The uptake of the Cd-metallothionein complex (CdMT) into LLC-PK
1 cells was investigated and compared with that of CdCl
2. The cells were incubated at 37°C for up to 45 min with 1 μM Cd, as either CdMT or CdCl
2 at pH 5.5, 6.4, or 7.4. Under all the experimental conditions described below, the accumulation of Cd from CdMT was markedly lower than that from CdCl
2. Cd accumulation at pH 7.4 from CdMT increased linearly with the time of incubation, whereas Cd accumulation from CdCl
2 was saturable. Metabolic inhibitors, 2, 4-dinitrophenol(DNP) and carbonylcyanide p-(trifluoromethoxy)-phenylhydrazone (FCCP), and incubation at low temperature significantly decreased Cd accumulation from both Cd compounds. Coincubation with 30 μM ZnCl
2, an antagonist of CdCl
2 uptake, slightly decreased Cd accumulation from CdMT, but it markedly decreased that from CdCl
2. Cd accumulation from CdMT at pH 5.5 was significantly higher than at pH 6.4 or 7.4, whereas Cd accumulation from CdCl
2 at pH 5.5 and 6.4 was significantly lower than at pH 7.4. Although Cd accumulation from CdCl
2 at pH 7.4 was significantly decreased by coincubation with 100 μM cysteine or glutathione (GSH), this decrease was not observed at pH 5.5 or 6.4. A small amount of Cd was removed, by the chelating agent EGTA, from the cell membranes after incubation with CdMT at pH 6.4 and 7.4, whereas a considerable amount of Cd was removed by EGTA after incubation with CdMT at pH 5.5 and with CdCl
2 at three pHs. It appears that the CdMT complex is taken up into LLC-PK
1 cells partially via an energy-dependent process, and the increase in Cd accumulation at low pH is due to the liberation of Cd. High stability and molecular size of the CdMT complex explains why it is not taken up readily into LLC-PK
1 cells.
抄録全体を表示