The 1,25D3-MARRS protein:: Contribution to steroid stimulated calcium uptake in chicks and rats

There are currently two main candidates for the membrane receptor for 1,25(OH)(2)D-3: the 1,25D(3)-MARRS protein/ERp57; and the classical VDR. The 1,25D(3)-MARRS protein is essential for hormone-stimulated phosphate and calcium uptake in chick intestinal cells, whereas the VDR is not. The 1,25D(3)-MARRS protein also shows a high degree of correlation with growth periods in which bone is rapidly formed, whereas the VDR does not. However, in rat enterocytes, both the 1,25D(3)-MARRS protein and the VDR play a role in the rapid, steroid-mediated uptake of phosphate or calcium. Therefore, the theory that alternate binding sites on the VDR for various analogs account for all membrane-initiated phenomena, is incorrect. (c) 2005 Elsevier lnc. All rights reserved.