Copper is taken up efficiently from plasma albumin by polarized mammary epithelial cell monolayers

Albumin, with a high affinity Cu binding site at its N‐terminus, is one of two main components of the exchangeable plasma Cu pool. Thus during lactation, when plasma Cu rapidly enters the mammary gland and milk, we would expect it to deliver Cu to cells in that organ. We thus examined the kinetics and uptake efficiency of Cu delivered by albumin to polarized human breast cell monolayers (PMC42), a model for mammary epithelium. For this, albumin was purified from human plasma by Cibacron Blue pseudoaffinity chromatography. Residual Cu was removed with histidine. Pure albumin loaded with one Cu/molecule (labeled with 64 Cu) was used in uptake studies with PMC42 cell monolayers (with tight junctions) grown in Transwells. Uptake of Cu from the di‐histidine and NTA complexes was compared. Cell uptake of 64 Cu from albumin increased with the Cu‐albumin concentration (Km of 13 uM), reaching a limited cell concentration, the excess going directly to the apical (milk) fluid. Cu‐his uptake was by non‐standard kinetics. Uptake of Cu from 1 and 10 uM Cu‐albumin was not inhibited by 50 uM Ag(I), a known inhibitor of CTR1. It was also not inhibited by 100–500 uM Fe(II), which might compete for entry through DMT1. Uptakes of Cu from his and NTA were similarly unaffected. We conclude that mammary epithelial cells receive Cu efficiently from albumin, but that neither CTR1 nor DMT1 are likely to be involved. Supported by USPHS Grant No. HD46949.