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 phosphatidyl-choline (PC), phosphatidyl-ethanolamine (PE), and phosphatidyl-serine (PS) in red blood cell membranes was investigated at physiological and low ionic strength of the extracellular solution. Passive transbilayer movement of aminophospholipids PS and PE was measured in ATP-depleted cells. To discriminate between a possible surface potential and a transmembrane potential effect, NaCl in physiological ionic strength solution was replaced either by sucrose or by Na-tartrate (constant osmolarity). Neither in sucrose (low ionic strength) nor in Na-tartrate media a significant change of the translocation rate of the phospholipids was observed. From these results it call be concluded that changes of the external surface potential as well as of the transmembrane potential do not affect the passive transbilayer movement of phospholipids in human red blood cells.