Binding of aldosterone to cytoplasmic and nuclear receptors of the rabbit kidney

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Abstract
The binding characteristics of [3H]aldosterone ([3H]A) in the rabbit kidney were compared with those described in other species, and experimental conditions suitable for both the isolation of renal tubules and the retention of aldosterone receptors were examined. Specific binding of [3H]A to cytoplasmic (C) and nuclear (N) receptors was determined on kidney slices incubated at +30 degrees C in rabbits fed a low K+-high Na+ diet. Results indicate the presence of at least two binding sites in N fractions, one of high affinity (Kd (I)) 1.8 X 10(-8) M) and low capacity (Nmax (I) 4.6 X 10(-14) mol/mg DNA), called type I sites, and the other of lower affinity (Kd (II) 8.9 X 10(-8) M) and more numerous sites (Nmax (II) 13.1 X 10(-14) mol/mg DNA). Competition studies showed that type I sites have higher affinity for [3H]A than for other steroids. Incubation at +37 degrees C resulted in a loss of type I sites. In adrenalectomized rabbits the C binding was improved but not the N binding (Kd (I) 1.2 X 10(-8) M; Kd (II) 5.6 X 10(-8) M). In rabbits treated with aminoglutethimide, an inhibitor of steroid synthesis, the N binding was lower than in other series. It was concluded that 1) [3H]A binding in the rabbit kidney does not differ from that described in other species; 2) a low K+-high Na+ diet is a satisfactory condition for study of [3H]A binding; and 3) incubation at +30 degrees C, a temperature necessary for microdissection procedures, is suitable for aldosterone binding studies.