AJP - Renal Physiology, Vol 248, Issue 2 296-F307, Copyright © 1985 by American Physiological Society
1,25(OH)2D3 binding along the rat nephron: autoradiographic study in isolated tubular segments
C. Manillier, N. Farman, J. P. Bonjour and J. P. Bonvalet
1,25-dihydroxyvitamin D3 [1,25(OH)2D3] binding sites were studied along the
nephron of rats. The animals were pretreated with the diphosphonate EHDP at
doses that inhibit the endogenous production of 1,25(OH)2D3. A dry film
autoradiographic technique was applied to tubular segments isolated by
microdissection from kidneys incubated in vitro with various concentrations
(0.2-12 nM) of [3H]1,25(OH)2D3 in the presence or absence of an excess
unlabeled hormone (X200) in order to determine specific binding. Total,
nonspecific, and specific labeling were quantified by silver grain counting
over cytoplasmic and nuclear areas. Specific nuclear labeling appeared in
the cortical ascending limb and papillary collecting tubule at 1 nM. In the
distal tubule and, to a lesser extent, in the cortical collecting tubule a
specific nuclear labeling was also present, but only at higher
concentrations. No specific nuclear labeling was detected in the proximal
tubule. All along the nephron, a significant and nonspecific labeling was
observed in the cytoplasm, either alone or superimposed over the specific
nuclear labeling. In conclusion 1,25(OH)2D3 specific binding sites appear
to be localized mainly in the cortical ascending limb of the loop of Henle,
in the distal and cortical collecting duct, and in the papillary collecting
duct.
