THE INFLUENCE OF EXTERNAL SURFACE-POTENTIAL AND TRANSMEMBRANE POTENTIAL ON THE PASSIVE TRANSBILAYER MOVEMENT OF PHOSPHOLIPIDS IN THE RED-BLOOD-CELL MEMBRANE

The passive transbilayer movement of spin-labelled analogues of phosph atidyl-choline (PC), phosphatidyl-ethanolamine (PE), and phosphatidyl- serine (PS) in red blood cell membranes was investigated at physiologi cal and low ionic strength of the extracellular solution. Passive tran sbilayer movement of aminophospholipids PS and PE was measured in ATP- depleted cells. To discriminate between a possible surface potential a nd a transmembrane potential effect, NaCl in physiological ionic stren gth solution was replaced either by sucrose or by Na-tartrate (constan t osmolarity). Neither in sucrose (low ionic strength) nor in Na-tartr ate media a significant change of the translocation rate of the phosph olipids was observed. From these results it call be concluded that cha nges of the external surface potential as well as of the transmembrane potential do not affect the passive transbilayer movement of phosphol ipids in human red blood cells.