CYTOPLASMIC PH AND HUMAN ERYTHROCYTE SHAPE

Altered external pH transforms human erythrocytes from discocytes to s tomatocytes (low pH) or echinocytes (high pH). The mechanism of this t ransformation is unknown. The preceding companion study (Gedde and Hue stis) demonstrated that these shape changes are not mediated by change s in membrane potential, as has been reported. The aim of this study w as to identify the physiological properties that mediate this shape ch ange, Red cells were placed in a wide range of physiological states by manipulation of buffer pH, chloride concentration, and osmolality, Mo rphology and four potential predictor properties (cell pH, membrane po tential, cell water, and cell chloride concentration) were assayed. An alysis of the data set by stratification and nonlinear multivariate mo deling showed that change in neither cell water nor cell chloride alte red the morphology of normal pH cells. In contrast, change in cell pH caused shape change in normal-range membrane potential and cell water cells. The results show that change in cytoplasmic pH is both necessar y and sufficient for the shape changes of human erythrocytes equilibra ted in altered pH environments.