Transmembrane movement of diether phospholipids in human erythrocytes and human fibroblasts

We have synthesized spin-labeled (SL) and fluorescently labeled diacyl, 1-a lkyl-2-acyl-, and di-alkyl glycerophospholipids. The sn-2 chain was a short chain with either a nitroxide group or a 7-nitro-2,1,3-benzoxadiazol-4-yl (NBD), After incorporation in the exoplasmic leaflet of human erythrocytes, we found that SL-phosphatidylcholine (PC) redistributed very slowly across the plasma membrane, less than 20% reaching the cytoplasmic leaflet in 3 h at 37 degrees C. In contrast, SL-phosphatidylserine (PS) accumulated on th e cytoplasmic leaflet with the same plateau corresponding to 90% of the pro bes inside. The characteristic times for inward redistribution were differe nt for the three PS analogues: at 37 degrees C, the t(1/2) for the diacyl, alkyl-acyl, and dialkyl compounds were 2.3, 3.5, and 41 min, respectively. ATP depletion or incubation with N-ethylmaleimide inhibited the rapid trans location of the PS derivatives. The diether PS bearing an NBD group translo cated very slowly in human erythrocytes and no acceleration by ATP could be measured. On the other hand, in human fibroblasts, the diether NBD-PS and SL-PS were both transported from the exoplasmic to the cytoplasmic monolaye r of the plasma membrane as it is the case for the transport of the respect ive diester PS analogues. These results prove that the ether bends do not p revent completely PS binding and translocation by the aminophospholipid tra nslocase despite a probable hindrance due to the ether linkage on the sn-2 chain. Because of the high stability of the ether linkage, SL and NBD dieth er analogues should be useful to investigate lipid traffic in cultured cell s.