Albumin facilitates zinc acquisition by endothelial cells

Albumin has long been observed to have a marked influence on the delivery of zinc to cells, but the mechanism of the interaction remains elusive. We examined whether albumin facilitates the acquisition of zinc by endothelial cells. Cultures of endothelial cells were used to analyze binding and acquisition of zinc and albumin to test this interaction. Our results indicate that albumin plays a role in facilitating the physiological delivery of zinc to endothelial cells. Albumin receptors that preferentially recognize albumin molecules carrying a zinc atom were demonstrated on the endothelial cell surface. Endocytosis is instrumental in albumin uptake, which was also consistently true of zinc uptake. Zinc and albumin were acquired by the cells in a 1:1 molar stoichiometry during the first 20 min of incubation in a medium with equimolar concentrations of zinc and albumin. The amount of albumin associated with the cells stabilized after 30 min, whereas the amount of zinc continued to increase. One possible explanation for this result is that a physiological route for zinc delivery into endothelial cells is by co-transport with albumin via receptor-mediated endocytosis.