The funetional fluorescent dye efflux assays are used in the study of the multidrug resistence of the malignant cella to the cytotoxic droga which is caused by the overexpression of P-glycoprotein (P-gp) or another membrane transport system - a multidrug resistence related protein (MRP). P-glycoprotein and a multidrug resistence related protein are involved in the efflux of cytotoxic drngs out of the cell and are responsible for the resistence. Fluorescent dye efflux mediated by these proteins could be evaluated by the flow cytometry. This test seems to be an optimal approach to study the multidrug resistence. With help of the speciflc inhibitors such as verapamil and cyclosporine A, the functional capacity of these proteins and the possibility to overcome the multiresistant phenotype cen be revealed. The cell line K562 with transfected P-glycoprotein Bene serves as a model system for the studying of the transport funetion with the ose of the fluorescent substrates and P-glycoprotein inhibitors.

        Key words: Multidrug resistence - Cytotoxic droga - flow cytometry - Cell line K6(i2 - Fluorescent substrates