HUMAN FETAL ENDOTHELIAL-CELLS ACQUIRE ZINC(II) FROM BOTH THE PROTEIN-BOUND AND NONPROTEIN BOUND POOLS IN SERUM

To help determine physiologically important routes by which zinc (Zn) is acquired by human fetal vascular endothelium, the authors incubated cultured umbilical vein endothelial cells with Zn-65(II)-tracer label ed human fetal whole serum, ultrafiltrate (containing low molecular ma ss serum zinc complexes), and dialyzed serum (containing protein-bound zinc). Zinc from whole serum and from both serum fractions entered a rapidly labeled cellular compartment, removable by edetic acid (EDTA), representing Zn bound to the outside cell surface, and accumulatively , an EDTA-resistant compartment-probably largely internalized Zn. Entr y of Zn into the EDTA-resistant pool from both serum fractions was str ongly temperature-dependent, and was not via the EDTA-sensitive pool. Entry from the ultrafiltrate was resolvable into high affinity saturab le, and non- (or hardly-) saturable components. Transfer from the dial yzed serum fraction was not significantly saturable, but only partiall y accounted for by nonspecific pinocytosis. Thus, Zn is obtained by fe tal vascular endothelium partly from low molecular mass serum species, probably through at least one carrier-mediated membrane transport sys tem; but also from Zn complexed with serum protein, via at least one m etabolism-related route.