Effect of Pb2+ on Friend leukemia cells during erythroid maturation

The effect of different concentrations of Pb²⁺ on the growth rate and on the percentage of hemoglobin-synthesizing cells of Friend leukemia cells was determined. Pb²⁺ had a higher inhibitory effect on the growth and on the final percentage of hemoglobin-synthesizing cells when cultures were induced to erythroid differentiation by either dimethyl sulfoxide or hexamethylenebisacetamyde (HMBA) as compared with uninduced cultures. The increased sensitivity to Pb²⁺ of cultures containing either dimethyl sulfoxide or (HMBA) appeared to be correlated with the differentiation process triggered by these two substances, since the increased sensitivity was not observed with a Friend leukemia cells variant which did not differentiate in the presence of any inducer. The effect of Pb²⁺ on the activities of δ-aminolevulinic acid (ALA) dehydratase and URO synthetase, two enzymes involved in heme synthesis, was also determined. Induced cells continuously grown in the presence of Pb²⁺ up to 72 hr postinduction were not affected in URO synthetase activity, whereas the activity of ALA dehydratase was decreased as compared with induced cultures grown without lead. By 96 and 120 hr postinduction an increase in URO synthetase activity and a decreased inhibition of ALA dehydratase activity were observed. The inhibitory effect of Pb²⁺ on the growth rate of induced cells was much higher when cultures were treated during the first 24 hr of growth than it was when Pb²⁺ was added during the second 24 hr. In uninduced cultures the same low level of inhibition was observed following treatment during either 24-hr period. Cell agglutinability by plant lectins was also inhibited in induced cultures by the presence of Pb²⁺ during cellular growth.