ABSTRACT
The primary function of vitamin D, 1,25-dihy-droxyvitamin D3 (1,25(OH)2D3), in maintaining calcium homeostasis is through direct stimulation of intestinal transport, effects on calcium reabsorption in the kidney, and mobilization of mineral from bone. The protein in intestine and kidney whose synthesis is induced by 1,25(OH)2D3 is the calcium-binding protein, calbindin. This chapter focuses on how an understanding of the regulation of calbindin has resulted in a better understanding of the possible functional significance of calbindin. In the intestine, calbindin is localized in columnar epithelial cells and has been postulated to facilitate intracellular calcium translocation. Avian and mammalian renal calbindin-D28k is present in the principal cells of the distal tubule in which selective reabsorption of calcium is known to occur. Due to the significance of calbindin in the nervous system, it was important to determine the factors which could modulate the expression of this protein in brain.
