AJP - Regulatory, Integrative and Comparative Physiology, Vol 257, Issue 1 87-R95, Copyright © 1989 by American Physiological Society
Aldosterone binding sites along nephron of Xenopus and rabbit
A. Gnionsahe, M. Claire, N. Koechlin, J. P. Bonvalet and N. Farman
Institut National de la Sante et de la Recherche Medicale (INSERM) U 246, Departement de Biologie/SBCe, Gif-sur-Yvette, France.
Distal segment of several amphibians exhibits aldosterone-modulated ion
transport properties. On the other hand, A6 cells, derived from Xenopus
laevis (XL) kidney, are aldosterone sensitive. We examined the distribution
of aldosterone binding sites in isolated tubules of XL compared with
rabbit. After incubation with 2 nM [3H]aldosterone, microdissected tubular
segments from proximal (PT), distal straight segment (DST), and flask cell
collecting (CT) tubules from XL and from rabbit cortical thick ascending
limb (CTAL), connecting (CNT), and collecting (CCD) tubules were processed
for dry film autoradiography. In XL, specific nuclear labeling of type I
(mineralocorticoid) sites was restricted to DST. Labeling of type II
(glucocorticoid) sites was present all along the tubule. No specific
cytoplasmic labeling was observed, except for type II sites in PT. In the
rabbit, aldosterone binds to both type I and type II sites in the three
tubular segments studied. In these segments, the binding was about fourfold
higher than in DST of XL. These results bring direct evidence in
designating the distal tubule of amphibians as a target epithelium for
aldosterone. In addition, they suggest that A6 cell line may derive from
DST of the Xenopus nephron.
