Lead accumulation by rat renal brush border membrane vesicles

Pb++ accumulation by rat renal cortical brush border membrane vesicles was evaluated by in vitro incubation with rapid filtration technique. Pb++ uptake was time- and concentration-dependent, with apparent saturation of binding sites at 100 to 200 microM (5 sec initial rate experiments). Equilibrium binding studies (60-min incubation) showed that the ratio of bound Pb++ to free Pb++ was constant at 1.25 +/- 0.07 between 0.01 to 10 microM Pb, with decreasing bound to free ratios at higher concentrations. Osmotic experiments showed that Pb++ uptake was due primarily to membrane binding rather than intravesicular accumulation. Electrochemical gradients of NaCl, KCl or protons did not increase vesicle uptake of Pb++. Incubation of vesicles with a number of amino acids did not stimulate Pb++ uptake although two (cysteine and glutathione) and the chelators EDTA or ethylene glycol bis(beta-aminoethyl ether)-N,N'-tetraacetic acid) completely blocked this process. Competition studies with a number of other metals (at 10 microM and 1 mM) showed that only Sn++ or Sn +, La , Fe++ or Fe and Cu++ produced significant reductions in Pb++ uptake whereas Mg++, Ca++, Zn++, Cd++ and Hg++ were without effect on this process. Release of 203Pb from preloaded vesicles was accelerated in the presence of either cysteine or Sn +. Prior in vivo exposure to Pb (3 mg of Pb/kg i.v.) reduced Pb uptake to 70% of that of vesicles prepared from control animals.(ABSTRACT TRUNCATED AT 250 WORDS)