Direct observation of membrane movement by electron microscopy.
Motions of wet lipid bilayer membranes and plasma membranes of human erythrocytes were observed directly in an electron microscope, using the techniques of selective area diffraction, diffraction contrast imaging and electron opaque markers. The motions are measured as functions of temperature. At the liquidus state of the membrane, the lateral diffusion coefficient is deduced from the Brownian motion of the labeling particles. The coefficient is measured to be 1.1 x 10(-10) cm2/sec. for a bilayer of an equimolar mixture of cholesterol and dipalmitoylphosphatidylcholine at 20 degrees C. The value for human erythrocyte membrane at 37 degrees C is similar. At the temperature where phase separation occurs, motion is detected as the solidus domains floating on a liquidus medium. Below the transition temperature, the solidus domains move relative to one another along the domain boundaries, the drift velocity being 3 x 10(-6) cm/sec. for the above mentioned bilayer, at 4 degrees C. Together with specific labeling technique, the electron optical method may be used to study the movement of specific sites relative to the membrane, on a scale beyond the resolving power of light microscopy. The use of scanning electron microscopy is discussed.
D004058:Diffusion; D004910:Erythrocyte Membrane / Q000378:metabolism / Q000648:ultrastructure*; D004912:Erythrocytes / Q000648:ultrastructure*; D006801:Humans; D008567:Membranes, Artificial; D008854:Microscopy, Electron / Q000295:instrumentation / Q000379:methods; D008954:Models, Biological; D010713:Phosphatidylcholines
D008567:Membranes, Artificial; D010713:Phosphatidylcholines