TRANSBILAYER MOBILITY AND DISTRIBUTION OF RED-CELL PHOSPHOLIPIDS DURING STORAGE

We studied phospholipid topology and transbilayer mobility in red cell s during blood storage. The distribution of phospholipids was determin ed by measuring the reactivity of phosphatidylethanolamine with fluore scamine and the degradation of phospholipids by phospholipase A2 and s phingomyelinase C. Phospholipid mobility was measured by determining t ransbilayer movements of spin-labeled phospholipids. We were unable to detect a change in the distribution of endogenous membrane phospholip ids in stored red cells even after 2-mo storage. The rate of inward mo vement of spin-labeled phosphatidylethanolamine and phosphatidylserine was progressively reduced, whereas that for phosphatidylcholine was i ncreased. These changes in phospholipid translocation correlated with a fall in cellular ATP. However, following restoration of ATP, neither the rate of aminophospholipid translocation nor the transbilayer move ment of phosphatidylcholine were completely corrected. Taken together, our findings demonstrate that red cell storage alters the kinetics of transbilayer mobility of phosphatidylserine, phosphatidylethanolamine , and phosphatidylcholine, the activity of the aminophospholipid trans locase, but not the asymmetric distribution of endogenous membrane pho spholipids, at least at a level detectable with phospholipases. Thus, if phosphatidylserine appearance on the outer monolayer is a signal fo r red cell elimination, the amount that triggers macrophage recognitio n is below the level of detection upon using the phospholipase techniq ue.