The mechanism of zinc uptake by cultured rat liver cells.

Abstract

1. The initial rate of 65Zn uptake into cultured rat hepatocytes has been measured over a range of Zn2+ concentrations from 3 x 10(‐10) M to 5 x 10(‐6) M. Histidine and albumin were used to buffer Zn2+ ions at concentrations below 1 x 10(‐6) M. 2. The results suggest there are two mechanisms for Zn2+ uptake; a high‐affinity, saturable pathway, with a maximum velocity (Vmax) of 20‐30 pmol (mg protein)‐1 min‐1 and a Michaelis‐Menten constant (Km) of about 2 x 10(‐9) M Zn2+ (with histidine), and a low‐affinity, linear pathway, that only makes a significant contribution to Zn2+ uptake at Zn2+ concentrations above 1 x 10(‐6) M. 3. Transport via the high‐affinity pathway is dependent on the concentration of Zn2+ ions and not on the concentrations of Zn(2+)‐ligand complexes, suggesting that Zn2+ is the transported species. 4. The affinity of the saturable pathway for Zn2+ is slightly lower in the presence of albumin, with a Km of about 1.3 x 10(‐8) M. The reason for this is uncertain. © 1994 The Physiological Society