Transport of Calcium

Role of calbindin‐D9k in buffering cytosolic free Ca2+ ions in pig duodenal enterocytes.

“…This indicates that this vitamin D-dependent Ca2+ binding protein constitutes up to 2% of total soluble protein associated with the cells. These data are consistent with previous results from the duodenum of birds and mammals (Nemere & Norman, 1991). Since the density of the mucosal tissue was approximately 1 g cm-3, and, assuming that the mucosa contains 70 % cytosolic water by weight (Feher, Fullmer & Wasserman, 1992), the average calbindin-D9k concentration in normal pigs would be -250 uM and g63um in pigs with calcitriol deficiency.…”

“…Under normal feeding conditions, enterocytes of the small intestine are exposed to high concentrations of Ca2+. For maintained at very low levels, because firstly, it is well established that higher [Ca2+]i levels have adverse effects on a variety of intracellular metabolic processes, and secondly, as with other cell types, enterocytes use [Ca2+]i as a second messenger (Nemere & Norman, 1991). In Ussing chamber experiments, 20 pmol Ca2+ has been shown to be transported per second by active mechanisms across a 1 cm2 sheet of duodenal tissue (Schrdder et al 1993) with an approximately 50,um length of absorbing cells (Kretsinger, Mann & Simmonds, 1982 In the present study, mucosal calbindin-D9k concentrations of about 20 and 5,ug (mg soluble protein)-' were determined in con-and def-animals, respectively.…”

“…However, particularly in enterocytes of the upper small intestine, which are challenged continuously by high daily rates of Ca2+ absorption and are therefore exposed to high concentrations of CaP, the mechanisms involved in maintaining [Ca2+]i at a low level are not well defined. Transcellular active Ca2P transport is facilitated in the presence of the vitamin Ddependent Ca2P-binding protein calbindin-D9k, which is under the control of calcitriol (Schroder, Kaune, Schlumbohm, Breves & Harmeyer, 1993), and it has been proposed that calbindin-D9k could also function as a protective buffer against free Ca2P ions (Nemere & Norman, 1991). In a previous in vitro study with Ussing chambers using isolated, intact epithelia of the small intestine of pigs with calcitriol deficiency and with low non-physiological mucosal calbindin-D9k concentrations (Fox, Maunder, Randall & Care, 1985), a greater stimulation of net electrogenic ion transport rates by certain secretagogues such as theophylline and A23187 was demonstrated (Schroder, Kaune & Harmeyer, 1991).…”

Time dependency of 1,25(OH)2D3 induction of calbindin mRNA and calbindin expression in chick enterocytes during their differentiation along the crypt-villus axis

“…Upregulation of calbindin expression correlates well with the maintenance of high levels of calcium absorption in the small intestine [I, 15,161. Calbindin in this case is thought to facilitate calcium transport indirectly by acting as an intracellular buffer [13].…”

Culture and transformation of embryonic quail duodenal epithelial cells

“…Avian intestinal cells are useful model systems for studying Ca2+-transport, actions of hormonal vitamin D 3 [1,25(OH)2D3], and intestinal parasitic organisms (6,7). Our interest in the past has been to study the genomic and nongenomic mechanisms of action of 1,25(OH)2D 3 vitamin D 3 on the absorptive or enterocyte cells of the avian duodenum (4,5).…”