Active transport of lead by human red blood cells

Human red cells suspended in lead-citrate buffers (2.6 microM Pb2+) take up much less Pb than predicted from studies of equilibrium binding of Pb to haemolysates. Pb uptake is increased by ATP depletion, or by loading at 0 degrees C. Tracer studies with 203Pb indicate that the low uptake at 37 degrees C in the presence of substrate is not due to membrane impermeability to Pb. Cold-loaded cells extrude Pb against a concentration gradient at 37 degrees C when glucose is present. These results suggest that the cellular loading of Pb is dependent on the balance between an inward leak and an outward pump. The extrusion of Pb from the cells is possibly brought by the Ca pump.