Calcium-cadmium interaction on L-threonine intestinal transport

Cadmium is a highly toxic metal that can damage a number of organs including the gastrointestinal tract. It has been shown that cadmium partially reduces L-threonine intestinal absorption probably by binding to membrane proteins which pertain to active transport systems or are functionally related to them. Calcium, however, is an essential element in a wide variety of cellular activities. The aim of the present work was to study whether the inhibitory cadmium effect on L-threonine absorption across rabbit jejunum could be modified by calcium. In media with Ca2+, cadmium significantly reduces the L-threonine absorption. In Ca(2+)-free media, where calcium chloride was omitted and replaced isotonically with choline chloride, this amino acid transport was not modified by cadmium but it was inhibited when calcium chloride was replaced isotonically with magnesium chloride. Verapamil (blocking mainly Ca2+ transport) did not modify the inhibitory effect of cadmium on L-threonine transport. When A 23187 (Ca2+ specific ionophore) was added in media with/without Ca2+, cadmium produced no change on L-threonine transport. These results suggest that calcium and cadmium could have an affinity for the same chemical groups on the enterocyte membrane. This property could affect the intestinal absorption of amino acids.