Ion microscopic imaging of calcium during 1,25-dihydroxyvitamin D-mediated intestinal absorption

Abstract

A combination of ion microscopic and conventional radionuclide techniques was employed to investigate the temporal-spatial dynamics of 1,25-dihydroxyvitamin D3 [1,25(OH)2D3]-stimulated intestinal calcium (Ca) absorption. At varying times following the administration of a single intravenous dose of 1,25(OH)2D3 to vitamin D-deficient chicks, transepithelial transport and tissue retention of Ca were quantitated in vivo, using the ligated duodenal loop technique and 47Ca as the tracer. The localization of Ca in the intestinal tissue during absorption was monitored by ion microscopy, using the stable Ca isotope, 44Ca, as the absorbed species. There was little transepithelial absorption of Ca in the vitamin D-deficient animals despite a substantial tissue accumulation of luminally derived Ca, the latter localizing predominantly in the brush border region of the enterocyte, as shown by the 44Ca-ion microscopic images. The early (30 min-1 h) response to 1,25(OH)2D3 was an increased tissue uptake of luminal 47Ca, which also primarily associated with the brush border region, again as shown by ion microscopy. At 2-4 h after the 1,25(OH)2D3 dose, there was a progressive redistribution of Ca from the brush border region throughout the cytoplasm and into the lamina propria. At 8-16 h, 47Ca absorption was maximal and 44Ca was sparsely distributed in the intestinal tissue. 47Ca absorption gradually declined and reached pre-dose levels by 72 h. At this time, tissue 44Ca was again largely limited to the brush border region. These results provide support for the multiple actions of 1,25(OH)2D3 on the intestinal Ca absorption process. The ion microscopic images provided unique information on the specific time-dependent changes in the tissue localization of Ca during the process of its intestinal absorption as affected by 1,25(OH)2D3.

Immunocytochemical and In Situ Hybridization Studies of the Distribution of Calbindin D9kin the Bovine Placenta Throughout Pregnancy

“…The asymmetric (higher apical than basal) cytoplasmic distribution of CBP that we find in the cow trophoblast cells has also been reported in chicken enterocytes for 28CBP (Thorens et al 1982;Nemere et al 1991) and correlates with the initial localization of 47 Ca uptake by ion microscopy in this system (Fullmer et al 1996). It could represent a transient store or a device to enhance the rate of facilitated diffusion.…”

Duodenal calcium absorption in vitamin D receptor–knockout mice: Functional and molecular aspects

“…By contrast, duodenal CaT1 and, to a lesser degree, ECaC RNA levels were dramatically and consistently down-regulated in the Tokyo and the Leuven KOs. Until recently, the unidentified calcium influx mechanism was not regarded as primordial, as calcium entered into the enterocyte even in the absence of vitamin D (15,24,34). Surprisingly, the present duodenal gene expression pattern indicates that, among the candidate calcium-transporting genes, only CaT1 and ECaC are severely impaired in VDR-KO mice.…”

“…This may imply a regulatory role for the epithelial calcium channels in active calcium absorption or a more complex regulation driven by the interaction between calcium influx and calbindin-D 9K . The permanent activation of these channels may indeed require the immediate intracellular uptake of each calcium molecule delivered through the channel by calbindin-D 9K , with subsequent mobilization of calcium toward the basolateral membrane (24,34,35). In this view, the major down-regulation of CaT1 and ECaC expression combined with a reduced calbindin-D 9K expression may contribute to the more profound hypocalcemia and reduced calcium in bone of the Tokyo KO on the normal diet.…”

1,25-Dihydroxyvitamin D3 Controls a Cohort of Vitamin D Receptor Target Genes in the Proximal Intestine That Is Enriched for Calcium-regulating Components

“…Deletion studies, however, have revealed that neither protein is essential for vitamin D-mediated calcium uptake as the loss of the genes for calbindin D9K or calbindin D28K expression did not alter intestinal sensitivity to 1,25(OH) 2 D 3 (14 -16). Rather, these proteins were eventually deemed to be calcium-sensitive buffer components likely involved in the shuttling of calcium to organelles within the cytoplasm (17). Interestingly, although both S100g and Calb1 were identified early on as direct targets of vitamin D action (18,19), the molecular details through which their expression is enhanced by 1,25(OH) 2 D 3 is currently unclear.…”