INFLUENCE OF PH ON PHOSPHOLIPID REDISTRIBUTION IN HUMAN ERYTHROCYTE-MEMBRANE

The influence of the suspension pH (pH(o)) on the transmembrane mobili ty of spin labeled phospholipid analogues in the human red blood cell was investigated, The passive transverse diffusion of spin-labeled pho spholipid analogues was independent of pH(o) in the investigated range (5.8 to 8.5). However, upon acidification to pH(o) 5.8, a significant decrease of the rapid adenosine triphosphate (ATP)-dependent inward m ovement of aminophospholipids was found at physiologic ionic concentra tion, whereas a change of pH from 7.4 to 8.5 did not affect this trans port, Evidence is given that the intracellular pH affects the active t ransport of aminophospholipids but not the extracellular pn. Suppressi on of the ATP-dependent outside-inside redistribution of aminophosphol ipid analogues by low pH was reversible because original transport act ivity was re-established upon reneutralization. pH dependence of the a ctive phospholipid transport was not caused by the spin-labeled report er group or by depletion of intracellular ATP, Because the same influe nce of pH on aminophospholipid movement could be observed for resealed ghosts, constituents of the red blood cell cytoplasm do not mediate t he influence of PH on the RTP-dependent inward movement of aminophosph olipids. (C) 1997 by The American Society of Hematology.