On the mechanism of cellular cadmium uptake.

Review of the available evidence on the mechanism of cellular Cd uptake in the rat jejunum supports the concept that this process consists of nonspecific binding to anionic sites on the membrane, followed by a temperature-dependent and rate-limiting internalization step. Because temperature-sensitive transmembrane movement of Cd can be demonstrated also in isolated brush-border vesicles and in erythrocyte ghosts, it is not likely to result from pinocytosis but may be related directly to membrane fluidity. There is no need to assume the existence of saturable Cd carriers, or competition of Cd with essential polyvalent cations for their specific transport systems. Uptake of Cd by tubular epithelium in the kidney of the intact rabbit appears to resemble that described for the jejunum, with the internalization step limiting the rate of uptake.