The effects of K+-depolarization medium, chelating agents and thiol groups on cadmium uptake and efflux in the guinea-pig taenia coli

Cadmium uptake by taenia coli was dose-dependent, achieving equilibrium after approximately 60 min of incubation. The SH-blocker, N-ethylmaleimide inhibited cadmium uptake. When muscles were washed with normal medium or that containing 0.5 mM EDTA following 0.5 mM Cd2+ treatment for 60 min, the tissue cadmium concentration reached equilibrium levels after 60 min and approximately 43 or 27% of the initial tissue cadmium concentration was retained, respectively. Both glutathione and dithiothreitol also increased cadmium efflux. However the contractions of glycerinated taenia coli caused by Ca2+ and Mg-ATP, completely returned to control values after washing with 0.5 mM EDTA medium following 0.5 mM Cd2+ treatment for 60 min, suggesting that EDTA seems to exert intracellular effects in glycerinated taenia coli. These results suggest that SH-dependent mechanisms in cadmium uptake play a role in intact taenia coli. In addition, in intact taenia coli, Cd2+ are accumulated in intracellular compartments which EDTA cannot reach and may exert an inhibitory action on internal sites in the cells.