TRANSMEMBRANE MOBILITY AND DISTRIBUTION OF PHOSPHOLIPIDS IN THE MEMBRANE OF MOUSE BETA-THALASSEMIC RED-BLOOD-CELLS

Using spin-labelled lipid analogues, the transmembrane mobility and di stribution of phospholipids in normal and beta-thalassaemic murine red blood cells were investigated. The velocities of spin-labelled phosph atidylserine (PS) and spin-labelled phosphatidylethanolamine (PE*) ac tive transport into the inner leaflet were not significantly different between normal and pathological cells. The stationary distribution of PE in thalassaemic erythrocytes (79.5 +/- 2.0% inside) differed from that of control cells (91.1 +/- 1.6% inside), while that of PS was u naffected. In thalassaemic cells the passive diffusion of spin-labelle d phosphatidylcholine (PC) was accelerated 4-fold and its stationary distribution was shifted to 34.5 +/- 2.3% inside compared to 19.5 +/1.6% in control cells. Spin-labelled sphingomyelin (SM), which showed no inward movement in normal cells, diffused partially towards the in ner leaflet of thalassaemic erythrocyte membranes. These results indic ate that modifications of the transverse lipid organisation in beta-th alassaemic red blood cells are due to changes in passive diffusion mov ements, and not to changes in aminophospholipid translocase activity.