COMPARATIVE EVOLUTION OF ENDOCYTOSIS LEVELS AND OF THE CELL-SURFACE AREA DURING THE L929 CELL-CYCLE - A FLUORESCENCE STUDY WITH TMA-DPH

1-[4-(trimethylamino)phenyl]-6-phenylhexa-1,3,5-triene (TMA-DPH), a membrane fluorescence probe, interacts with living cells by instantaneous partition between the external medium and the plasma membrane, where it becomes fluorescent. The corresponding fluorescence intensity is then proportional to the cell surface. On the other hand, once incorporated into the plasma membrane, TMA-DPH follows this membrane in the constitutive intracellular traffic and behaves as a monitor for endocytosis. Using this tool on L929 synchronized cells, we showed that the endocytosis levels after 30 min uptake of the probe increased from G1 to mitosis, when they abruptly decreased. The cell surface remained constant throughout the cell cycle, except at the beginning of mitosis when it almost doubled.