METAL TRANSPORT IN CELLS - CADMIUM UPTAKE BY RAT HEPATOCYTES AND RENAL CORTICAL EPITHELIAL-CELLS

The toxic metals appear to use the transport pathways that exist for b iologically essential metals. In this regard interactions between the toxic and essential metals are possible. This report summarizes recent findings on the transport of cadmium in rat hepatocytes and renal cor tical epithelial cells in the presence or absence of certain essential metals. The transport of cadmium in hepatocytes does not require ener gy and, therefore, is not an active process. It occurs primarily (80%) by temperature-sensitive processes, i.e., ion channels and carriers, that involve interaction with sulfhydryl groups. These processes appar ently exist for the transport of essential metals like copper, zinc an d calcium. The remaining 20% of the cadmium in hepatocytes is transpor ted via a temperature-insensitive process, possibly by diffusion. In c omparison with the hepatocytes, a smaller fraction (30%) of the cadmiu m transport through the basolateral membrane and none from the apical membrane of the renal cortical epithelial cells is temperature-sensiti ve. Total accumulation through the basolateral membrane is about twice that through the apical membrane. A majority of the cadmium transport in the renal cells is by diffusion. As in hepatocytes, copper, zinc a nd mercury antagonize cadmium transport through the apical membranes o f the renal cells. The relative antagonism by copper is the same (25%) ; however, the antagonism by zinc (16%) and mercury (10%) is 4- to 6-f old lower than in hepatocytes. II appears that the relative contributi on of various transport pathways available for cadmium uptake is diffe rent in each cell type and apparently depends on the morphological and functional differences between the cell membranes.