INCREASED VESICLE ENDOCYTOSIS DUE TO AN INCREASE IN THE PLASMA-MEMBRANE PHOSPHATIDYLSERINE CONCENTRATION

Endocytosis vesiculation consists of local membrane invaginations, con tinuously generated on the plasma membrane surface of living cells. Th is vesiculation process was found to be activated in vivo by the gener ation of a transmembrane surface area asymmetry in the plasma membrane bilayer, after enhancement of transbilayer phospholipid translocation . The observed enhancement was shown to be in good quantitative agreem ent with a theoretical model of elastic equilibrium describing stabili zation of 100-nm vesicles in response to phospholipid redistribution. Very rapid dynamic vesiculation and direct re-fusion of the vesicles, both dependent on the phospholipid translocation activity, were found on a time scale of seconds. Both vesiculation and re-fusion were shown to result in a steady-state population of internal vesicles at long t ime points. The plasma membrane appears to be a dynamic structure, osc illating between two distinct curvature stales, the 10 mu m(-1) ''vesi cle'' and the 0.1 mu m(-1) ''plasma membrane'' curvature states, This dynamic behavior is discussed in terms of an elastic control of the me mbranes curvature state by the phospholipid translocation activity.