Kinetics of Cu(II) transport and accumulation by hepatocytes from copper-deficient mice and the brindled mouse model of Menkes disease

The kinetics of 64Cu(II) uptake, efflux and net accumulation were examined with hepatocytes isolated from hemizygous and heterozygous brindled mice to determine the basis for the low hepatic copper levels in these mice. Initial rate data (0.5 min) for 64Cu(II) uptake showed no significant differences between the normal and mutant hepatocytes for the Km and Vmax parameters for copper uptake. The rate and total efflux of 64Cu from preloaded cells were also normal for both the hemizygous and heterozygous brindled hepatocytes. Normal and mutant hepatocytes exhibited an overshoot in net 64Cu(II) uptake when cells were incubated continuously with 64Cu(II) for 6 h. Maximal intracellular levels were attained at 1.5 to 2.5 h before a lower steady state was achieved by approximately 3 h. The mutant hepatocytes were also normal with respect to the time-delayed efflux process responsible for the overshoot in terms of 64Cu lost/min/mg of protein. However, both the hemizygous and heterozygous hepatocytes showed approximately 25% less than normal maximal copper accumulation. This accounted for the approximately 25% lower copper levels at steady state and also equaled the Cu deficiency in the resting whole livers. The impaired Cu accumulation characteristic is not a general property of Cu-deficient hepatocytes because nutritionally Cu-deficient hepatocytes exhibited higher than normal net 64Cu accumulation. The effect was Cu-specific since 65Zn(II) accumulation was normal with the mutant hepatocytes. The results are consistent with expression of the primary defect at the cellular level in the liver in the mouse mutants, and by inference, Menkes disease.