Immunocytochemical localization of vitamin D-dependent calcium binding protein in mammalian nephron.

Immunoreactive calcium binding protein (iCaBP) has been localized in the rat nephron using the unlabeled antibody peroxidase-antiperoxidase immunocytochemical technique. Kidneys from normal young adult, vitamin D-deficient, and 12 day old rats were prepared by either freeze-substitution or 1% glutaraldehyde-Bouin's fixation. CaBP was localized with rabbit antiserum to chicken vitamin D-dependent intestinal CaBP. iCaBP was found specifically in the distal convoluted tubules (DCT); however, not all cells of the DCT were positive. In adult nephrons, a few scattered cells apparently belonging to the collecting tubules were positive. In the neonatal nephrons, there was also localization of iCaBP to the thick limb of Henle, suggesting a difference in the regulation of intracellular calcium during maturation. Proximal tubules, renal corpuscles, macula densa, and thin limbs of Henle gave no specific localization of iCaBP. These results present for the first time the localization of iCaBP in the mammalian nephron both in the neonate and in the young adult.