MERCURY UPTAKE BY PRIMARY CULTURES OF RAT RENAL CORTICAL EPITHELIAL-CELLS .2. EFFECTS OF PH, HALIDE-IONS, AND ALKALI-METAL IONS

The effects of pH, halide ions, and alkali metal ions on the uptake of inorganic mercury (Hg) were investigated in confluent primary culture s of rat renal cortical epithelial cells. The cells were incubated wit h 1 mu M Hg in phosphate buffer at pH 5.5, 6.4, or 7.4 for 30 min at 3 7 degrees 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 fract ion. In contrast, there was a 33% reduction in internalized Hg in cell s incubated at pH 5.5. This may be explained by the conversion of hydr oxide forms of Hg (Hg(OH)Cl and Hg(OH)(2)) to the chloride forms (HgCl 2, HgCl3-, and HgCl42-) at a lower pH (decreased OH-) condition. In th e presence of halide ions, the cells internalized Hg in the relative o rder of affinity of the halide ions for Hg2+ (i.e., F- < Cl- < Br- < I -). Br- and I- resulted in a 67 and 142% increase in internalized Hg o ver that by Cl-. The relatively high membrane binding and internalizat ion of Hg in the presence of Br- and I- was possibly due to the format ion of highly lipophilic complexes of Hg (i.e., HgBr2 and HgI2). The r eplacement of NaCl in the incubation medium by KCl caused a 36% decrea se in internalized Hg. LiCl had a similar effect on the internalizatio n of Hg. The above results suggest that in rat renal proximal tubules Hg uptake involves Na+-and H+-dependent mechanisms. (C) 1995 Academic Press, lnc.