The role of anion transport in the passive movement of lead across the human red cell membrane.

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Abstract
1. Passive Pb transport across the red cell membrane has been studied by measuring Pb uptake from Pb-buffered solutions into resealed ghosts containing EGTA. 2. Over 90% of Pb uptake occurs by a pathway which is inhibited by drugs which block anion transport. The order of effectiveness is 4,4''-diisothiocyanostilbene-2,2''-disulphonic acid (DIDS) and 4-acetamido-4''-isothiocyanostilbene-2,2''-disulphonic acid (SITS) > phloretin > furosemide and bumetanide. Ouabain and cytochalasin B are ineffective. This implicates the anion-exchange mechanism in Pb uptake. 3. The rate of Pb uptake by this route is directly proportional to external Pb2+ and HCO3- concentrations, and inversely proportional to the H+ concentration. These findings suggest that Pb transport depends on the formation of PbCO3 in solution. 4. Pb transport depends upon the presence of a second anion. In the presence of HCO3-, the rate is stimulated in the order ClO4- < NO3- and CH3CO2- < F- < Cl- < Br- < I-. 5. The temperature dependence of Pb uptake is similar to that of HCO3--Cl- exchange. 6. Changes in membrane potential appear to influence Pb transport. The effects are small and somewhat variable, but in general a negative internal potential accelerates uptake and reduces exit. A positive internal potential reduces uptake and accelerates exit. 7. These results suggest that Pb is transported on the anion exchanger. Exchange of PbCO3 for a monovalent anion best fits the experimental data, although transport of a ternary PbCO3-anion- complex is a possibility.