Transepithelial transport of retinol is linked to retinol-binding protein (RBP), which is taken
up and also synthesized in a number of epithelia. By immunocytochemistry of human, rat,
and mouse renal proximal tubules, a strong staining in apical endocytic vacuoles,
lysosomes, endoplasmic reticulum, Golgi, and basal vesicles was observed, in accordance
with luminal endocytic uptake as well as a constitutive synthesis and basal secretion of RBP.
Analysis of mice with target disruption of the gene for the major endocytic receptor of …