellulose column buffers, labeled serum glucocorticoid, renal glucocorticoid, and renal mineralocorticoid-specific complexes eluted at a lower conductivity. However, both cortex and red medulla [3H]aldosterone-labeled complexes again eluted at the same conductivity (equivalent to ∼0.24 M KC1). These findings are consistent with the suggestion that mineralocorticoid target cells exist in both the cortex and red medulla of rabbit kidney, as evidenced by the presence of mineralocorticoid receptors. Finally, the addition of 20 mM sodium molybdate prevented the thermal (20 C) inactivation of unlabeled cortical and medullary mineralocorticoid receptors compared to a 40-53% loss of binding activity during a 60-min incubation at 20 C in the presence of 20 tnM sodium chloride. (Endocrinology106: 611, 1980)