Local measurement of lateral motion in erythrocyte membranes by photobleaching technique

The lateral diffusion coefficients ($\text{D}$) of the molecular fluorescence probe 3,3′-dioctadecylindocarbocyanine iodide (DII) in the membrane of discoid erythrocyte ghosts has been measured with the photobleaching technique between 7°C and 40°C. A fluorescence microscope which allows bleaching experiments within small local fields (approx. 1 μm²) at high magnification (X1600) has been used for these measurements. The diffusion coefficient increases from $\text{D = 9 · 10}{}^{\mathrm{?10}}\text{cm}{}^2\text{/s}$ to $\text{D = 7.5 · 10}{}^{\mathrm{?9}}\text{cm}{}^2\text{/s}$ from 7 to 40°C. An increase in membrane fluidity between 12°C and 17°C indicates a conformational change of the lipid bilayer moiety in this temperature region. The diffusion coefficient measured in the regions between the spicules of echinocytes is appreciably smaller than in the untransformed discoid ghosts. In the myelin tubes originating from cells, the lateral diffusion is somewhat larger (about a factor of 2) than in the non-transformed ghosts. With the fluorescence probe technique the rate of growth of myelin tubes of 0.3 μm diameter has been estimated.