CALCIUM TRANSPORT AND ROLE OF VITAMIN D

Calcium transport has been studied in duodenum from rats either vitamin D-deficient or after treatment with vitamin D. Calcium is actively transported against an electrochemical potential gradient by an energy-dependent, cation-oriented process which is markedly enhanced by vitamin D and which does not require phosphate. Initial velocities of calcium uptake by intestinal mucosa are markedly affected by vitamin D at all dosage levels. This process is saturable with calcium (2.0 mm) and shows a requirement for oxygen. Intestinal mucosa from D-deficient rats behaves similarly, but demonstrates reduced rates of calcium uptake. The rate-limiting process in vitamin D deficiency appears to be the initial transfer of calcium across the brush border surface into the columnar epithelial cells. © 1969.