Localization of the vitamin D-dependent calcium-binding protein in mammalian kidney

Abstract

The vitamin D-dependent calcium-binding protein (CaBP) was localized by immunocytochemistry in the rat and human kidney. In both species 80% of the cells lining the distal convoluted tubules contained CaBP. In the connecting segment and the initial collecting tubule of rat kidney, 50% of the cells was positive; in the outer medullary collecting duct only 15% was positive. In the human kidney, collecting ducts in medullary rays contained 50% positive cells, whereas in the rest of the medulla no positive cells were found. The CaBP-positive cells were identified as principal or clear cells by immunoelectron-microscopy, using the protein A-gold technique. Mitochondria-rich dark cells were negative. In principal cells, CaBP immunoreactive sites were found throughout the cytosol and the nuclear euchromatin. No preferential labeling of cellular membranes was found. The data show that CaBP-positive cells are present in tubular regions that are important in regulating the final excretion of calcium. However, the subcellular distribution of CaBP does not suggest a role in the initial transmembrane transport of Ca2+ but rather indicates an involvement in processes regulating intracellular calcium.

Control of calbindin‐D28K expression in developing mouse kidney

“…The functional reasons for this difference remain obscure. Constitutive expression throughout the embryonic collecting duct tree is quite different from the cortically restricted, 1,25(0H),D3-dependent pattern reported in the adult (Taylor et al, 1982;Rhoten and Christakos, 1981;Roth et al, 1982). It is, however, analogous to the constitutive expression in the drainage channel of embryonic mesonephros, the Wolffian duct.…”

“…In the adult kidney, ~a 1 b i n d i n -D~~~ is found in the principal sites of calcium uptake-the distal convoluted and connecting tubules (Rhoten and Christakos, 1981;Roth et al, 1981Roth et al, , 1982Taylor et al, 1982;Rhoten et al, 1985). Present even before birth, its reported 0 1994 WILEY-LISS, INC. embryonic location foretells the adult expression pattern.…”

Immunohistochemical determination of calbindin-d28k in the kidney of postnatal rats

“…These results represent a more extensive distribution of calbindin-D28k than tat found in the kidneys of any other animals investigated previously (Rhoten and Christakos, 1981;Taylor et al,1982;Schreiner et al, 1983;Rhoten et al, 1984) including the human (Roth et al, 1982). This statement is not strictly true as Rhoten et al (1982) reported immunoreactive calbindin-D28k in the medulla, including the ascending thick limb of the loop of Henle, as well as cortical labyrinth in neonatal rat kidney.…”

“…This distribution of calbindin-D28k has been described in the chicken, rat, rabbit and human kidney with only very li�le variation (Roth et al, 1982;Taylor et al, 1982;Christakos et al, 1997).…”

“…However there is no physiological evidence to support these observations. Since the bulk of Ca +2 reabsorption occurs in the proximal tubules and the ascending Henle's loops (Roth et al, 1982), this suggests that the renal calbindin-D28k does not play a role in the initial transmembrane transport of Ca +2 , but that it may be involved in active Ca +2 transport in the distal nephron and in those processes regulating intracellular Ca +2 levels. The localization of calbindin-D28k to a select population of cells supports the idea of an essential but highly specialized function for this protein in the kidney (Rhoten et al, 1986).…”