Effect of age and dietary calcium on intestinal calbindin D-9k expression in the rat

The capacity of rats and humans to adapt to low dietary Ca by increasing intestinal Ca absorption declines with age. The intestinal calbindin-D-9k protein (calbindin) is thought to play a role in the transcellular transport of Ca across the mammalian intestine. The purpose of these studies was to determine the effect of age and diet on the expression of calbindin at the protein and mRNA levels. Young (2 month) and adult (12 month) male F344 rats were placed on either a high Ca diet (1.2%) or a low Ca diet (0.02%) for four weeks. In the duodenum, the level of intestinal calbindin protein induced by a low Ca diet was 8-fold higher in young rats compared to adult rats. In the ileum, expression of calbindin protein was only about 10% that of the duodenum. In addition, the adult ileum showed the same decreased adaptation to a low Ca diet that was seen in the adult duodenum. In both the duodenum and the ileum, the changes in calbindin protein expression were highly correlated with calbindin mRNA expression and the correlations in each segment were quantitatively similar. In the duodenum, the changes in calbindin protein levels were strongly correlated with both Ca transport and Ca uptake. This quantitative correlation suggests a role for calbindin protein in the age-related decline in Ca absorption. In the ileum, the decreased adaptation to a low Ca diet may also be important given the long transit time through the distal intestine. The changes in both intestinal segments may contribute to the negative Ca balance seen in adult rats fed a low Ca diet.