The fusion of the liposomes containing (N-(7-nitro-2, 1, 3-benzoxadiazol-4-yl)-1 ,2-hexadecanoyl-Sn-glycero-3-labeled phosphatidylethanolamine (NBD-PE) with A549 and A549/DDP cells was performed, and the activity of the phospholipid flippase in the plasma membrane of the cells was measured by fluorescence intensity change of NBD-PE in the outer membrane. When A549 or A549/DDP cells containing NBD-PE were incubated at 371 for 0, 30, 60 and 90 min, the fluorescence intensities in the outer membrane of the cells were 0%, 1.4%, 2.9% and 7.8% for A549 cells, and0%, 10.5%, 15.5% and 18.3% for A549/DDP cells respectively, demonstrating that the phospholipid flippase was distributed in the plasma membrane of A549 cells, but its activity in the drug-resistant A549/DDP cells was much higher than that in the A549 cells. When the A549/DDP cells were incubated with a multidrug resistance reverse a-gent, verapamil, for 60 min at 37℃, the results showed that the NBD-PE in outer membrane decreased by 25.0% compared wi The fusion of the liposomes containing N- (7-nitro-2,1,3-benzoxadiazol-4-yl) -1, 2-hexadecanoyl-Sn- glycero-3-labeled phosphatidylethanolamine (NBD- / DDP cells was performed, and the activity of the phospholipid flippase in the plasma membrane of the cells was measured by fluorescence intensity change of NBD-PE in the outer membrane. When A549 or A549 / DDP cells containing NBD-PE were incubated at 371 for 0, 30, 60 and 90 min for the fluorescence intensities in the outer membrane of the cells were 0%, 1.4%, 2.9% and 7.8% for A549 cells and 0%, 10.5%, 15.5% and 18.3% for A549 / DDP cells respectively, demonstrating that the phospholipid flippase was distributed in the plasma membrane of A549 cells, but its activity in the drug-resistant A549 / DDP cells was much higher than that in A549 cells. When the A549 / DDP cells were incubated with a multidrug resistance reverse a-gent, verapamil, for 60 min at 37 ° C, the results showed that the NBD-PE in outer membrane decreased b y 25.0% compared wi