Effect of lead exposure and accumulation on copper homeostasis in culturedC6 rat glioma cells

C6 rat glioma cells resemble rat astroglia in culture in that both cell typ es accumulate lead (Pb) intracellularly from the medium. As such, C6 cells are a model for Pb accumulation by the brain. In this study, an increase in intracellular Pb accumulation induced by p-chloromercuribenzoate (PCMB) af ter exposure to 10 mu M Pb acetate suggests a role for sulfhydryl groups in Pb retention. Stimulation of Pb accumulation by nifedipine suggests the en try of Pb into these cells by a novel path. Most of the intracellular Pb fr om exposure for 7 days to 1 mu M Pb was associated with high-molecular weig ht components in cytosol. Pb exposure increased the abundance of three prot eins with the following characteristics on two-dimensional gels: 81 kDa wit h pI of 5.6, 81 kDa with pi of 4.9, and 71 kDa with pi of 5.6. The levels o f five other proteins, ranging in size from 37-41 kDa with pls of 6.0-6.8 d eclined. Exposed C6 cells accumulated copper (Cu) intracellularly, and Cu a ccumulation after Pb exposure was shown by kinetic analysis with Cu-67 to r esult from an increased uptake and a decreased efflux for Cu. Pb-exposed ce lls also showed increased Cu binding to membranes, which is consistent with the increase of Cu uptake. These data indicate that intracellular Pb inter acts with high molecular weight proteins in C6 cells, and exposure also alt ers membrane transport properties for copper. (C) 1999 Academic Press.