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

-(trimethylamino)phenyl]-6-phenylhexa-1,3,5-triene (TMA-DPH), a membra ne fluorescence probe, interacts with living cells by instantaneous pa rtition 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 consti tutive intracellular traffic and behaves as a monitor for endocytosis. Using this tool on L929 synchronized cells, we showed that the endocy tosis levels after 30 min uptake of the probe increased from G1 to mit osis, when they abruptly decreased. The cell surface remained constant throughout the cell cycle, except at the beginning of mitosis when it almost doubled.