MERCURY UPTAKE BY LLC-PK1 CELLS - DEPENDENCE ON TEMPERATURE AND MEMBRANE-POTENTIAL

The purpose of this study was to investigate the mechanism of inorgani c mercury (Hg) uptake in LLC-PK1 cells, a renal tubular epithelial cel l line, and to compare the results with those reported previously by u s in rat renal cortical epithelial (RCE) cells in primary culture. The LLC-PK1 cells were cultured for 3-12 days, incubated with 1 mu M HgCl 2 in Hanks' balanced salt solution at 4 or 37 degrees C for 30 min, an d washed with phosphate-buffered saline containing BAL to remove the c ell membrane-bound Hg. The uptake of Hg was higher in nonconfluent cul tures than in confluent cultures and higher at 37 than at 4 degrees C. In confluent culture (Day 8) Hg uptake at 4 degrees C was only 27% of that at 37 degrees C. The initial accumulation of Hg (5 min) from dif ferent concentrations of HgCl2 (0.5-50 mu M) was linear and did not sh ow a tendency toward saturation, suggesting that a carrier-mediated pr ocess was not involved. Pretreatment of cells with 10 mu M FCCP, a met abolic inhibitor and a proton ionophore, 0.5 mM DIDS, an anion transpo rt inhibitor, or 0.5 mM ouabain, a Na+/K+-ATPase inhibitor, resulted i n 72, 60, and 57% reduction in Hg uptake, respectively. Furthermore, r eplacement of 137 mM NaCl in the incubation medium with 137 mM KCI or LiCl or 274 mM mannitol caused 30, 45, and 87% reduction in Hg uptake, respectively. These results suggest that in LLC-PK1 cells, as in RCE cells, Hg uptake is inversely related to cell density and is influence d by membrane fluidity, membrane potential, and HCO3-/Cl- transporter. (C) 1997 Academic Press.