COMPARATIVE-STUDIES OF CADMIUM AND MERCURY ACCUMULATION BY LLC-PK1 CELLS - EFFECTS OF PH ON UPTAKE AND EFFLUX

Effects of pH on internalization, membrane-binding and efflux of Cd we re investigated in LLC-PK1 cells and these effects were compared with those of inorganic mercury (Hg). The cells cultured on monolayers were incubated for 30 min in phosphate buffer at pH 5.5, 6.4 or 7.4 contai ning 1 mu M Cd or Hg. After the incubation, the cells were washed with phosphate buffered saline (PBS) or PBS containing chelating agent (EG TA or BAL) to remove membrane-bound Cd or Hg. The decrease in pH signi ficantly decreased Cd concentration in the cells washed with PBS and w ith PBS-EGTA, and apparently increased the efflux of Cd from the cells . Similar changes were found in Hg concentration in the cells washed w ith PBS-BAL and Hg efflux from the cells, but these changes in Hg were less significant than those in Cd, respectively. The decrease in pH i ncreased Hg concentration in the cells washed with PBS, unlike that of Cd. These results suggest that a decrease in pH decreases the interna lized Cd as a result of the decrease in membrane-bound Cd and the incr ease in Cd efflux. The decrease in pH also appears to decrease the int ernalized Hg by increasing Hg efflux and to increase the membrane-boun d Hg.