Exchanges of lead in vitro by the rabbit crystalline lens

Lead (using 203Pb as a tracer) is accumulated by rabbit lenses in vitro. This accumulation was time and concentration-dependent and could be inhibited by La3+. The results suggest that the process involves diffusion, but an interaction with anionic sites on the cell membranes may be involved. Tissue saturation concentrations of Pb were six times greater at 10(-5) M Pb as compared with 10(-6) M suggesting that the affinity of the metal ion for tissue ligands is quite low, but comparable to that in other tissues. Loss of accumulated 203Pb was slightly increased by La3+ suggesting that some binding to the plasma membrane is occurring. The thiol agent dithiothreitol considerably enhanced loss of 203Pb. Exposure of lenses to 10(-4) M Pb for 2 days resulted in an increased accumulation of sodium and loss of potassium, but lenses remained viable in 10(-5) M Pb for at least 3 days.