Intracellular accumulation and retention of calcein in Ehrlich ascites tumor cells and their adriamycin-resistant strain

In this study, we observed the intracellular accumulation and retention of calcein in Ehrlich ascites tumor cells (wild type EAT cells) and their adriamycin (ADR)-resistant strain to further study the mechanisms of ADR accumulation. In the wild type EAT cells, intracellular accumulation of calcein increased rapidly, but it was not incorporated into the cells in the ADR-resistant strain. This suggests that the efflux system or the inhibition system of influx, which does not exist in the wild type EAT cells, involves in the ADR- resistant strain. Calcein incorporated into the cells was effluxed from the cells in both strains at almost the same rate. This suggests that the both strains may use a similar efflux system agaimt calcein. P-gp extrudes calcein-AM directly from the cell membrane, but not calcein. Calcein is effluxed by multidrug resistant protein (MRP) or multispecific organic anion transporter (MOAT). Therefore, the mechanism, which extrudes calcein of both strains, may be the other efflux system included MRP or MOAT apart from P-gp. In the same medium condition as treating in the calcein efflux experiments, about 20% amount of ADR incorporated into the cells was effluxed in the ADR-resistant cells, but not in the wild type cells. Since the efflux rates in the ADR differed from those in calcein in the same medium condidon, the mechanism of the ADR efflux might differ from that of calcein efflux in the ADR-resistant strain.