Aldosterone binding in isolated tubules I. Biochemical determination in proximal and distal parts of the rabbit nephron

Publisher Website
Google Scholar
Abstract
Microbiochemical methods were applied to proximal tubules (PCT) and a mixture of distal and cortical collecting tubules (D + C) of rabbit kidney to define aldosterone binding sites. For each experiment, after incubation of kidney pyramids with [3H]aldosterone ([3H]A), either alone or in the presence of an excess unlabled A, 100-150 mm of both categories of tubules were microdissected using collagenase. Specific binding was determined on the nuclear fraction of each sample. Aldosterone concentrations ranged from 2 .times. 10-9-4.5 .times. 10-8 M. No specific binding was detectable in PCT. Specific binding in D + C increased rapidly as a function of [3H]A concentration up to 5 .times. 10-9 M and then more slowly. No plateau was reached. Both the absence of saturation of the binding curve and the curvilinear aspect of the Scatchard plot suggested the presence of 2 binding sites, one of high affinity, presumably a mineralocorticoid site, and the other of lower affinity, possibly a glucocorticoid site. Evidently, the distal structures of the nephron, located in the cortex, are the main sites of binding of aldosterone and contain a high number of specific binding sites for this hormone.