The mechanism and control of human erythrocyte zinc uptake

The increasing awareness of the importance of the divalent cation zinc in normal and pathologic cell functions has prompted our investigations into the mechanism and control of human erythrocyte zinc uptake. The albumin in blood plasma appears to be the main zinc binding moiety, effectively limiting zinc availability ot the red cell. In non-protein and non-phosphate-containing buffers (i.e., bicarbonate or Tris buffer) red cells sequester more than 90% of the extracellular zinc within 10--15 minutes at a rate more than 250 times faster than zink uptake by cells in plasma. In an albumin-containing media, the influx on red blood cell zinc is lightly temperature sensitive (decreased) between 37 degrees C and 25 degrees C, whereas with cells in bicarbonate buffer alone temperature sensitivity does not begin until below 25 degrees C. Over the physiological range, pH variation has a minimal effect on zinc uptake regardless of the media employed. Finally, once associated with the red cell zinc tends to remain, with a zinc efflux less than 2% of influx. We conclude that human erythrocytes are highly permeable to zinc, with the rate and amount of zinc taken up controlled primarily by the zinc binding characteristics of the media in which the cells are suspended.