Intestinal plasma membrane calcium pump protein and its induction by 1,25(OH)2D3 decrease with age

The plasma membrane Ca pump of intestinal absorptive cells has been proposed as a component in the vitamin D-dependent active transport of Ca. Because intestinal Ca transport declines with age, the purpose of this study was to determine if changes in Ca pump expression parallel this decline. Intestinal levels of the plasma membrane Ca pump protein were measured by Western blotting in Fischer 344 rats that were 2, 12, and 24 mo of age. Ca pump protein levels declined by 90% in the duodenum and 65% in the ileum between 2 and 12 mo of age, the time during which active Ca transport declines markedly. The effect of age on the induction of the Ca pump by 1,25-dihydroxyvitamin D-3 [1,25(OH)(2)D-3], the active metabolite of vitamin D, was determined. Rats were made deficient in 1,25(OH)(2)D-3 by feeding a high-strontium diet, and they were then dosed with 1,25(OH)(2)D-3 or vehicle at 48, 24, and 6 h. In 12-mo-old rats 1,25(OH)(2)D-3 induced duodenal Ca pump protein to only 39% and active Ca transport to 33% of that seen in 2-mo-old animals. These studies demonstrate that decreased expression of the plasma membrane Ca pump protein, along with calbindin protein, parallels the decline in intestinal Ca transport and its response to 1,25(OH)(2)D-3 with age.