SHAPE RESPONSE OF HUMAN ERYTHROCYTES TO ALTERED CELL PH

Alteration of red blood cell (RBC) pH produces stomatocytosis (at low pH) and echinocytosis (at high pH). Cell shrinkage potentiates high pH echinocytosis, but shrinkage alone does not cause echinocytosis. Mech anisms for these shape changes have not been described. In this study, measured dependence of RBC shape on cell pH was nonlinear, with a bro ad pH range in which normal discoid shape was maintained. Transbilayer distribution of phosphatidylcholine and phosphatidylserine, measured by back-extraction of radiolabeled lipid, was the same in control and altered pH cells. Possible roles of pH-titratable inner monolayer phos pholipids were examined by assessing pH-dependent shape in cells in wh ich their levels had been perturbed. In metabolically depleted cells a nd calcium-treated cells, which have altered levels of phosphatidic ac id, phosphatidylinositol-4-phosphate, and/or phosphatidylinositol-4,5- bisphosphate, low cell pH was stomatocytogenic and high cell pH was ec hinocytogenic, as in control cells. Thus, neither change in membrane l ipid asymmetry nor normal levels of the pH-titratable inner monolayer lipids is necessary for cell pH-mediated shape change. (C) 1995 by The American Society of Hematology.