Zinc exchange by blood cells in nearly physiologic standard conditions
Abstract
Determination of zinc concentrations in white blood cells has been used to establish zinc deficiency. During pathological conditions changes in zinc concentrations in these blood cells were observed. However, these investigations were hampered by the low amount of zinc in this form per mL blood. Earlier we demonstrated that, in the case of zinc deficiency, the uptake of zinc was increased, using the in vitro exchange of zinc by the various blood cells with extracellular zinc labeled with65Zn in fairly physiologic conditions. In case of inflammation, no increase in zinc uptake by erythrocytes was seen, indicating that this method probably can be used to differentiate real from apparent zinc deficiency. Only during the first days of the inflammatory process, probably representing the redistribution phase during which zinc moves from the serum to the liver, a small increase in in vitro zinc uptake was seen in mononuclear cells (MNC) and polymorphonuclear cells (PMNC).
Earlier papers raised some questions; e.g., is the uptake part of an exchange process and can the efflux of zinc by the cells be measured by the same method; what is the influence of time on the process of zinc uptake; what is the magnitude of the uptake of zinc by the cells compared to the zinc concentration in the cells; and, what is the influence of temperature on the uptake of zinc?
In the present study, the influence of incubation time and temperature on the uptake of zinc by human and rat blood cells and on the release of zinc by rat blood cells was studied. At least three phases of uptake of zinc in the various cells were found by varying the incubation time—a fast phase during the first half hour, probably caused by an aspecific binding of zinc on or in the cell membrane; a second fast uptake between 60–330 min, probably caused by an influx of zinc in the cell as part of the exchange process of zinc; and a slow third phase after 5.5 h, in which probably the in- and efflux of the rapidly exchangeable intracellular pool is more or less equilibrated. For mononuclear cells, polymorphonuclear cells, and erythrocytes of rats, the rapidly exchangeable intracellular pool is 40%, 53%, and 10%, respectively, of the total zinc content of the cells. This study is also performed in human cells; in human cells the exchangeable pool of mononuclear cells and erythrocytes is 17 and 3.5% of the total zinc content of the cells, respectively. The efflux of zinc by blood cells can be measured by the same method. Both the uptake and the loss of zinc by blood cells of rats were compared and are of the same magnitude, indicating that the in vitro uptake of zinc described elsewhere is part of an exchange process. Increasing temperature during incubation procedures results in an increase of zinc uptake by human blood cells, even at high temperatures of 41°C, although there are gradual differences between the various blood cells. Both the in- and efflux of zinc by blood cells are very small at 4°C.
Index Entries
Zinc rats humans blood cells temperature uptake efflux exchangeAbbreviations
- GPB
glucose phosphate buffer
- MNC
mononuclear cells
- PMNC
polymorphonuclear cells
- ip
intraperitoneally
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