EFFECTS OF CELLULAR COPPER CONTENT ON COPPER UPTAKE AND METALLOTHIONEIN AND CERULOPLASMIN MESSENGER-RNA LEVELS IN MOUSE HEPATOCYTES

The intracellular copper content of mouse hepatocytes has been altered by incubating with either increasing amounts of extracellular copper or increasing amounts of diamsar, a copper chelator. Metallothionein 1 (MT1) and MT2 mRNA levels in the cells increased in proportion to the intracellular copper concentration. The degree of stimulation was similar for both MT1 and MT2, with mRNA levels increasing approximately fourfold for a six- to eightfold increase in intracellular copper levels. In contrast, neither copper uptake nor ceruloplasmin mRNA showed any response to intracellular copper levels. Unlike the situation in the rat, there was no clear evidence for saturation of copper uptake. Incubating cells with increasing amounts of 64Cu resulted in a linear increase in the amount taken up over 2 h. The amount of 64Cu accumulated was the same in control and copper-depleted cells, which suggests that neither ceruloplasmin production nor copper uptake is regulated by intracellular copper levels. However, other possibilities, such as the chelators not being able to deplete the pool(s) responsible for the control of ceruloplasmin production or copper uptake, must also be considered.