Uptake of lead by human red blood cells and intracellular distribution

Lead added to plasma was rapidly incorporated into suspended human red blood cells at 37 degrees C. The rate of lead uptake into the cells reached a maximum of 35 micrograms (0.17 mumole)/10(10) cells/h. The rate of lead uptake with resealed ghosts was comparable to that of intact cells. These findings indicate that the transport of lead across the erythrocyte membrane is, energy-independent, carrier-mediated passive transport, which confirms the conclusion of Simons. On the other hand, little release of incorporated lead from the cells in lead-free plasma was observed. Some 98% of intracellular lead was in cytoplasm, mostly in protein-bound form, and only 2% was in the membrane fraction. When red blood cells were incubated in plasma containing lead at about 10 mg/dl concentration for 24 hours at 37 degrees C, no progressive accumulation of lead and protein in the membrane fraction was observed. Thus, lead-protein complexes in cytosol are unlikely to associate with membranes. Human haemoglobin had forty-five binding sites for lead with the dissociation constant of 0.5 x 10(-6) M. The binding of lead to oxyhaemoglobin did not show any effect on the iron atom in the heme.