Translocation of cadmium from cytosol to membrane fraction in cadmium-loaded red blood cells of rats

Abstract

When rat red blood cells were incubated in a cadmium (Cd)-free medium for up to 14 hr following a 1-hr treatment with 0.5 m m-CdCl 2, the incorporated Cd, which was predominantly in the cytosol at the beginning of the incubation, progressively accumulated in the membrane fraction. In parallel with the Cd-accumulation, several cytosolic proteins including haemoglobin increased in the membrane fraction, resulting in an increase in the protein to phospholipid ratio of the membrane fraction. The membrane fraction was solubilized with sodium deoxycholate and analysed by gel-filtration chromatography. Cd was detected in the high-molecular-weight fraction containing membrane proteins at the beginning of incubation, and the Cd content of this fraction did not alter appreciably during the incubation. On the other hand, Cd in the low-molecular-weight fraction, where haemoglobin is most abundant, increased progressively during the incubation. The Cd-binding capacity of proteins in the membrane fraction was assessed by 109Cd-autoradiography using the western blotting technique. In addition to membrane proteins, haemoglobin and other cytosolic proteins, which increased in the membrane fraction during the incubation, exhibited a significant ability to bind Cd. These results indicate that Cd, once incorporated into red cell cytosol, progressively accumulates in the membrane fraction together with cytosolic proteins with Cd-binding capacity. This accumulation of Cd-cytosolic proteins may affect the membrane properties of red blood cells.