Calbindin-D28K in the Circulatory System of the Chick1

Publisher Summary This chapter discusses about calbindin-D, the vitamin D-induced calcium-binding protein (CaBP), which was first identified in the intestinal mucosa of the chick, and has since been found in a number of tissues and in several different species. The effect of duodenal calcium absorption on the CaBP concentration in the venous blood draining the gut was determined. The calcium concentration in mesenteric venous serum was significantly greater in those chicks receiving the normal or the high calcium diets as compared to the low calcium group. The transfer of CaBP from the interstitial fluid into the lumen of the vein could be a function of the well characterized structural features of the microcirculation. These include the existence of bidirectional endocytotic–exocytotic cycles, and fenestrations in the capillary and the venous walls. The function of CaBP in peripheral nerve cells of the intestinalis nerve is unknown. Its presence in the varicosities in the axon suggests a role in neurotransmitter release because these regions of the axon are thought to be sites of secretion of neurotransmitters.