Calbindin D9k is not required for 1,25-dihydroxyvitamin D3-mediated Ca2+ absorption in small intestine.

The exact role of calbindin D9k in vitamin D-mediated calcium absorption has been debated but remains unsettled. In 129/OlaHsd mice, calbindin D9k was found highest in duodenum (36-50%) and kidney (24-34%) followed by stomach, lung and uterus. Age does not affect the relative distribution of calbindin D9k but it does decline with age in duodenum of both male and female 129/Ola mice. Recently, we produced a null calbindin D9k mutant 129/OlaHsd mouse; this mouse proved to be indistinguishable from the wild-type in phenotype and in a serum calcium level regardless of age or gender. We have now examined directly whether the mutant mouse can absorb calcium from the intestine in response to the active form of vitamin D. The calbindin D9k null mutant mouse is fully able to absorb calcium from the intestine in response to 1,25-dihydroxyvitamin D3. It is, therefore, clear that calbindin D9k is not required for vitamin D-induced intestinal calcium absorption.