Figure 3. Schematic representation of the role of megalin in renal tubular 25 OH vitamin D reabsorption. Megalin is a multifunctional brush border membrane receptor expressed in the proximal renal tubule. It enables endocytic reabsorption of 25 OH vitamin D (calcidiol) filtered by the glomerulus and the subsequent synthesis of 1,25 diOH vitamin D (calcitriol) by mitochondrial 1-a 25 OH vitamin D hydroxylase. After Nykjaer et al (49).