Printed in U.S.A. Cadmium Inhibition of the Erythrocyte Ca2+ Pump

The effects of cadmium (Cd2+) on transmembrane Ca2+ transport and on the membrane permeability for Ca2+ were studied in human erythrocytes. The eryth rocyte Ca2+ pump is inhibited competitively by Cd2+ via interaction with the Ca2+ transport site of the car rier and not via interaction with its activator calmo dulin. The affinity of the Ca2+ pump for Cd2+ is ex tremely high (Kt = 2.0 n M Cd2+). Cd2+ (<10"4 m) does not alter the membrane permeability for Ca2+. We con clude that the pivotal mechanism in the toxic action of Cd2+ is the inhibition of Ca2+-ATPase mediated Ca2+ extrusion. As a result Cd2+ disturbs intracellular Ca2+ homeostasis and may increase cytosolic Ca2+ (Ca2+,) to toxic levels. Cadmium, reputed for its toxicity, has become widely di