The biological mechanisms underlying the difference in bioaccumulation and toxicity of organic and inorganic forms of mercury are not well understood. In this study, we examined accumulation and toxicity of organic (CH3HgCl) and inorganic (HgCl2) mercury in sea urchin (Strongylocentrotus purpuratus) embryos. We found differences in the handling of these two forms of mercury by two cellular defenses that are critical for protection from metals, multidrug resistance associated protein (MRP) activity and Glutathione-S-Transferase (GST) activity. Inhibition of either the MRP-mediated efflux activity or GST conjugation activity, significantly increases the potency of inorganic mercury, but neither treatment has any effect on the potency of organic mercury. Similarly, inhibition of MRP activity increases intracellular accumulation of inorganic mercury but has no effect on accumulation on organic mercury. Our results indicate that GST catalyzed conjugation of inorganic mercury, and subsequent efflux by MRP protects cells from this form of mercury. The inability of these two metal defense systems to recognize or eliminate organic mercury provides new insights into mercury accumulation in organisms.

Biology,Biotechnology