Low pH induced shape changes and vesiculation of human erythrocytes

Shape changes and vesiculation were induced in intact human erythrocytes by gradually decreasing pH in the cell suspension. A sequence of different shapes preceding vesiculation was documented, i.e. discocytes, stomatocytes, and stomatoacantocytes. The final state was characterized by spherical mother cells and vesicles released. Low pH-induced vesiculation was also studied in the presence of stomatocytogenic or echinocytogenic compounds. The action of stomatocytogenic compounds was inhibitory, and echinocytogenic compounds had no effect on low pH-induced vesiculation. Vesiculation induced by low pH was studied also in isotonic solutions of different sucrose/salt composition. It was concluded that (i) low intracellular pH is responsible for cell shape transformations as well as for release of vesicles, (ii) at temperature 37 degrees C the intracellular pH value which induces the release of vesicles is 5.4, and (iii) the sequence of typical shape changes preceding vesiculation does not include echinocytes. The results are discussed on the basis of the layered membrane model of the shape formation and shape transformations of the human erythrocyte, and additionally considering the partial detachment of the membrane skeleton from the bilayer part of the membrane.