title: The role of anion transport in the passive movement of lead across the human red cell membrane.
abstract: Passive Pb transport across the red cell membrane has been studied by measuring Pb uptake from Pb-buffered solutions into resealed ghosts containing EGTA. 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) greater than phloretin greater than furosemide and bumetanide. Ouabain and cytochalasin B are ineffective. This implicates the anion-exchange mechanism in Pb uptake. 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. Pb transport depends upon the presence of a second anion. In the presence of HCO3-, the rate is stimulated in the order ClO4- less than NO3- and CH3CO2- less than F- less than Cl- less than Br- less than I-. The temperature dependence of Pb uptake is similar to that of HCO3-(-)Cl- exchange. 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. 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.
mesh_terms: D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid / Q000031:analogs & derivatives*; D012856:4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D000838:Anions / Q000378:metabolism; D001639:Bicarbonates / Q000494:pharmacology; D001692:Biological Transport / Q000187:drug effects; D004232:Diuretics / Q000494:pharmacology; D004910:Erythrocyte Membrane / Q000378:metabolism*; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007854:Lead / Q000097:blood* / Q000494:pharmacology; D008564:Membrane Potentials; D010693:Phloretin / Q000494:pharmacology; D013449:Sulfonamides
chemical_list: D000838:Anions; D001639:Bicarbonates; D004232:Diuretics; D013449:Sulfonamides; D012856:4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic Acid; D007854:Lead; C018564:dihydro-DIDS; D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid; D010693:Phloretin