Nanomolar concentrations of Cd2+ inhibit Ca2+ transport systems in plasma membranes and intracellular Ca2+ stores in intestinal epithelium.

The interactions of Cd2+ with active Ca2+ transport systems in rat intestinal epithelial cells have been investigated. ATP-driven Ca2+ transport in basolateral plasma membrane vesicles was inhibited by Cd2+ with an I50 value of 1.6 nM free Cd2+ at 1 microM free Ca2+, using EGTA and HEEDTA to buffer Ca2+ and Cd2+ concentrations, respectively. The inhibition was competitive in nature since the Km value of Ca2+ increased with increasing Cd2+ concentrations while the Vmax remained constant. Cd2+ had similar effects on ATP-dependent Ca2+ uptake by permeabilized enterocytes, indicating that non-mitochondrial and mitochondrial Ca2+ stores are also inhibited by nanomolar concentrations of Cd2+. We conclude that ATP-driven Ca2+ transport systems are the most sensitive elements so far reported in Cd2+ intoxication.