Copper Uptake by Nongastrointestinal Vertebrate Cells

Abstract

Apart from the intestinal mucosa, most of the work on copper uptake by internal eucaryotic cells has been done with hepatocytes, especially those of the rat. Beginning with studies on liver slices incubated in Krebs—Ringer solution with ⁶⁴Cu-labeled Cu(II) citrate, it was shown by Saltman et al. (1959) that copper uptake obeyed saturation kinetics. Subsequent studies by Harris and Sass-Kortsak (1967), in which 0.1 volume of dialyzed serum was added to the Krebs—Ringer buffer, were consistent with a first-order process but showed that the addition of amino acids in a mixture containing 63 µM histidine (9.7 mg/liter), 71 µM cysteine (8.6), and 370 µM threonine (44), as well as most other amino acids in approximately physiological amounts, stimulated uptake two- to three-fold at Cu concentrations from 6.4 to 200 µM (0.1–5 mg/ml). This was also observed by Neumann and Silverberg (1966), who reported that histidine (4–12 µM) stimulated uptake of ⁶⁴Cu (10 µM) by rat liver or kidney slices (or by Ehrlich ascites tumor cells) when incubated in a Krebs—Ringer medium containing 4% albumin. Harris and Sass-Kortsak (1967) showed that there was the same degree of uptake (and stimulation of uptake) by amino acids at two different albumin concentrations, corresponding to about 0.3 and 1.5 g/dl. Also, the absence of an oxygen atmosphere had little effect on copper uptake recorded in the absence of amino acids but profoundly inhibited (in fact, more or less abolished) the stimulatory effect of the added amino acids. In contrast, 2,4-dinitrophenol (1 × 10⁻⁴−1.8 × 10⁻⁴ M) had no effect on uptake measured in the absence or presence of extra amino acids, implying that the oxygen dependency of the amino acid stimulatory effect (if indeed it is reproducible) is not mediated by intracellular ATP availability.