1,25-Dihydroxyvitamin D-stimulated calmodulin binding proteins: a sustained effect on distal tubules

The tubular localization of 1,25-dihydroxyvitamin D[1,25(OH)(2)D(3)]-stimulated calmodulin binding proteins (CaMBP-Ds) in the rat kidney and the specificity of their induction were characterized to better understand renal responses to protracted 1,25(OH)(2)D(3) treatment in vivo. None of the other hormones tested (parathyroid hormone, calcitonin, estradiol-17beta, testosterone, progesterone, hydrocortisone, or dexamethasone) stimulated the CaMBP-Ds, whereas maximal 1,25(OH)(2)D(3) stimulation occurred after a 5- to 7-day treatment with 100 ng/day 1,25(OH)(2)D(3). With the exception of the more ubiquitously distributed CaMBP-D150, the CaMBP-Ds were localized in distal, but not proximal, tubule preparations. 1,25(OH)(2)D(3) induction of vitamin D receptors and the CaMBP-Ds was similar with respect to dose-response and time course. Finally, the CaMBP-Ds remained elevated for at least 4 wk after 1,25(OH)(2)D(3) withdrawal. Because the vitamin D-stimulated renal CaMBP-Ds are principally proteins of the distal tubule, they may be associated with renal regulation of Ca(2+) homeostasis. The sustained induction of CaMBP-Ds is important in addressing the question of whether their induction is a function of normal Ca(2+) homeostasis or a pathophysiological consequence of hypervitaminosis D and hypercalcemia.