Uptake of lead by human erythrocytes in vitro

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Abstract
A study is described of the uptake of Pb in vitro by human erythrocytes, including experiments on the form of Pb in plasma and the kinetics of lead-binding. Pb appears to exist in plasma as a peptized lead phosphate sol, which is rapidly aggregated in a 2d-order reaction to particulate form on the surface of the erythrocytes. More than 95% of small quantities of added Pb are rapidly attached to the cells. No competitive inhibition of uptake of Pb was observed with any of a number of potential competitors tested, including other heavy metals, Cu++, Hg++, (UO2)++ and Tl++++ ions. Chelating agents such as ethylenediaminetetraacetic acid, hexametaphosphate and glutathione remove Pb attached to erythrocytes only slowly in vitro; intracellular Pb was not withdrawn. It is suggested that the protective effect of plasma and of other solutions containing excess of phosphate is due to a charge effect on the lead phosphate sol, leading to additional negative charge on the erythrocyte.