Vitamin D and Intestinal Calcium Transport: Facts, Speculations and Hypotheses

Abstract

The intestinal absorption of Ca2+ occurs by both a saturable, transcellular process and a nonsaturable, paracellular path. The transcellular path is a multistep process, comprised of the transfer of luminal Ca2+ into the enterocyte, the translocation of Ca2+ from point of entry (the microvillus border or membrane) to the basolateral membrane, and the active extrusion from the cell into the circulatory system. Each step in the transcellular movement of Ca2+ has a vitamin D-dependent component. The paracellular path also appears to be affected by vitamin D status. This review emphasizes some aspects of the Ca2+ absorptive process that require resolution and/or further experimental support. The following are discussed: evidence for participation in the active transport of Ca2+ by all segments of the small intestine; a hypothetical model for the feedback control of entry of luminal Ca2+; the current views on vitamin D-dependent movement of Ca2+ through the cytosolic compartment of the enterocyte; the stimulated synthesis of the plasma membrane Ca2+ pump and its gene expression by vitamin D; and the vitamin D-dependency of the paracellular transfer of Ca2+ with a comment on the physiological significance of the rapid response of the Ca2+ absorptive system in vitamin D-replete animals to 1,25-dihydroxyvitamin D.

The epithelial calcium channels TRPV5 and TRPV6: regulation and implications for disease

“…The extracellular Ca 2+ concentration is tightly controlled by the concerted action of intestinal Ca 2+ absorption, exchange of Ca 2+ from bone and renal Ca 2+ reabsorption (Fukugawa and Kurokawa 2002;Hurwitz 1996). Both in kidney and intestine, Ca 2+ can (re)enter the extracellular fluid by passive paracellular as well as active transcellular Ca 2+ transport (Bindels 1993;Wasserman and Fullmer 1995).…”

“…1; Hoenderop et al 2000b;Wasserman and Fullmer 1995). Active absorption of dietary Ca 2+ occurs primarily in the proximal small intestine, while in kidney active Ca 2+ reabsorption is restricted to the distal convoluted tubule (DCT) and the connecting tubule (CNT; Bronner et al 1986;Friedman and Gesek 1995).…”

Vitamin D supplementation and strontium ranelate absorption in postmenopausal women with low bone mass

“…Vitamin D is an important factor in Ca absorption (7,10,11,12,13,14,15). As very few foods naturally contain vitamin D and foods are not fortified worldwide, the major source for most humans is exposure to sunlight (16,17).…”

“…A number of studies suggest that vitamin D status is a determinant of Ca absorption (10,11,12,13). While the factors that regulate Sr have not yet been determined, they are assumed to be similar to those that regulate Ca metabolism (7,10,26).…”

Contribution of Intestinal Calcium Absorption to 1,25-Dihydroxyvitamin D3-Induced Calcium Action in the Total Parenteral Nutrition Rat

“…1,25(OH) 2 D 3 directly increases intestinal Ca absorption through up-regulation of Ca transport proteins (Bronner et al, 1986;Hoenderop et al, 2004). The role of 1,25(OH) 2 D 3 in the intestinal Ca absorption is established, and 1,25(OH) 2 D 3 produces two types of effects, one dependent on gene expression and protein synthesis (genomic action), and a more rapid response not dependent on gene activation (nongenomic action) (Bronner, 2003;Christakos et al, 2003;Hurwitz, 1996;Lee et al, 1990;Wasserman and Fullmer, 1995).…”