Mercury remains a serious environmental and occupational hazard, ranging from industrial waste to dental amalgams. The kidney is one of the target organs for the toxic effects of mercury, presumably because the kidney of mercury, accumulates more inorganic mercury than any other organ. The kidney also serves as a major route for the excretion of mercury, but very little is known about the mechanisms involved in the renal tubular transport, accumulation and toxicity of inorganic mercury. Thus very little is known about the mechanisms involved in the urinary excretion of the metal. The main thrust of this grant is to characterize the renal transport, accumulation, toxicity, and metabolism of inorganic mercury.
The aims of this grant will be carried out using both in vivo and in vitro techniques. One of the principal techniques we will use is the isolated perfused rabbit renal tubule. This technique will allow us to determine simultaneously the renal tubular uptake and transepithelial lumen-to-bath and bath-to-lumen transport of mercury in various isolated segments of the nephron. We will study the transport, accumulation and toxicity of mercury in isolated segments of the proximal tubule (S1, S2, and S3), medullary thick limb of Henle's loop and cortical collecting ducts. These studies will determine if there is axial heterogeneity for transport and accumulation of mercury along the nephron. The studies on the distal segments are important because very little is known about the handling of mercury beyond the proximal tubule. Since inorganic mercury binds avidly to free sulfhydryl groups, we will also examine the effects of compounds that contain sulfhydryl groups on these processes. In order to determine if extracellular cysteine, glutathione and albumin participate in the accumulation and transport of mercury in segments of the nephron, we will use both radiolabelled inorganic mercury (203Hg) and radiolabelled cysteine and glutathione (35S) and albumin (125I) both in vivo and in vitro. The intrarenal localization of mercury and ligand will be determIned for zones of the kidney, while the transport and accumulation of the ligand and mercury will be studied in isolated perfused segments of the nephron. The accumulation and transport of mercury will also be studied when mercury is in an ultrafiltrate of rabbit plasma and when it is complexed with metallothionein. Furthermore, the transport, accumulation and toxicity of mercury will be evaluated when renal intracellular glutathione is depleted and when intracellular synthesis of metallothionein is stimulated. We will also attempt to localize mercury in subcellular fractions of renal tissue from rabbits treated with mercury and the various ligands. In addition, an autometallographic technique will be combined with the isolated perfused tubular technique in an attempt to determine the intracellular localization and accumulated mercury. We will also determine if the metal chelators DMPS and DMSA promote the removal of mercury from various isolated perfused nephron segments when applied to the luminal or basolateral membrane. In summary, from this study we should be able to determine the role of endocytosis and carrier mediated transport in the renal transport and accumulation of free and bound inorganic mercury. Furthermore, this study should provide some insights into the factors influencing the toxicity of mercury in renal epithelia.
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