Redistribution of SL-PE in human erythrocytes suspended in media of high (120 mmol/L NaCl) or low ionic concentration (5 mmol/L NaCl) at neutral and acidic pH (4°C). After incorporation of SL-PE, the redistribution kinetics were monitored by the back-exchange of analogues on the outer leaflet to BSA (see the Materials and Methods). High ionic concentration: pH 5.8 (○); low ionic concentration: pH 5.8 (▿), pH 7.4 (▾). Curves were fitted by nonlinear regression to a monoexponential function.