Effective bilayer expansion and erythrocyte shape change induced by monopalmitoyl phosphatidylcholine. Quantitative light microscopy and nuclear magnetic resonance spectroscopy measurements

When human erythrocytes are treated with exogenous monopalmitoyl phosphatidylcholine (MPPC), the normal biconcave disk shape red blood cells (RBC) become spiculate echinocytes. The present study examines the quantitative aspect of the relationship between effective bilayer expansion and erythrocyte shape change by a newly developed method. This method is based on the combination of direct surface area measurement of micropipette and relative bilayer expansion measurement of 13C crosspolarization/magic angle spinning nuclear magnetic resonance (NMR). Assuming that 13C NMR chemical shift of fatty acyl chain can be used as an indicator of lateral packing of membrane bilayers, it is possible for us to estimate the surface area expansion of red cell membrane induced by MPPC from that induced by ethanol. Partitions of lipid molecules into cell membrane were determined by studies of shape change potency as a function of MPPC and red cell concentration. It is found that 8(+/- 0.5) x 10(6) molecules of MPPC per cell will effectively induce stage three echinocytes and yield 3.2(+/- 0.2)% expansion of outer monolayer surface area. Surface area of normal cells determined by direct measurements from fixed geometry of red cells aspirated by micropipette was 118.7 +/- 8.5 microns2. The effective cross-sectional area of MPPC molecules in the cell membrane therefore was determined to be 48(+/- 4) A2, which is in agreement with those determined by x-ray from model membranes and crystals of lysophospholipids. We concluded that surface area expansion of RBC can be explained by a simple consideration of cross-sectional area of added molecules and that erythrocyte shape changes correspond quantitatively to the incorporated lipid molecules