Specific aldosterone binding in rat kidney and parotid

The specific intracellular binding of [³H]-aldosterone was studied in tissue slices of kidney and parotid from adrenalectomized rats. Specific aldosterone binding proteins were isolated from (1) cytosol by G-50 Sephadex chromatography, (2) nuclei by an initial osmotic shock procedure (2.2 M sucrose followed by extraction with 0.1 M tris-3 mM CaCl₂ and 50% (NH₄)₂SO₄ precipitation = "soluble nuclear") and (3) nuclei by a subsequent 04 M KCl-3 mM CaCl₂ extraction and 50% (NH₄)₂SO₄ precipitation ("chromatin bound"). In both tissues, the time course of uptake into the three intracellular compartments was studied by incubation at 25°C for 0-4 h with 5.2 × 10^-9 m [³H]-aldosterone. Both kidney and parotid show the same three-step time sequence of specific intracellular binding-first cytosol, then soluble nuclear, and then chromatin bound. The time course and extent of [³H]-aldosterone binding in kidney slices was unaffected by concentrations of cycloheximide sufficient to lower protein synthesis by 67%. Cytosol binding proteins in kidney and parotid have an identical affinity for aldosterone but their concentration per g wet weight tissue in the kidney is twice that in the parotid. Despite this difference in cytosol donor concentration, and the presumed identity of active sites, levels of intranuclear [³H]-aldosterone-protein complexes are considerably higher in parotid than in kidney (soluble nuclear × 2, chromatin bound × 15).