Module 7: Figure intestinal Ca2+ reabsorption
Control of Ca2+ reabsorption by intestinal cells.
Transport of Ca2+ across intestinal cells occurs through both active and passive transport mechanisms. The paracellular pathway depends upon the passive flow of Ca2+ through the tight junctions. The active transcellular pathway depends upon entry across the apical membrane through vanilloid transient receptor potential 6 (TRPV6) channels, facilitated diffusion across the cell associated with calbindin D-9k and then extrusion from the cell by plasma membrane Ca2+-ATPase 1b (PMCA1b) pumps located on the basolateral membrane. 1,25-Dihydroxyvitamin D3 [1,25(OH)2D3] enhances this transcellular pathway by increasing the expression of these three main components.