Inhibitory effect of cadmium on vitamin D-stimulated calcium transport in rat duodenum in vitro.

In vitro effect of cadmium on vitamin D-stimulated calcium transport in the rat was studied using the everted gut sac technique. Calcium transport was significantly inhibited by the addition of cadmium to the mucosal incubation medium. Furthermore, the kinetic analysis of inhibitory effect of cadmium on calcium transport revealed that the type of inhibition was competitive. The apparent "Km" and "Vmax" value for calcium was 1.0 mM, and 2.86 mumoles ml-1.hr-1, respectively. An apparent "Ki" for cadmium was 0.02 mM.