NA-DEPENDENT AND ENERGY-DEPENDENT TRANSPORT OF CADMIUM INTO LLC-PK1 CELLS()

Effects of sodium ions (Na+) and metabolic inhibitors on cadmium (Cd) uptake were investigated in LLC-PK1 cells derived from pig kidney unde r the nontoxic conditions of Cd. The inoculated cells became confluent on day 7 after the logarithmic growth phase. The initial uptake of Cd (1-60 mu M) by the confluent cells (day 7) was assayed. The relations hip between the Cd uptake at 37 degrees C and Cd concentration was non linear, but the relationship at 4 degrees C was linear. Subtraction of the Cd uptake at 4 degrees C from that at 37 degrees C showed a satur able uptake against the Cd concentration. By the Eadie-Hofstee analysi s of saturable uptake, K-m and V-max were 24.6 mu M and 164 pmol Cd/mg protein/min, respectively. The uptake of Cd by the cells was signific antly decreased by ouabain and the metabolic inhibitors, and by the re placement of Na+ with potassium or choline ion in the incubation mediu m. These results suggest that Cd is incorporated into the confluent LL C-PK, cells not only by simple diffusion but also by the carrier-media ted transport involved in Na+- and energy-dependent process(es).