Mercury Uptake by Primary Cultures of Rat Renal Cortical Epithelial Cells.II. Effects of pH, Halide Ions, and Alkali Metal Ions

Abstract

The effects of pH, halide ions, and alkali metal ions on the uptake of inorganic mercury (Hg) were investigated in confluent primary cultures of rat renal cortical epithelial cells. The cells were incubated with 1 μM Hg in phosphate buffer at pH 5.5, 6.4, or 7.4 for 30 min at 37 °C. Incubation of cells at pH 5.5 resulted in a 22% increase in total Hg accumulation over those cells that were incubated at pH 7.4. Almost all of this increase was accounted for in the membrane fraction. In contrast, there was a 33% reduction in internalized Hg in cells incubated at pH 5.5. This may be explained by the conversion of hydroxide forms of Hg (Hg(OH)Cl and Hg(OH) 2) to the chloride forms (HgCl 2, HgCl − 3, and HgCl 2− 4) at a lower pH (decreased OH −) condition. In the presence of halide ions, the cells internalized Hg in the relative order of affinity of the halide ions for Hg 2+ (i.e., F − < Cl − < Br − < I −). Br − and I − resulted in a 67 and 142% increase in internalized Hg over that by Cl −. The relatively high membrane binding and internalization of Hg in the presence of Br − and I − was possibly due to the formation of highly lipophilic complexes of Hg (i.e., HgBr 2 and HgI 2). The replacement of NaCl in the incubation medium by KCl caused a 36% decrease in internalized Hg. LiCl had a similar effect on the internalization of Hg. The above results suggest that in rat renal proximal tubules Hg uptake involves Na +-and H +-dependent mechanisms.