Studies of factors regulating the ageing of human erythrocytes. II. Metabolic depletion of erythrocytes is not accompanied by a decrease of their sialic acid content during blood bank storage.

Erythrocytes from human blood stored at 5 degrees C in anticoagulant-preservative solutions are considered, after a period from 21 to 24 days, unsuitable for transfusion. The nonviability of the cells appears due to metabolic impairment accompanied by a change of the biophysical properties of the cell but surprisingly not to a decrease of sialic acid of the membrane. The absence of proteolysis can be attributed to calcium chelation and to the stable levels of plasma protease inhibitors throughout the storage period. In fact, when erythrocytes are incubated for several days at 5 degrees C in protein-free media, release of sialopeptides from the membrane increases slowly and steadily, particularly if the medium is without glucose and adenine but contains divalent cations. Moreover, this phenomenon is strikingly amplified when incubation in protein-free media is carried out at 37 degrees C and once the ATP level has fallen below 5% of its initial value.