Immunocytochemical Study of Calbindin D(28k) Positive Cells in the Developing Rat Kidney

Park, Eun Young; Lee, Hyun Wook; Song, Hyun Kuk; Hwang, Jin Sun; Kim, Wan Young; Kim, Jin

Abstract

Calbindin D(28k),a calcium binding protein,is found in various tissues,including some cells in the distal nephron.It plays an important role in the regulation of calcium reabsorption. We previously reported the expression of calbindin D(28k) in adult rat kidney.However,the exact time of expression during differentiation in the embryonic kidney is not known.During development,intercalated cells are deleted from the medullary collecting duct by two distinct mechanisms.However,the reason for the different modes of cell death is not known.As calbindin is reported to protect cells against apoptosis,we examined the expression of calbindin D(28k) in the developing rat kidney.Kidneys from 16-,17-,18-and 20-day-old fetuses and 1-,3-,5-,7-,14-and 21-day-old pups and adult Sprague awley rats were processed for immunohistochemistry using a monoclonal antibody against calbindin D(28k) .Intercalated cells were identified by immunostaining for H+ -ATPase and by electron microscopy.Calbindin D(28k) immunoreactivity first appeared in subpopulations of cells in the connecting tubule and medullary collecting duct in the 17-day-old fetus.In the connecting tubule,calbindin D(28k) was expressed only in H+ -ATPase negative connecting tubule cells,and there was no labeling of intercalated cells.In the medullary collecting duct,calbindin D(28k) immunostaining was observed in a few cells with apical H+ -ATPase,characteristic of type A intercalated cells.The numbers of calbindin D(28k) -positive type A intercalated cells increased from day 18 of gestation.In contrast,there was little or no calbindin D(28k) immunoreactivity in the type B intercalated cells or principal cells.During the first two weeks after birth,calbindin D(28k) -positive type A intercalated cells were lost from the terminal part of the medullary collecting duct by simple extrusion. After two weeks,calbindin D(28k) immunostaining decreased in the type A intercalated cells throughout the medullary collecting duct.However,the immunoreactivity of calbindin D(28k) in the cortical collecting duct was increased in some of the type A intercalated cells and the adult pattern was observed in 21-day-old pups.Thus,we propose that the different expression of calbindin D(28k) in type A and type B intercalated cells may be responsible-at least partly-for the different modes of cell death demonstrated in these cells during kidney development.