Further findings on the mechanism of cadmium uptake by intestinal mucosal cells (step 1 of Cd absorption).

This work confirms and extends earlier studies on the mechanism of Cd uptake (step 1 of absorption) by the jejunal mucosa of the rat. The Q10 for step 1A, the binding of Cd to the membrane, approximates 1.0. Internalization of bound Cd (step 1B) exhibits a constant Q10 of 1.4 between 0 and 37 degrees C, providing no evidence for a phase shift in the membrane in that range. Chelators which compete for Cd with the membranes thereby inhibit step 1. Membrane-bound Cd behaves kinetically as a single pool, even though only 1/3 participates in step 1B. Binding does not involve reactive -SH groups. Fractional uptake of 5 microM 109Cd is equally depressed by 250 microM Cd or Zn; the non-specific apparent saturation of Cd uptake can be explained by charge neutralization on the membrane, and does not require postulation of Cd carriers. These findings support the proposed model of jejunal Cd uptake.