Rearrangement of intramembranous particles and fusion promoted in chicken erythrocytes by intracellular Ca 2+

Abstract

Ca 2+ was introduced into fresh and ATP-depleted chicken erythrocytes through the aid of the ionophore A-23187. Intracellular Ca 2+ (10–40 mM) induced fusion in ATP-depleted cells after 30–60 min incubation at 37°C, but not in fresh cells. Fresh cells underwent a higher degree of haemolysis than ATP-depleted cells after accumulation of Ca 2+. Uptake of Ca 2+ was the same in these two systems. Intracellular Ca 2+ induced rearrangement of intramembranous particles, as revealed by freeze-etching studies. The intramembranous particles in the protoplasmic face of fractured membranes obtained from fresh cells incubated with 1 mM of Ca 2+ were more scattered and their density was lower than in control cells. Incubation with higher concentrations of Ca 2+ (10–40 mM) induced transient changes in the intramembranous particles' density with the appearance of protrusions and depressions on the protoplasmic and exoplasmic faces of the fractured membranes, respectively. These effects were reversible upon removal of Ca 2+ by washing the cells with ethyleneglycol bis(α- aminoethylether)-N,N′- tetraacetic acid; rearrangement of intramembranous particles was less evident after accumulation of Ca 2+ in ATP-depleted cells, whose fractured membranes did not contain any protrusions or depressions. Transferring Ca 2+-loaded cells to the cold caused the formation of large smooth areas devoid of intramembranous particles in the protoplasmic face of the fractured membranes. Cells containing Ca 2+ appeared spherical, and removal of Ca 2+ restored the normal oval shape of chicken erythrocytes.