The Discocyte-Echinocyte Transformation: Comparison of Normal and ATP-enriched Human Erythrocytes

This work studies the relationship existing between intracellular ATP levels and the discocyte-echinocyte shape equilibrium in normal as well as ATP-enriched human red blood cells. Fresh erythrocytes metabolically depleted by incubation in a glucosefree buffer undergo echinocytic transformation (crenation) as intracellular ATP levels decline below 50% of their original value. When ATP is regenerated by further incubation of the same cells in the presence of glucose, inosine, and adenine (GIA), concentrations required for the complete recovery of the discocytic shape are lower than those which were necessary to maintain this shape in the first place. Addition of inorganic phosphate (Pi) to the GIA medium results in elevation of fresh cell ATP to supranormal levels. When such ATP-enriched cells are then depleted in the presence of the same concentration of inorganic phosphate, echinocytic transformation occurs much more rapidly than in normal fresh cells not previously incubated with Pi despite a similar rate of ATP depletion in both cases. It is suggested that the intrinsic mechanism responsible for shifting the discocyte-echinocyte equilibrium in the human erythrocyte is dependent on one or more intracellular or intramembrane factors occurring in conjunction with ATP depletion or repletion rather than to the absolute concentration of this nucleotide within the cell. This additional factor(s) appears to be temperature dependent and is influenced by the concentration of Pi in the medium.