COMPARISON OF CADMIUM UPTAKES FROM APICAL AND BASOLATERAL MEMBRANES OF LLC-PK1 CELLS

Cadmium (Cd) uptake from the apical and basolateral membranes was inve stigated in LLC-PK1 cells grown as a monolayer on a permeable membrane . The cells were incubated at 37 degrees C for 1 hr with 1 mu M CdCl2 from either the apical or the basolateral side. The accumulation of Cd from the apical side was 23% higher than that from the basolateral si de, However, the translocation of Cd from the apical to the basolatera l side and vice versa were similar. Cytotoxicity, as evaluated by tran sepithelial electrical resistance (TER), was undetectable at 1 mu M Cd concentration. The preincubation of cells with carbonylcyanide p-(tri fluoromethoxy)-phenylhydrazone (a metabolic inhibitor) and ouabain (a Na+/K+-ATPase inhibitor) or coincubation with Cd and 2,4-dinitrophenol (a metabolic inhibitor) decreased both the accumulation (16-24%) and the translocation of Cd (22-25%) from the apical side, but not from th e basolateral side, Incubation of cells with 50 and 75 mu M CdCl2 for 1 hr resulted in 52-112% higher accumulation and translocation of Cd f rom the basolateral than from the apical side, The TER decreased at hi gh Cd concentrations, suggesting that Cd concentrations of 10 mu M and higher were cytotoxic, It is concluded that uptake of Cd from both th e apical and the basolateral membranes represents passive diffusion, A dditionally, under nontoxic conditions, about 20% of the Cd taken up a t the apical membrane reflects carrier-mediated transport involving so dium ion- and energy-dependent processes; this accounts for higher acc umulation through the apical membrane. (C) 1996 Academic Press, Inc.